Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review

Li Zhang; Geng Liu; Bing Han; Zhe Wang; Yuzhou Yan; Jianbing Ma; Pingping Wei

doi:10.1155/2020/7451683

Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review

Zhang, Li;Liu, Geng;Han, Bing;Wang, Zhe;Yan, Yuzhou;Ma, Jianbing;Wei, Pingping 2020-04-04 00:00:00 Hindawi Applied Bionics and Biomechanics Volume 2020, Article ID 7451683, 22 pages https://doi.org/10.1155/2020/7451683 Review Article Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review 1 1 1 1 1 2 Li Zhang , Geng Liu , Bing Han , Zhe Wang , Yuzhou Yan , Jianbing Ma , and Pingping Wei Shaanxi Engineering Laboratory for Transmissions and Controls, Northwestern Polytechnical University, Xi'an 710072, China Hong-Hui hospital, Xi’an Jiaotong University College of Medicine, Xi'an 710054, China State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi'an 710054, China Correspondence should be addressed to Geng Liu; npuliug@nwpu.edu.cn Received 8 November 2019; Accepted 1 February 2020; Published 4 April 2020 Academic Editor: Stefano Zaﬀagnini Copyright © 2020 Li Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The knee joint, as the main lower limb motor joint, is the most vulnerable and susceptible joint. The knee injuries considerably impact the normal living ability and mental health of patients. Understanding the biomechanics of a normal and diseased knee joint is in urgent need for designing knee assistive devices and optimizing a rehabilitation exercise program. In this paper, we systematically searched electronic databases (from 2000 to November 2019) including ScienceDirect, Web of Science, PubMed, Google Scholar, and IEEE/IET Electronic Library for potentially relevant articles. After duplicates were removed and inclusion criteria applied to the titles, abstracts, and full text, 138 articles remained for review. The selected articles were divided into two groups to be analyzed. Firstly, the real movement of a normal knee joint and the normal knee biomechanics of four kinds of daily motions in the sagittal and coronal planes, which include normal walking, running, stair climbing, and sit-to-stand, were discussed and analyzed. Secondly, an overview of the current knowledge on the movement biomechanical eﬀects of common knee musculoskeletal disorders and knee neurological disorders were provided. Finally, a discussion of the existing problems in the current studies and some recommendation for future research were presented. In general, this review reveals that there is no clear assessment about the biomechanics of normal and diseased knee joints at the current state of the art. The biomechanics properties could be signiﬁcantly aﬀected by knee musculoskeletal or neurological disorders. Deeper understanding of the biomechanics of the normal and diseased knee joint will still be an urgent need in the future. 1. Introduction knee to withstand tremendous forces during various normal movements [1]. Therefore, it is an urgent need to study the Since the number of the old and obese worldwide has been movement biomechanics of the normal and diseased knee increasing yearly, the research on human motion dysfunc- joint for the assistance or rehabilitation of human locomo- tion is getting more and more attention. The knee joint, as tor function. the main lower limb motor joint, is the most vulnerable In the last decade, several related review papers appeared and susceptible joint [1]. Knee impairments are the com- and could be divided into two aspects, normal knee biome- mon physical problems which impact the normal living chanics and diseased knee biomechanics. For the former, ability and mental health of these patients [2]. The inﬂu- Masouros et al. [5] analyzed the knee kinematics and ences mainly contain the supporting body weight, the assist- mechanic and surrounding soft tissue in detail. The research ing lower limb swing, and the absorbing strike shock [3]. pointed out that the knowledge of these structures was very useful for the diagnosis and evaluations of treatment. Wang The movement biomechanics, as an important branch of biomechanics, studies the coordination of the bones, mus- et al. [6] reviewed the modeling and simulation methods of cles, ligament, and tendons in various human movements human musculoskeletal systems. The knee kinematics and [4]. The complex interaction of these structures allows the kinetics in six common motions including walking, jogging, 2 Applied Bionics and Biomechanics stair ascent, stair descent, squatting, and kneeling were dis- 2. Methods cussed. Chhabra et al. [1] reported the anatomic structures This review was conducted in accordance with Preferred and their relationships in the uninjured knee joint, which Reporting Items for Systematic Reviews and Meta-Analyses provided the critical guidance for the reconstruction of the (PRISMA) [11]. We systematically searched electronic data- multiple ligament injured knee joint. Madeti et al. [4] dis- bases including ScienceDirect, Web of Science, PubMed, cussed various model formulations of the knee joint, includ- Google Scholar, and IEEE/IET Electronic Library for poten- ing mathematical, two-dimensional, and three-dimensional tially relevant articles. The following terms were used as key- models. And the forces acting on the knee joint had also words (identical for all databases): “knee joint,”“gait,”“knee been compared. For the latter, Flandry et al. [7] provided biomechanics,”“knee disease,” and “sports biomechanics.” an overview of the surgical anatomy of the knee joint and Given the fast advancement in acquisition equipment and emphasized connective tissue structures and common injury theoretical research of knee biomechanics, the search time patterns. Woo et al. [8] reviewed the biological and biome- range was set from 2000 to November 2019. A total of 1787 chanical knowledge of normal knee ligaments, as well as articles were retrieved initially. The daily life activities were the anatomical, biological, and functional perspectives of mainly considered in this review, the articles about more the current reconstruction knowledge following knee liga- complex activities, such as squats, hops, cut manoeuvres, ment injuries. The research also provided guidance for were excluded. After 679 articles were excluded, 1108 articles improving the treatment of knee ligament injuries. Louw about daily life activities were selected. In addition, review of et al. [9] assessed the eﬀects of the occluded vision on the all references cited by the selected articles and more insight knee kinematics and kinetics during functional activities, into other relevant authors’ studies yielded an additional 35 such as squatting, stepping down, drop landing, hopping, articles for possible inclusion. Then, all selected articles were and cutting movements in healthy individuals and the input into Excel to eliminate duplicates. After 511 duplicates individuals with anterior cruciate ligament injury or recon- were removed, 632 articles were assessed for inclusion. struction. Sosdian et al. [10] discussed the eﬀects of knee Studies were considered eligible if they met the following arthroplasty on the kinematics and kinetic properties of inclusion criteria: normal knee kinematics related, normal the frontal plane and sagittal plane during the stance knee dynamics related, diseased knee kinematics related, dis- phase of normal walking. The results showed that the peak eased knee dynamics related, English, and full-text articles. knee adduction angle and moment were decreased, but the Two reviewers (LZ and ZW) independently assessed the title peak knee ﬂexion moment was increased after knee and abstracts of the potential studies. After an initial deci- arthroplasty. However, to our knowledge, there is no sion, the full text of the studies that potentially met the review that synthesized the literature discussing the move- inclusion criteria were assessed before a ﬁnal decision was ment biomechanics of both the normal and the diseased made. A senior reviewer (GL) was consulted in cases involv- knee joint. ing disagreement. After exclusion of irrelevant titles and Understanding the knee biomechanics is a prerequisite screening of abstracts, 203 articles remained. Subsequently, for designing knee assistive devices and optimizing rehabil- detailed full-text screening based on the inclusion criteria itation exercises. This paper provides an overview of the was carried out, and 65 articles were excluded. Finally, 138 current biomechanical knowledge on normal and injured full-text articles were examined for full review. The search knee joints. For better assessment of the function of the process is demonstrated using the following diagram shown knee joint, the biomechanical parameters including angle, in Figure 1. moment, power, and stiﬀness from various researchers in diﬀerent daily motions are reviewed and compared. For 3. Results better understanding the kinematics and kinetics of real knee movement, the polycentric rotation in the sagittal We divided the 138 selected articles, which fulﬁlled the liter- plane and biomechanics in the coronal plane are also dis- ature search inclusion criteria, into two groups: biomechani- cussed. Further, the common knee disorders including cal properties of normal knee joint and biomechanical musculoskeletal and neurological disorders and their properties of diseased knee joint. For the former, the real inﬂuences on the knee biomechanics are also reviewed movement of a normal knee joint and the normal knee bio- and discussed. We hypothesized that the comprehensive mechanics of four kinds of daily motions in the sagittal and understanding of the knee joint biomechanics in physiolog- coronal planes, which include normal walking, running, ical and pathological conditions could signiﬁcantly improve stair climbing, and sit-to-stand, were discussed and ana- the design of knee assistive devices and rehabilitation lyzed. For the latter, an overview of the current knowledge exercise programs. on the movement biomechanical eﬀects of common knee The rest of this paper is organized as follows. In Section 2, musculoskeletal disorders (KOA) and knee neurological the search strategies adopted for the literature review are disorders (SCI, stroke, and CP) were provided. provided. In Section 3, the selected literatures including the biomechanical properties of normal knee joint and 3.1. Biomechanical Properties of Normal Knee Joint the knee diseased eﬀects on the biomechanics are summa- rized. In Section 4, the limitations of the current studies 3.1.1. Knee Biomechanics of Daily Motions in Sagittal Plane. are brieﬂy discussed and the recommendations for future Walking, running, stair climbing, and sit-to-stand are very research are provided. frequent motions in human’s daily life. In all of the motions, Applied Bionics and Biomechanics 3 Records indentiﬁed through Additional records identiﬁed database searching through other sources (n = 1787) (n = 38) Complex activities excluded (n = 679) Selected articles (n = 1108) Duplicates removed (n = 1143) Records excluded (n = 511) Title and abstract review (n = 632) Title and abstract excluded, with reasons (n = 429) Full-text articles for eligibility (n = 203) Full-text articles excluded, with reasons (n = 65) Studies included in systematic review (n = 138) Figure 1: The PRISMA ﬂow diagram of study selection process. the main functions of the knee joint include supporting points A, B, C, and D are from 6 to 28 deg, -2 to 5 deg, 53 to 78 deg, and -5 to 16 deg, respectively. In general, the the body weight (BW), absorbing shock of heel strikes, and assisting lower limbs swing [3]. According to the pre- ROM is around 53 to 75 deg for normal walking. vious researches, the passive knee ﬂexion could reach Figure 2(c) shows the typical knee moment-time curve. There 160 deg in the sagittal plane [1, 5, 12]. The peak load are two peak extension (E and G) and ﬂexion (F and H) through the knee joint is 2-3 BW during walking, 2-5 moments. Point H occurs in the swing phase and the others BW during sit-stand-sit, 4-6 BW during stair climbing, occur in the stance phase. Table 2 gives the values of these and 7-12 BW during running [12–14]. In this section, the points from 11 studies. The values of these points vary consid- ROM, maximum moment, maximum power, and stiﬀness erably between diﬀerent studies. The ranges of points E, F, G, of the knee joint are mainly discussed because they are the and H are from 0.129 to 0.945 Nm/kg, -0.675 to 0.067 Nm/kg, key indexes for the design of knee assistive device and opti- 0.101 to 0.466 Nm/kg, and -0.420 to 0.086 Nm/kg, respec- mization of rehabilitation exercises. tively. The ﬁrst peak extension moment is always greater than As shown in Figure 2(a), the walking gait can be divided the second. But it is hard to determine who is bigger between into two main phases: stance (about 0-65% of gait) and swing the two peak ﬂexion moments. In general, the range of moment is about 0.458 to 1.265 Nm/kg for normal walking. phases (about 65-100% of gait) [15, 16]. The stance phase consists of three subphases: initial (heel strike to foot ﬂat), Figure 2(d) shows the typical knee power-time curve. It middle (foot ﬂat to opposite heel strike), and terminal stance includes one peak generation power (J) and three peak (opposite heel strike to toe oﬀ) [16, 17]. The knee joint in the absorption powers (I, K, and L). Point L occurs in the swing stance phase is regarded as a shock damping mechanism to phase and the others occur in the stance phase. For the knee joint, there is only absorption power in the swing phase. accept the BW [18]. The swing phase consists of two sub- phases: initial (toe oﬀ to knee maximum ﬂexion) and termi- And in the whole gait cycle, knee absorption powers are much nal swing (knee maximum ﬂexion to heel strike) [16, 17]. larger than generation powers. Mooney and Herr [22] found The main function of the knee in the swing phase is assisting that the mean net knee power is about -18 W (mean genera- ﬂexion-extension for toe clearance, foot placement, and tak- tion and absorption power is about 18 W and -36 W, respec- tively). Table 3 gives the values of these points from 10 ing over the load in the next step [19, 20]. Zheng [21] reported that the knee biomechanics is aﬀected mainly by studies. The ranges of points I, J, K, and L are from -1.736 walking speed. With the speed increased, the ROM, maxi- to -0.116 W/kg, 0.286 to 0.834 W/kg, -1.935 to -0.403 W/kg, mum extension moment, and maximum absorption power and -2.712 to -0.321 W/kg, respectively. In general, the range would increase. Figure 2(b) shows the typical knee angle- of power is about 1.035 to 3.214 W/kg for normal walking. As shown in Figure 3(a), the running cycle can be divided time curve. There are two peak ﬂexion (A and C) and exten- sion (B and D) angles. Points A and B occur in the stance into four main phases: stance (heel strike to toe oﬀ), ﬁrst ﬂoat phase, and C and D occur in the swing phase. Comparing (toe oﬀ to opposite heel strike), swing (opposite heel strike to the two peak ﬂexion angles, the value in the swing phase is opposite toe oﬀ), and second ﬂoat phases (opposite toe oﬀ to always greater than that in the stance phase. Table 1 gives heel strike) [14]. The knee main function in running is simi- lar to that in walking. Comparing Figures 2 and 3, it can be the values of these points from 18 studies. The ranges of Included Eligibility Screening Identiﬁcation 4 Applied Bionics and Biomechanics Stance (65%) Swing (35%) Initial Middle Terminal Initial Terminal B D 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) –150 –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 2: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a walking gait cycle. (a) Sketch map of walking motion [14]. (b) Knee angle-time curve ((A) ﬁrst peak knee ﬂexion angle, (B) ﬁrst peak knee extension angle, (C) second peak knee ﬂexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee absorption power, (J) ﬁrst peak knee generation power, (K) second peak knee absorption power, and (L) third peak knee absorption power) [16, 17]. Table 1: Overview over the experimental results of knee angle for normal walking. Subjects (mean height ± SD (m), ° ° ° ° ° ° Study Speed (m/s) A ()B()C()D( ) C-A ( ) ROM ( ) mean weight ± SD (kg)) Collins et al. [125] 9 (1:84 ± 0:10, 77:4±9:2) 1.25 12 3 61 -5 49 66 Zheng [21] 1 (1.78, 70) 1.2 22 10 66 6 44 60 Wang [126], Lee et al. [17] 1 (1.69, 63.5) 1.5 7 3 53 -2 46 55 Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 28 5 78 4 50 74 Shamaei et al. [3, 127] 3 (1:76 ± 0:75, 68:6±2:2) 1.25 26 15 69 6 43 63 Blazkiewicz [128] 1 (1.85, 80) — 10 -2 53 0 43 55 Sridar et al. [34] 3 (1:70 ± 0:05, 74:7±8:4) 1.0 22 11 62 2 40 60 Knaepen et al. [129] 10 (1:82 ± 0:10, 77:5±11:7) 0.69 14 8 62 8 48 54 Shirota et al. [130] 4 (1:80 ± 0:08, 74 ± 6:8) 1.24 13 5 65 1 52 64 Gordon et al. [131] 3 (1:80 ± 0:01, 96 ± 9) 1.0 6 0 55 16 49 55 Ding et al. [132] 8 (1:76 ± 0:06, 78:5±9:9) 1.25 24 7 75 0 51 75 Winter [133], Li et al. [134] 1 (—, 58) 1.3 16 5 67 -2 51 69 Beyl et al. [135] —— 22 8 64 1 42 63 Baliunas et al. [136] 15 (1:68 ± 0:12, 74 ± 16) 0.98 17 3 60 -2 43 62 Yang et al. [137] 1 (1.75, 70) 1.0 14 3 56 6 42 53 A: ﬁrst peak knee ﬂexion angle; B: ﬁrst peak knee extension angle; C: second peak knee ﬂexion angle; D: second peak knee extension angle. Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 5 Table 2: Overview over the experimental results of knee moment for normal walking. Subjects (mean height ± SD (m), Speed E F G H E-G F-H Range Study mean weight ± SD(kg)) (m/s) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) Collins et al. [125] 9 (1:84 ± 0:10, 77:4±9:2) 1.25 0.556 -0.245 0.207 -0.388 0.349 0.143 0.944 Shamaei et al. [3] 3 (1:76 ± 0:75, 68:6±2:2) 1.25 0.335 -0.248 0.102 -0.379 0.233 0.131 0.714 Zheng [21] 1 (1.78, 70) 1.2 0.571 -0.171 0.114 0.086 0.457 -0.257 0.742 Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 0.766 -0.344 0.189 -0.378 0.577 0.034 1.144 Blazkiewicz [128] 1 (1.85, 80) — 0.263 -0.675 0.225 -0.063 0.038 -0.612 0.938 Ding et al. [132] 8 (1:76 ± 0:06, 78:5±9:9) 1.25 0.777 -0.204 0.204 -0.420 0.573 0.198 1.197 Winter [133], Li et al. [134] 1 (—, 58) 1.3 0.517 -0.155 0.189 -0.224 0.328 0.069 0.741 Yang et al. [137] 1 (1.75, 70) 1.0 0.129 -0.329 0.101 -0.257 0.028 -0.072 0.458 Dijk et al. [138] 8 (1:79 ± 0:04, 75:1±6:5) 1.11 0.945 0.067 0.466 -0.320 0.479 -0.387 1.265 Briggs et al. [51] 20 (1:67 ± 0:11, 58:0±12:6) — 0.534 -0.276 0.190 — 0.344 —— E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. Table 3: Overview over the experimental results of knee power for normal walking. Subjects (mean height ± SD (m), Study Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg) mean weight ± SD (kg)) Collins et al. [125] 9 (1:84 ± 0:10, 77:4± 9:2) 1.25 -0.571 0.286 -1.057 -1.457 1.743 Zheng [21] 1 (1.78, 70) 1.2 -0.489 0.591 -0.469 -0.321 1.080 Mooney et al. [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 -0.889 0.834 -1.334 -1.639 2.473 Malcolm et al. [16] 8 (1:67 ± 0:02, 60 ± 1) 1.38 -1.736 0.502 -0.763 -2.712 3.214 Ding et al. [132] 8 (1:76 ± 0:06, 78:5± 9:9) 1.25 -0.968 0.606 -1.290 -1.677 2.283 Winter [133], Li et al. [134] 1 (—, 58) 1.3 -0.755 0.324 -0.924 -1.247 1.571 Yang et al. [137] 1 (1.75, 70) 1.0 -0.116 0.296 -0.403 -0.739 1.035 Dijk et al. [138] 8 (1:79 ± 0:04, 75:1± 6:5) 1.1 -1.242 0.586 -1.509 -1.329 2.095 Walsh et al. [139] 1 (—, 60) 0.8 -0.828 0.667 -1.935 -1.410 2.602 I: ﬁrst peak knee absorption power; J: ﬁrst peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power. observed that the curves of angle, moment, and power in As shown in Figure 4(a), the stair climbing cycle (includ- ing stair ascent and descent) can be divided into two main running are also similar to that in walking. Hamner and Delp [23] reported that the knee biomechanics is mainly aﬀected phases: stance phase (about 0-62% of the cycle) and swing by running speed. With increasing speed, the ROM, maxi- phase (about 62-100% of the cycle) [24, 25]. The stance phase mum extension moment, and maximum absorption power consists of three subphases: initial (foot contact to opposite would increase. Figure 3(b) shows the typical knee angle- toe oﬀ), middle (opposite toe oﬀ to opposite foot contact), time curve in a gait cycle and Table 4 gives the angles of and terminal stance (opposite foot contact to toe oﬀ) points A, B, C, and D from 7 studies. The ranges of points [24, 26, 27]. Riener et al. [24] indicated that the knee bio- A, B, C, and D are from 36 to 60 deg, 13 to 29 deg, 80 to mechanics is mainly aﬀected by the rate of leg length and 129 deg, and 10 to 21 deg, respectively. In general, the ROM stair height. Figure 4(b) shows the typical knee angle-time of the knee joint is around 60 to 115 deg for running. curves in a stair ascent and stair descent cycle. They all Figure 3(c) shows the typical knee moment-time curve in a include one peak ﬂexion (A) and extension (B) angle. For running cycle and Table 5 gives the moments of points E, stair ascent, point A occurs in the swing phase and B occurs F, G, and H from 5 studies. The ranges of points E, F, G, in the terminal stance phase. And for stair descent, point A and H are from 1.157 to 2.574 Nm/kg, -0.259 to 0.320 Nm/kg, occurs in the terminal stance phase and B occurs in the swing 0.135 to 0.585 Nm/kg, and -1.474 to -0.277 Nm/kg, respec- phase. Table 7 gives the values of these points from 7 studies. tively. The range of moment is about 1.434 to 3.904 Nm/kg The ranges of points A and B are from 83 to 102 deg and 0 to for running. Figure 3(d) shows the typical knee power-time 11 deg for stair ascent and from 83 to 105 deg and 1 to 19 deg curve in a running cycle and Table 6 gives the powers of points for stair descent, respectively. In general, the ROM of the knee joint is around 78 to 94 deg for stair ascent and 76 to I, J, K, and L from 6 studies. The ranges of points I, J, K, and L are from -1.706 to -12.567 W/kg, 2.739 to 9.405 W/kg, -3.456 90 deg for stair descent. Figure 4(c) shows the typical knee to -1.525 W/kg, and -3.456 to -6.732 W/kg, respectively. The moment-time curves in a stair ascent and descent cycle. range of power is about 8.724 to 21.972 W/kg. This empha- They all include two peak extension (E and G) and ﬂexion sizes that the ranges of knee angle, moment, and power in (F and H) moments. For stair ascent, points E and F occur in the stance phase and G and H occur in the swing running are far more than those in normal walking. 6 Applied Bionics and Biomechanics B D Float Float Stance (40%) Swing (30%) (15%) (15%) 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) –150 I K –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 3: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a running cycle. (a) Sketch map of running motion [14]. (b) Knee angle-time curve ((A) ﬁrst peak knee ﬂexion angle, (B) ﬁrst peak knee extension angle, (C) second peak knee ﬂexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee absorption power, (J) ﬁrst peak knee generation power, (K) second peak knee absorption power, and (L) third peak knee absorption power) [23, 122, 123]. Table 4: Overview over the experimental results of knee angle for running. Subjects (mean height ± SD (m), ° ° ° ° ° ° Study Speed (m/s) A ()B()C()D( ) C-A ( ) ROM ( ) mean weight ± SD (kg)) 2.1 36 22 80 20 44 60 Zheng [21] 1 (1.78, 70) 2.8 49 20 90 17 41 73 2.0 42 18 85 11 43 74 3.0 44 16 103 12 59 91 Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9±7:0) 4.0 46 15 119 13 73 106 5.0 47 15 129 14 82 115 Dollar et and Herr[122] 1 (—, 85) 3.2 43 23 89 21 46 68 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 44 15 105 13 61 92 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8± 11) 2.48 48 17 86 10 38 76 Miller et al. [141] 12 (1:66 ± 0:05, 61 ± 4:7) 3.8 60 29 96 16 36 80 Ferber et al. [52] 20 (1:81 ± 0:06, 82:3±11:8) 3.65 46 13 —— — — A: ﬁrst peak knee ﬂexion angle; B: ﬁrst peak knee extension angle; C: second peak knee ﬂexion angle; D: second peak knee extension angle. phase. And for stair descent, points E, F, and G occur in the to -0.145 Nm/kg, 0.027 to 0.144 Nm/kg, and -0.314 to stance phase and H occurs in the swing phase. Table 8 gives -0.121 Nm/kg for stair ascent and from 0.007 to 1.512 Nm/kg, the values of these points from 7 studies. The ranges of points -0.070 to 0.662 Nm/kg, 0.365 to 1.620 Nm/kg, and -0.266 E, F, G, and H are from 0.454 to 1.409 Nm/kg, -0.556 to 0.040 Nm/kg for stair descent, respectively. In general, Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 7 Table 5: Overview over the experimental results of knee moment for running. Subjects (mean height ± SD (m), Speed E F G H E-G F-H Range Study mean weight ± SD (kg)) (m/s) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) 2.1 1.157 -0.030 0.274 -0.277 0.883 0.247 1.434 Zheng [21] 1 (1.78, 70) 2.8 1.749 0.320 0.320 -0.351 1.429 0.671 2.100 2.0 1.798 -0.205 0.135 -0.697 1.663 0.492 2.495 3.0 2.159 -0.226 0.269 -0.925 1.890 0.699 3.084 Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9±7:0) 4.0 2.402 -0.233 0.405 -1.147 1.997 0.914 3.549 5.0 2.430 -0.259 0.585 -1.474 1.845 1.215 3.904 Dollar and Herr [122] 1 (—, 85) 3.2 1.571 0.175 0.175 -0.591 1.396 0.766 2.162 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 2.196 -0.249 0.248 -0.775 1.948 0.526 2.971 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8±11) 2.48 2.574 -0.221 0.307 -0.649 2.267 0.428 3.223 E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. Table 6: Overview over the experimental results of knee power for running. Subjects (mean height ± SD (m), Study Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg) mean weight ± SD (kg)) 2.1 -5.859 4.336 -2.231 -3.521 10.195 Zheng [21] 1 (1.78, 70) 2.8 -8.008 7.386 -3.456 -3.456 15.394 Dollar and Herr [122] 1 (—, 85) 3.2 -1.706 4.766 -1.525 -3.958 8.724 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 -9.013 4.539 -2.439 -6.732 13.552 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8±11) 2.48 -12.567 9.405 -2.371 -4.473 21.972 Ferber et al. [52] 20 (1:81 ± 0:06, 82:3±11:8) 3.65 -5.462 2.739 —— — Heiderscheit et al. [62] 45 (1:76 ± 0:10, 69:5±13:1) 2.9 -6.948 5.422 —— — I: ﬁrst peak knee absorption power; J: ﬁrst peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power. the range of moment is about 1.010 to 1.815 Nm/kg for stair 6 studies. The ranges of points A and B are from 82 to ascent and 0.435 to 1.815 Nm/kg for stair descent. Figure 4(d) 96 deg and -3 to 22 deg, respectively. In general, the ROM of the knee joint is around 60 to 87 deg for sit-to-stand cycle. shows the typical knee power-time curves in a stair ascent and descent cycle. They all include two peak generation Table 11 gives the experimental results of knee moment from (I and K) and absorption (J and L) powers. For stair ascent, 9 studies. The ranges of points E and F are from 0.619 to the whole curve lies in the generation area mostly. And for 2.187 Nm/kg and -0.198 to 0.609 Nm/kg, respectively. In gen- stair descent, the whole curve lies in the absorption area eral, the range of moment is about 0.619 to 1.578 Nm/kg for mostly. Table 9 gives the values of these points from 4 stud- sit-to-stand cycle. The researchers about knee power in sit- ies. The ranges of points I, J, K, and L are from -1.044 to to-stand is rare, and only two researchers have been found. 2.887 W/kg, -0.228 to 0.071 W/kg, 0.447 to 1.020 W/kg, and Spyropoulos et al. [29] reported that the knee power was -0.739 to -0.265 W/kg for stair ascent and from -0.212 to about 1.973 W/kg for sit-to-stand. But Kamali et al. [30] 0.569 Nm/kg, -3.621 to -0.248 Nm/kg, -1.326 to -0.429, and pointed out that the value was about 0.560 W/kg for -5.485 to -2.077 Nm/kg for stair descent, respectively. In sit-to-stand. general, the range of power is about 1.309 to 3.481 W/kg for Because of the complicated interaction of the underlying stair ascent and 2.114 to 6.054 W/kg for stair descent. biological mechanisms, the knee joint demonstrates a spring- As shown in Figure 5(a), the sit-to-stand begins in a sit like behavior in common motions [31–33]. Figure 6 shows posture and ends in a stand posture. Figures 5(b)–5(d) show the typical knee moment-angle curves in the sagittal plane. the typical knee angle-time, moment-time, and power-time A linear relationship can be seen during the sit-to-stand, curves in sit-to-stand cycle, respectively. For the knee joint, and the weight acceptance and swing phase of walking, run- there are only extension angle, extension moment, and ning, and stair climbing. Quasistiﬀness refers to the slope of the linear ﬁt to the knee moment-angle curve [33]. During generation power in the whole sit-to-stand movement. The maximum angle, moment, and power occur in nearly the walking, running, and stair climbing, a high stiﬀness in the same time that the buttocks leave the chair. Hurley et al. weight acceptance phase and a low stiﬀness in the swing [28] represented that the biomechanics of knee joint is phase can be observed. For walking, Zhu et al. [20] and Wang mainly aﬀected by the rate of leg length and chair height. [12] found that the knee quasistiﬀness was around 3.0 and 2.27 Nm/deg in the stand phase. Sridar et al. [34] indicated Table 10 gives the experimental results of knee angle from 8 Applied Bionics and Biomechanics 100 AA Descent Stance (62%) Swing (38%) Initial Middle Terminal Ascent 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) 120 G Descent Ascent –150 J Ascent Descent L –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 4: A sketch map of motion and the typical curves of knee angle, moment, and power in sagittal plane for stair ascent and stair descent. (a) Sketch map of the stair ascent and stair descent motion. (b) Knee angle-time curve ((A) peak knee ﬂexion angle and (B) peak knee extension angle. (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee generation power, (J) ﬁrst peak knee absorption power, (K) second peak knee generation power, and (L) second peak knee absorption power) [24, 25]. Table 7: Overview over the experimental results of knee angle for stair ascent and stair descent. Subjects (mean height ± SD (m), ° ° ° Study Riser × tread (cm × cm) Type A ()B( ) ROM ( ) mean weight ± SD (kg)) Ascent 91 9 82 13:8×31:0 Descent 89 13 76 Ascent 95 9 86 17:0×29:0 Riener et al. [24], Joudzadeh et al. [25] 10 (1:79 ± 0:05, 82:2±8:5) Descent 93 15 78 Ascent 102 10 92 22:5×25:0 Descent 102 13 89 Ascent 99 11 88 22:0×28:0 Mcfadyen and Winter [142] 3 (—, —) Descent 105 19 86 Ascent 89 7 82 18:0×28:0 Zhang et al. [143] 10 (1:74 ± 0:05, 72:7±8:6) Descent 96 10 86 Ascent 83 5 78 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) Descent 83 6 77 Ascent 94 0 94 18:0×28:5 Protopapadaki et al. [144] 33 (1:69 ± 0:08, 67:5±12:1) Descent 91 1 90 Ascent 95 11 84 17:0×28:0 Law [26] 19 (1:64 ± 0:08, 59:5±7:8) Descent 93 3 90 A: peak knee ﬂexion angle; B: peak knee extension angle. Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 9 Table 8: Overview over the experimental results of knee moment for stair ascent and stair descent. Subjects (mean height ± SD (m), Riser × tread E F G H E-G F-H Range Study Type mean weight ± SD (kg)) (cm × cm) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) Ascent 1.055 -0.179 0.027 -0.183 1.028 0.004 1.238 13:8×31:0 Descent 0.916 0.587 1.247 -0.096 -0.331 0.683 1.343 Ascent 1.093 -0.218 0.042 -0.177 1.051 -0.041 1.311 Riener et al. [24] and Joudzadeh 17:0×29:0 10 (1:79 ± 0:05, 82:2±8:5) et al. [25] Descent 1.006 0.662 1.345 -0.091 -0.339 0.753 1.436 Ascent 1.164 -0.247 0.037 -0.172 1.127 0.075 1.411 22:5×25:0 Descent 0.991 0.653 1.470 -0.088 -0.479 0.741 1.558 Ascent 1.409 -0.406 0.164 -0.314 1.245 -0.092 1.815 22:0×28:0 Mcfadyen and Winter[142] 3 (—, —) Descent 1.512 0.405 1.620 -0.266 -0.108 0.671 1.886 Ascent 0.588 -0.493 0.144 -0.256 0.444 -0.237 1.081 18:0×28:0 Zhang et al. [143] 10 (1:74 ± 0:05, 72:7±8:6) Descent 0.338 0.152 1.106 -0.201 -0.768 0.353 1.307 Ascent 0.921 -0.456 0.043 -0.206 0.878 -0.250 1.377 ± 14) 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 Descent 0.448 0.263 1.012 -0.167 -0.564 0.430 1.179 Ascent 0.454 -0.556 0.032 -0.121 0.422 -0.435 1.010 18:0×28:5 Protopapadaki et al. [144] 33 (1:69 ± 0:08, 67:5±12:1) Descent 0.007 -0.070 0.365 -0.040 -0.358 -0.030 0.435 Ascent 0.899 -0.145 0.046 -0.147 0.085 0.002 1.036 17:0×28:0 Law [26] 19 (1:64 ± 0:08, 59:5±7:8) Descent 0.603 0.439 1.006 -0.076 -0.403 0.515 1.082 E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. 10 Applied Bionics and Biomechanics Table 9: Overview over the experimental results of knee power for stair ascent and stair descent. Subjects (mean height ± SD (m), Riser × tread I J K L Range Study Type mean weight ± SD (kg)) (cm × cm) (W/kg) (W/kg) (W/kg) (W/kg) (W/kg0 Ascent 2.322 0.071 0.647 -0.309 2.631 13:8×31:0 Descent 0.256 -0.678 -0.429 -3.788 4.044 Ascent 2.538 0.055 0.696 -0.312 2.850 Riener et al. [24] and 17:0×29:0 10 (1:79 ± 0:05, 82:2±8:5) Joudzadeh et al. [25] Descent 0.305 -1.029 -0.453 -4.141 4.446 Ascent 2.887 0.049 0.811 -0.288 3.175 22:5×25:0 Descent -0.212 -1.255 -0.472 -4.843 4.631 Ascent 2.742 -0.228 1.020 -0.739 3.481 22:0×28:0 Mcfadyen and Winter [142] 3 (—, —) Descent 0.569 -3.621 -1.326 -5.485 6.054 Ascent 1.044 -0.223 0.447 -0.265 1.309 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) Descent 0.037 -0.248 -0.558 -2.077 2.114 I: ﬁrst peak knee generation power; J: ﬁrst peak knee absorption power; K: second peak knee generation power; L: second peak knee absorption power. 100 A 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% sit-to-stand completion) (a) (b) 150 I –150 –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% sit-to-stand completion) Time (% sit-to-stand completion) (c) (d) Figure 5: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for sit-to-stand. (a) Sketch map of sit-to-stand cycle [28]. (b) Knee angle-time curve ((A) peak knee ﬂexion angle and (B) peak knee extension angle). (c) Knee moment- time curve ((E) peak knee extension moment and (F) peak knee ﬂexion moment). (d) knee power-time curve ((I) peak knee generation power) [37, 124]. that the knee quasistiﬀness was around 1.07 Nm/deg in the and 0.04 Nm/deg in the swing phase of stair ascent and stair swing phase. For running, Elliott et al. [35, 36] found that descent, respectively. For sit-to-stand, Wu et al. [37] reported the knee quasistiﬀness was around 0.38 Nm/deg in the swing that the knee quasistiﬀness was around 1.1 Nm/deg. phase and 6.6 Nm/deg in the stand phase. For stair climbing, Riener et al. [24] reported that the knee quasistiﬀness was 3.1.2. The Real Motion and Coronal Plane Biomechanics of around 2.37 Nm/deg and 2.42 Nm/deg in the weight accep- Knee Joint. Since the nonuniform shape of the knee articular tance phase of stair ascent and stair descent and 0.19 Nm/deg surface and the complicated physical structure of the femur Knee moment (Nm) Extension Knee power (W) Knee angle (deg) Flexion Generation Applied Bionics and Biomechanics 11 Table 10: Overview over the experimental results of knee angle for sit-to-stand. Subjects (mean height ± SD (m), ° ° ° Study A()B( ) ROM ( ) mean weight ± SD (kg)) Wu et al. [37] 1 (—, 75) 96 9 87 Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13)90 12 78 Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6±5)86 -1 87 Karavas et al. [124] 1 (1.85, 82.5) 86 5 81 Yu et al. [145] 10 (1:65 ± 0:05,46:2±0:8)82 22 60 Bowser et al. [146] 12 (1:66 ± 0:08, 74:2±19:5)83 -3 86 A: peak knee ﬂexion angle; B: peak knee extension angle. Table 11: Overview over the experimental results of knee moment for running. Subjects (mean height ± SD (m), Study E (Nm/kg) F (Nm/kg) Range (Nm/kg) mean weight ± SD (kg)) Wu et al. [37] 1 (—, 75) 2.187 0.609 1.578 Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13) 0.619 0 0.619 Yoshioka et al. [147] 1 (—, 73.8) 1.087 -0.038 1.125 Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6± 5) 1.132 -0.157 1.289 Karavas et al. [124] 1 (1.85, 82.5) 1.293 0.168 1.125 Bowser et al. [146] 12 (1:66 ± 0:08, 74:2±19:5) 0.901 0 0.901 Kamali et al. [30] 1 (1.72, 70) 1.126 0.136 0.990 Schoﬁeld et al. [148] 10 (1:77 ± 0:09, 70:5±8:7) 0.679 0.038 0.641 Robert et al. [149] 7 (1:75 ± 0:06, 66 ± 8) 1.136 -0.198 1.334 E: peak knee extension moment; F: peak knee ﬂexion moment. and tibia, the knee motion cannot be modeled as simple as a the knee extension motion [44, 45]. Blankevoort et al. [46], perfect hinge [38–40]. The real knee joint moves with a poly- Churchill et al. [47], and Hollister et al. [48] found that the centric motion, whereby the center of rotation changes dur- ﬂexion-extension and internal-external rotation cause the ing the rotation [41]. The femur and tibia can be trajectory of the knee center seem to be a spiral curve. approximated as a bielliptical structure, so the tibia rolls on In the coronal plane, the knee adduction moment and the loads of knee medial and lateral compartments are key the femur resulting in anterior-posterior (A-P) translation during the ﬂexion-extension motion [40]. When the rotation parameters of biomechanics. For the former, Gaasbeek et al. angle is less than 20 deg, there would be a small A-P transla- [49], Russell [50], and Briggs et al. [51] found that the maxi- tion. Thus, the movement of a real knee joint can be approx- mum adduction moment is about 0.31, 0.36, and imated as pure rolling around the ﬁxed center. But when the 0.26 Nm/(kg⋅m) in walking, respectively. Ferber et al. [52], rotation angle is more than 20 deg, the A-P translation begins Sinclair [53], and Gehring et al. [54] reported that the maxi- to increase, the amplitude of which can exceed 19 mm. Thus, mum adduction moment is about 0.52, 0.53, and the knee motion can be approximated as a gradual transition 0.58 Nm/(kg⋅m) in running, respectively. Law [26] and Mus- selman [27] represented that the maximum adduction from pure rolling, the coupled motion of rolling, and sliding to pure sliding [38, 40, 42]. Smidt [43] reported that the tra- moment is about 0.44 and 0.34 Nm/kg in stair climbing, jectory of the center of knee seems to be a J-shaped curve in respectively. Trepczynski et al. [55] reported that the maxi- the sagittal plane. mum adduction moment is about 0.45 Nm/kg in sit-to- In addition to the motion in the sagittal plane, the knee stand. For the latter, Russell [50] found that the normal knee joint always had a little varus, in other words, the medial joint also has internal-external rotation in the horizontal plane [44]. During the last 10-15 deg before complete exten- compartment bears more load than the lateral compartment. sion, the medial femoral condyle is internally rotated and the Specogna et al. [56] reported that the weight-bearing line tibia is externally rotated. At the same time, the lateral menis- (WBL) was diﬀerent in each phase of the gait. Cao [57] cus is anteriorly translated and the medial meniscus is poste- reported that the medial compartment bears 60-80% of the load. Pagani et al. [58] found that about 70% joint force pass riorly translated. Because of the larger contact surface of the medial tibiofemoral joint, the length of the medial femoral through the medial compartment to the ground. condyle is longer than that of the lateral, and because of the limitations of cruciate-collateral ligaments and quadriceps 3.2. Biomechanical Properties of Diseased Knee Joint. Accord- femoris on knee motion, the knee joint is self-locking as an ing to the pathogeny, the knee disorders can be mainly divided into musculoskeletal and neurological disorders. eccentric wheel to maintain the stability of the joint during Heel strike 12 Applied Bionics and Biomechanics 120 120 Stance Stance 0 0 Swing Swing Heel strike –60 –60 0 20 40 60 80 100 0 20406080 100 Knee angle (deg) Knee angle (deg) Flexion Flexion (a) (b) 120 120 Descent 60 60 Ascent 0 0 Sit Stand –60 –60 0 20406080 100 0 20406080 100 Knee angle (deg) Knee angle (deg) Flexion Flexion (c) (d) Figure 6: The moment-angle (stiﬀness) curves of the knee joint for normal walking, running, stair climbing, and sit-to-stand. (a) Normal walking [20, 34]. (b) Running [35, 36]. (c) Stair ascent and stair descent [24]. (d) Sit-to-stand [37]. For the former, the pathogeny is inside the knee joint, but the changes, enlarging bone marrow lesions, compartment carti- neural control system of these patients is normal. Knee oste- lage loss, joint space narrowing, and tibial plateau compres- oarthritis (KOA), knee ligament injury, and meniscus injury sion. [63, 68]. From the biomechanical view, these causes will change the tibiofemoral alignment and inﬂuence the load are the most common forms of these disorders and will be mainly discussed in this section. Some evidences showed that distribution, and then result in the deterioration of KOA the partial assistance from an external mechanism can allevi- [69]. Due to the medial compartment bearing about 70% of ate the symptoms [59]. For the latter, the actuator of the knee the total force, KOA is more commonly observed in the is normal, but the knee control system or more advanced medial compartment (MKOA) than the lateral compartment control system is injured. Although it is not considered a with a ratio of up to 4 times [58, 59]. knee joint disease in the medical ﬁeld, the neurological disor- Medical radiological assessment, kinematics analysis, ders can inﬂuence the knee movement biomechanics. Spinal kinetics analysis, and knee muscle analysis are the common cord injury (SCI), stroke, and cerebral palsy (CP) are the biomechanical methods for KOA, as shown in Table 12. In most common forms of these disorders and will be mainly the medical radiological assessment aspect, the hip-knee- discussed in this section. Some researchers pointed out that ankle angle (HKAA) on the full-0limb radiograph is regarded the partial or entire assistance from an external mechanism as the gold standard of alignment measurement, as shown in and rehabilitation training can recover the ambulatory ability Figure 7(a) [63, 69]. Chao et al. [70] reported that the normal of this patients [60, 61]. HKAA was about 178.8 deg and the angle is less than the value represented by genu varum. Russell [50] found that the 3.2.1. Knee Musculoskeletal Disorders and Its Biomechanical HKAA of normal and MKOA were about 177.7 deg and Eﬀects. KOA, one of the major health problems, aﬀects 174.2 deg, respectively. As shown in Figure 7(a), mechani- 7-17% of individuals especially for the elder, obese, and cal-lateral-distal-femoral angle (mLDFA), medial-proximal- tibial angle (MPTA), and joint-line-convergence angle previous limb injury people [62–65]. Nearly 46% of adults will develop painful KOA in at least one knee joint over their (JLCA) are also commonly used as the measurement param- lifetime [66]. By 2020, the KOA is predicted to become the eters [68]. The normal values of these angles are 85-90 deg, fourth leading cause of disability globally [67]. The etiology 85-90 deg, and 0-2 deg, respectively. The mLDFA greater than and progression of KOA are multifactorial, which includes 90 deg, MPTA less than 85 deg, or JLCA greater than 2 deg represent genu varum [71]. The mechanical axis deviation the increasing tibiofemoral force, the femoral shaft curvature Knee moment (Nm) Knee moment (Nm) Extension Extension Knee moment (Nm) Knee moment (Nm) Extension Extension Applied Bionics and Biomechanics 13 Table 12: Overview over the biomechanical eﬀects of KOA. Study Analysis Eﬀects Chao et al. [70] Medical radiology HKAA: ~178.8 deg for normal knee; <178 deg for MKOA patients mLDFA: 85-90 deg for normal knee; >90 deg for MKOA patients MPTA: 85-90 deg for normal knee; <85 deg for MKOA patients Paley [71] Medical radiology JLCA: 0-2 deg for normal knee; >2 deg for MKOA patients MAD: ~8 mm for normal knee; >8 mm for MKOA patients HKAA: ~177.7 deg for normal knee; ~174.2 deg for MKOA patients WBL ratio: ~41.4% for normal knee; ~24.2% for MKOA patients Medial joint apace: ~4.5 mm for normal knee; ~2.8 mm for Medical radiology MKOA patients Lateral joint apace: ~5.5 mm for normal knee; ~7.9 mm for Russell [50] MKOA patients Kinematics A lower knee ﬂexion angle for MKOA patients Kinetics A higher knee adduction moment for MKOA patients Muscles A lower quadriceps strength for MKOA patients A longer gait time, a smaller stride length and ROM, a greater knee Zhu et al. [72] Kinematics ﬂexion angle at heel strike, and an unobvious ﬂuctuation of knee ﬂexion angle in stand phase of walking for MKOA patients A slower walking speed, a shorter step length, a longer stance, and Kinematics double support time, and smaller cadence, stride length, and knee ROM for MKOA patients Alzahrani [73] The medial and lateral muscle cocontraction was increased for KOA Muscles patients Astephen et al. [74] Kinetics A greater knee adduction moment in mid-stance for MKOA patients A greater peak adduction moment during stair climbing for MKOA Guo et al. [75] Kinetics patients Rudolph et al. [76] and Schmitt A smaller peak knee ﬂexion moment during early and late stance Kinetics and Rudolph [77] phases for MKOA patients A 4-6 deg increase in varus alignment could increase around 70-90% Fitzgerald [78] Kinetics medial compartment load during single limb bearing Genu varum exceeding 5 deg was associated with greater functional Kinetics deterioration over 18 months than the value of 5 deg or less Lim et al. [79] No signiﬁcant relationship between the varus malalignment and the Muscles EMG ratio of VM and VL A 20% increase in the peak adduction moment could increase the KOA Kemp et al. [80] Kinetics progression risk Slemenda et al. [81], Hurley et al. Muscles A smaller quadriceps strength and muscle activation for KOA patients [82], and Oreilly et al. [83] The medial and lateral muscle cocontraction was increased for KOA Hubley-Kozey et al. [84] Muscles patients (MAD) is another measurement method. The normal MAD Zhu et al. [72] found that the KOA patients presented a longer is about 8 mm in the medial, and the value greater than the gait time, a smaller stride length and ROM, a greater knee ﬂexion angle at heel strike, and an unobvious ﬂuctuation of normal MAD represents genu varum [71]. Besides, the WBL ratio and medial or lateral joint space also used to characterize knee ﬂexion angle in the stand phase of walking. Alzahrani the KOA. Russell [50] pointed out that the WBL ratio, medial [73] indicated that the MKOA patients presented slower joint space, and lateral joint space were about 41.4%, 4.5 mm, walking speeds, shorter step lengths, longer stance and double and 5.5 mm for normal individuals and 24.2%, 2.8 mm and support time, and smaller cadence, stride length, and knee 7.9 mm for MKOA, respectively. In the knee kinematics ROM. In the knee kinetics aspect, Russell [50] described that aspect, Russell [50] reported that the knee ﬂexion pattern the knee adduction moment pattern was similar, but the mag- was similar, but the magnitude was lower for MKOA patients nitude was higher for MKOA patients compared to that for compared to that for normal subjects, as shown in Figure 7(b). normal subjects in walking, as shown in Figure 7(c). 14 Applied Bionics and Biomechanics 60 0.4 0.3 0.2 mLDFA HKAA 20 0.1 MPTA 0.0 020 40 60 80 100 0 20 40 60 80 100 MAD Time (% stance) Time (% stance) Health Health KOA KOA (a) (b) (c) Figure 7: The knee alignment measurement methods and the eﬀect of KOA on ﬂexion angle and adduction moment. (a) Sketch map of HKAA, mLDFA, MPTA, and MAD [61]. (b) Knee ﬂexion angles of health and KOA individuals [48]. (c) Knee adduction moments of health and KOA subjects [48]. Astephen et al. [74] observed that the knee adduction injuries to the ACL [89]. So, ACL injury will be mainly dis- moment in MKOA patients was greater than that in the nor- cussed in this section. mal in mid-stance. Guo et al. [75] found that the MKOA The biomechanical eﬀects of ACL were shown in patients possessed a greater peak adduction moment during Table 13. In the knee kinematics aspect, Zhao et al. [90] stair climbing. Rudolph et al. [76] and Schmitt and Rudolph reported that the knee ROM was lower for ACL-injured [77] pointed out that the peak knee ﬂexion moment in KOA patients in stair climbing. Slater et al. [91] pointed out that patients was smaller than that in the normal during early the peak knee ﬂexion angle was smaller and the peak knee adduction angle was greater for the ACL injury patients in and late stance phases. Fitzgerald et al. [78] reported that a 4-6 deg increase in varus alignment could increase around walking. Cronstrom et al. [92] represented that the knee 70-90% medial compartment load during single limb bear- adduction degree during weight-bearing activities for ACL- ing. Lim et al. [79] indicated that genu varum exceeding injured patients was greater in walking. Gao and Zheng 5 deg at baseline was associated with greater functional dete- [93] indicated that the ACL-injured patients had slower speed and smaller stride length during walking. In the knee rioration over 18 months than the value of 5 deg or less. Kemp et al. [80] observed that a 20% increase in the peak kinetics aspect, Alexander and Schwameder [94] observed a adduction moment could increase the KOA progression risk. 430% and 475% increase in the patella-femur contact force In the knee muscle aspect, Slemenda et al. [81], Hurley et al. for ACL-injured patients during upslope and downslope, [82], and Oreilly et al. [83] found that the KOA patients had respectively. Goerger et al. [95] found that the peak knee adduction moment during weight-bearing activities was smaller quadriceps strength and muscle activation. Lim et al. [79] indicated that there was no signiﬁcant relationship greater in patients after ACL than before injury. Slater et al. between the varus malalignment and the EMG ratio of [91] reported that a smaller peak external knee ﬂexion and VM and VL. Russell [50] reported that the medial muscle adduction moment can be found in the ACL-injured patients (VM-ST and VM-MG) and lateral muscle (VL-BF and during walking. Thomas and Palmieri-Smith [96] illustrated no diﬀerence in the external knee adduction moment among VL-LG) cocontraction indices were not signiﬁcantly diﬀerent between MKOA patients and normal person, but the quadri- individuals with ACL injury and those who are healthy. Nor- ceps strength was signiﬁcantly lower for MKOA patients. cross et al. [85] demonstrated that the ACL-injured patients Alzahrani [73] and Hubley-Kozey et al. [84] represented that had a greater knee energy adsorption during landing. the medial and lateral muscle cocontraction was increased Meniscus injury, as a sport-induced injury, is com- mon among athletes and general population [86, 89]. for the KOA patients. Knee ligament injury is a common and serious disease in The meniscus-injured patients are often coupled with trau- sport injuries and can signiﬁcantly change the biomechanics. matic ACL injury and can increase the stress and reduce According to where the injury hits, the knee ligament injury the stability of the knee joint during extension and ﬂexion can be divided into the ACL, PCL, TCL, FCL, and PL motions [89]. Many studies described that the secondary diseases, e.g., cartilage wear and KOA, can occur if not injuries. Many researchers pointed out that the secondary injuries, e.g., cartilage injury, meniscus injury, and KOA, treated in time [87, 88, 97]. According to the injured degree, can occur if not treated in time. And the ligament recon- diﬀerent treatments including conservative treatment, menis- struction, as a recognized eﬀective treatment, can dramati- cus suture, and meniscectomy, can be selected. cally recover the knee biomechanics [85–88]. In the ﬁve To our knowledge, there are rare research that study the biomechanical eﬀects of meniscus injury, as shown in types of injures, nearly half of ligament injuries are isolated Knee ﬂexion angle (deg) Knee adduction moment (Nm/kg·m) Applied Bionics and Biomechanics 15 Table 13: Overview over the biomechanical eﬀects of ACL and meniscus injury. Study Knee disorders Analysis Eﬀects Zhao et al. [90] ACL Kinematics A lower knee ROM during stair climbing for ACL-injured patients A greater knee adduction angle during weight-bearing activities for Gronstrom et al. [92] ACL Kinematics ACL-injured patients A slower speed and smaller stride length during walking for Gao and Zheng[93] ACL Kinematics ACL-injured patients A 430% and 475% increase in the patella-femur contact force during Alexander and Schwameder[94] ACL Kinetics upslope and downslope, respectively, for ACL-injured patients. A greater peak knee adduction moment during weight-bearing Goerger et al. [95] ACL Kinetics activities for ACL-injured patients A smaller peak knee ﬂexion angle and a greater peak knee adduction Kinematics angle during walking for ACL-injured patients Slater et al. [91] ACL Kinetics A smaller peak E-KFM and E-KAM for ACL-injured patients No diﬀerence in the E-KAM among individuals with ACL injury and Thomas et al. [96] ACL Kinetics those who are healthy Norcross et al. [85] ACL Kinetics A greater knee energy adsorption for ACL-injured patients A smaller walking speed and knee ROM and a larger cadence, step Magyar et al. [87] Meniscus injury Kinematics length, duration of support, and double support phase for meniscus injured patients A larger minimum ﬂexion angle and a smaller maximum Kinematics internal-external rotation angle for meniscus-injured patients Zhou [86] Meniscus injury A larger knee pressure and a smaller knee stressed area for Kinetics meniscus-injured patients Table 13. Magyar et al. [87] represented that the walking walking for several hours per day [98, 99, 102, 103]. The bio- speed and knee ROM of meniscus-injured patients were sig- mechanical eﬀects of SCI were shown in Table 14. Barbeau niﬁcantly smaller, and the cadence, step length, duration of et al. [104] pointed out that the knee ROM and peak knee- support, and double support phase of meniscus-injured swing-ﬂexion angle were lower, and peak knee moment was patients were remarkably larger in walking. Zhou [86] indi- larger for SCI patients in walking. Desrosiers et al. [105] found that the knee power was lower for SCI patients in cated that the maximum ﬂexion angle and maximum abduction-adduction angle between meniscus injury patients uphill and downhill walking. Pepin et al. [106] indicated that and healthy subjects have no apparent diﬀerence. The the SCI patients presented a longer ﬂexed knee at good con- meniscus-injured patients had a larger minimum ﬂexion tact and maintain the longer ﬂexion throughout the stance angle and a smaller maximum internal-external rotation phase of walking. angles in walking. And the knee stressed area was smaller Stroke, a common cerebrovascular disease, has a high and the knee pressure was larger for the meniscus-injured mortality and disability rate [107, 108]. There are about 7.0 patients in walking. million stroke survivals in China and 6.6 million in the United States [109, 110]. Stroke is known as the cause of paralysis, loss of motor function, paresis-weakness of muscle, 3.2.2. Knee Neurological Disorders and Its Biomechanical plegia-complete loss of muscle action, and muscle atrophy Eﬀects. SCI, one of the main causes of mobility disorders, [34, 108, 109]. Impaired walking and sit-stand transition aﬀects around 0.25-0.5 million people every year around are the main reason that poststroke patients cannot live inde- the world especially the young [98]. Approximately 43% of pendently [107, 108]. And about 30% of poststroke patients SCI patients turn out to have paraplegia and the number is have diﬃculty in ambulation without assistance [109]. Some increasing year by year [99]. The SCI patients are at an evidences showed that 70% of poststroke patients can recover increasing risk of many secondary medical complications, their walking capabilities by rehabilitation [108, 111]. The including muscle atrophy, pressure ulcer, bone density biomechanical eﬀects of stroke were shown in Table 14. reduction, and osteoporosis [100, 101]. Standing and walk- Sridar et al. [109] indicated that the kinematic and kinetic ing, as the most prevalent desires of these patients, can stim- performance of the poststroke patients will degrade, such as ulate blood circulation, ease muscle spasm, and increase the reduced walking speed, quadriceps muscle moment, and bone mineral density [98, 102]. Some evidences showed that quadriceps muscle power. Chen et al. [112] revealed that the SCI patients can reduce the secondary medical complica- the poststroke patients had lower knee ﬂexion in the swing tions risk and recover motion capabilities by standing or phase of walking. Stanhope et al. [113] found that the 16 Applied Bionics and Biomechanics Table 14: Overview over the biomechanical eﬀects of SCI, stroke, and CP. Study Knee disorders Analysis Eﬀects Kinematics A lower knee ROM and peak knee-swing-ﬂexion angle for SCI patients Barbeau et al. [102] SCI Kinetics A larger peak knee moment for SCI patients A lower knee power during uphill and downhill walking for SCI Desrosiers et al. [103] SCI Kinetics patients A longer knee ﬂexion at good contact and maintain the longer ﬂexion Pepin et al. [104] SCI Kinematics throughout the stance phase of walking for SCI patients. Kinematics A lower walking speed for stroke patients Sridar et al. [109] Stroke Muscles A lower quadriceps muscle moment and power for stroke patients A lower knee ﬂexion in the swing phase of walking for poststroke Chen et al. [112] Stroke Kinematics patients Post-stroke patients can compensate their poor knee ﬂexion in walking Stanhope et al. [113] Stroke Kinematics through faster speed A greater dynamic knee joint loading for stroke patients and no Marrocco et al. [114] Stroke Kinetics signiﬁcant diﬀerence between the E-KFM/E-KAM of stroke and healthy subjects. A less energy transference in mid-stance of walking and a lower energy Novak et al. [115] Stroke Kinetics absorption in the late stance of walking for stroke patients Crouch gait (characterized by excessive knee ﬂexion in stance phase), Lerner [19] and Thapa et al. [116] CP Kinetics walking ineﬃciency, and consumes much more energy Minimum knee ﬂexion angle during the stance phase exceeding 40 deg Hicks et al. [120] CP Kinematics for CP patients poststroke patients can compensate their poor knee ﬂexion in pain, and patellar stress fractures and then result in the walking through faster speed. Marrocco et al. [114] reported severity of crouch gait [19, 118, 121]. Some evidences a greater dynamic medical knee joint loading in stroke sub- showed that the mobility function can be preserved and jects in walking. However, the external knee adduction and the complications can be reduced by limiting excessive knee ﬂexion moments in walking were not signiﬁcantly diﬀerent ﬂexion in walking [118]. between the stroke patients and healthy subjects. Novak et al. [115] observed that less energy was transferred concen- trically via knee extensor muscles of stroke patients in mid- 4. Discussion and Conclusions stance of walking. And the stroke patients presented lower energy absorption by the knee extensors in the late stance Knee disorders, including musculoskeletal and neurological of walking. disorders, have serious inﬂuences on knee biomechanics. A CP, the most common pediatric neuromotor disorder, number of researches related with the biomechanics of nor- aﬀects around 0.2-0.3% live births [19, 116]. The injury in mal and diseased knee joint have been done during the last the central nervous system of the developing fetus or infant decades. Many advances have been made to understand the is the pathogenesis of CP, which eﬀects the control of move- kinematics and kinetics of normal and diseased knee during ment, balance, and posture [116, 117]. The person with CP diﬀerent common motions. In the aspect of normal knee bio- always has a variety of characteristics including rigidity, spas- mechanics, there is no clear assessment at the current state- ticity, abnormal aerobic and anaerobic capacity, decreased of-the-art. The diﬀerence between the results of diﬀerent muscle strength and endurance, abnormal muscle tone, researches is signiﬁcant. In the aspect of diseased knee bio- deformities, and muscle weakness [19, 118, 119]. The biome- mechanics, a lower knee ﬂexion angle, walking speed, mus- chanical eﬀects of CP were shown in Table 14. Crouch gait, cles strength, and a higher knee contact pressure were characterized by excessive knee ﬂexion in stance phase, is a always observed. Understanding how pathologies aﬀect the frequent gait deviation in CP patients [19, 117, 118]. Hicks knee joint biomechanics is important for designing knee et al. [120] reported the minimum knee ﬂexion angle during assistive devices and optimizing rehabilitation exercise pro- the stance phase exceed 40 deg for the CP patients. Com- gram. However, the current understanding still has not met pared with the normal gait, crouch gait is ineﬃcient and the requirement of a designer and rehabilitative physician. consumes much more energy [19, 116]. For maintaining And it is hard to ﬁnd a research that can systematic study the excessive knee ﬂexion posture in walking, the stress of all aspects of knee biomechanics completely. Thus, deeper the knee and surrounding muscles are increasing, which understanding of the biomechanics of normal and diseased can lead to bony deformities, degenerative arthritis, joint knee joint will still be an urgent need in the future. Applied Bionics and Biomechanics 17 Some limitations of the current studies must be noted. [3] K. Shamaei, M. Cenciarini, A. A. Adams, K. N. Gregorczyk, J. M. Schiﬀman, and A. M. 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Publisher: Hindawi Publishing Corporation
Copyright: Copyright © 2020 Li Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ISSN: 1176-2322
eISSN: 1754-2103
DOI: 10.1155/2020/7451683
Publisher site: See Article on Publisher Site

Abstract

Hindawi Applied Bionics and Biomechanics Volume 2020, Article ID 7451683, 22 pages https://doi.org/10.1155/2020/7451683 Review Article Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review 1 1 1 1 1 2 Li Zhang , Geng Liu , Bing Han , Zhe Wang , Yuzhou Yan , Jianbing Ma , and Pingping Wei Shaanxi Engineering Laboratory for Transmissions and Controls, Northwestern Polytechnical University, Xi'an 710072, China Hong-Hui hospital, Xi’an Jiaotong University College of Medicine, Xi'an 710054, China State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi'an 710054, China Correspondence should be addressed to Geng Liu; npuliug@nwpu.edu.cn Received 8 November 2019; Accepted 1 February 2020; Published 4 April 2020 Academic Editor: Stefano Zaﬀagnini Copyright © 2020 Li Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The knee joint, as the main lower limb motor joint, is the most vulnerable and susceptible joint. The knee injuries considerably impact the normal living ability and mental health of patients. Understanding the biomechanics of a normal and diseased knee joint is in urgent need for designing knee assistive devices and optimizing a rehabilitation exercise program. In this paper, we systematically searched electronic databases (from 2000 to November 2019) including ScienceDirect, Web of Science, PubMed, Google Scholar, and IEEE/IET Electronic Library for potentially relevant articles. After duplicates were removed and inclusion criteria applied to the titles, abstracts, and full text, 138 articles remained for review. The selected articles were divided into two groups to be analyzed. Firstly, the real movement of a normal knee joint and the normal knee biomechanics of four kinds of daily motions in the sagittal and coronal planes, which include normal walking, running, stair climbing, and sit-to-stand, were discussed and analyzed. Secondly, an overview of the current knowledge on the movement biomechanical eﬀects of common knee musculoskeletal disorders and knee neurological disorders were provided. Finally, a discussion of the existing problems in the current studies and some recommendation for future research were presented. In general, this review reveals that there is no clear assessment about the biomechanics of normal and diseased knee joints at the current state of the art. The biomechanics properties could be signiﬁcantly aﬀected by knee musculoskeletal or neurological disorders. Deeper understanding of the biomechanics of the normal and diseased knee joint will still be an urgent need in the future. 1. Introduction knee to withstand tremendous forces during various normal movements [1]. Therefore, it is an urgent need to study the Since the number of the old and obese worldwide has been movement biomechanics of the normal and diseased knee increasing yearly, the research on human motion dysfunc- joint for the assistance or rehabilitation of human locomo- tion is getting more and more attention. The knee joint, as tor function. the main lower limb motor joint, is the most vulnerable In the last decade, several related review papers appeared and susceptible joint [1]. Knee impairments are the com- and could be divided into two aspects, normal knee biome- mon physical problems which impact the normal living chanics and diseased knee biomechanics. For the former, ability and mental health of these patients [2]. The inﬂu- Masouros et al. [5] analyzed the knee kinematics and ences mainly contain the supporting body weight, the assist- mechanic and surrounding soft tissue in detail. The research ing lower limb swing, and the absorbing strike shock [3]. pointed out that the knowledge of these structures was very useful for the diagnosis and evaluations of treatment. Wang The movement biomechanics, as an important branch of biomechanics, studies the coordination of the bones, mus- et al. [6] reviewed the modeling and simulation methods of cles, ligament, and tendons in various human movements human musculoskeletal systems. The knee kinematics and [4]. The complex interaction of these structures allows the kinetics in six common motions including walking, jogging, 2 Applied Bionics and Biomechanics stair ascent, stair descent, squatting, and kneeling were dis- 2. Methods cussed. Chhabra et al. [1] reported the anatomic structures This review was conducted in accordance with Preferred and their relationships in the uninjured knee joint, which Reporting Items for Systematic Reviews and Meta-Analyses provided the critical guidance for the reconstruction of the (PRISMA) [11]. We systematically searched electronic data- multiple ligament injured knee joint. Madeti et al. [4] dis- bases including ScienceDirect, Web of Science, PubMed, cussed various model formulations of the knee joint, includ- Google Scholar, and IEEE/IET Electronic Library for poten- ing mathematical, two-dimensional, and three-dimensional tially relevant articles. The following terms were used as key- models. And the forces acting on the knee joint had also words (identical for all databases): “knee joint,”“gait,”“knee been compared. For the latter, Flandry et al. [7] provided biomechanics,”“knee disease,” and “sports biomechanics.” an overview of the surgical anatomy of the knee joint and Given the fast advancement in acquisition equipment and emphasized connective tissue structures and common injury theoretical research of knee biomechanics, the search time patterns. Woo et al. [8] reviewed the biological and biome- range was set from 2000 to November 2019. A total of 1787 chanical knowledge of normal knee ligaments, as well as articles were retrieved initially. The daily life activities were the anatomical, biological, and functional perspectives of mainly considered in this review, the articles about more the current reconstruction knowledge following knee liga- complex activities, such as squats, hops, cut manoeuvres, ment injuries. The research also provided guidance for were excluded. After 679 articles were excluded, 1108 articles improving the treatment of knee ligament injuries. Louw about daily life activities were selected. In addition, review of et al. [9] assessed the eﬀects of the occluded vision on the all references cited by the selected articles and more insight knee kinematics and kinetics during functional activities, into other relevant authors’ studies yielded an additional 35 such as squatting, stepping down, drop landing, hopping, articles for possible inclusion. Then, all selected articles were and cutting movements in healthy individuals and the input into Excel to eliminate duplicates. After 511 duplicates individuals with anterior cruciate ligament injury or recon- were removed, 632 articles were assessed for inclusion. struction. Sosdian et al. [10] discussed the eﬀects of knee Studies were considered eligible if they met the following arthroplasty on the kinematics and kinetic properties of inclusion criteria: normal knee kinematics related, normal the frontal plane and sagittal plane during the stance knee dynamics related, diseased knee kinematics related, dis- phase of normal walking. The results showed that the peak eased knee dynamics related, English, and full-text articles. knee adduction angle and moment were decreased, but the Two reviewers (LZ and ZW) independently assessed the title peak knee ﬂexion moment was increased after knee and abstracts of the potential studies. After an initial deci- arthroplasty. However, to our knowledge, there is no sion, the full text of the studies that potentially met the review that synthesized the literature discussing the move- inclusion criteria were assessed before a ﬁnal decision was ment biomechanics of both the normal and the diseased made. A senior reviewer (GL) was consulted in cases involv- knee joint. ing disagreement. After exclusion of irrelevant titles and Understanding the knee biomechanics is a prerequisite screening of abstracts, 203 articles remained. Subsequently, for designing knee assistive devices and optimizing rehabil- detailed full-text screening based on the inclusion criteria itation exercises. This paper provides an overview of the was carried out, and 65 articles were excluded. Finally, 138 current biomechanical knowledge on normal and injured full-text articles were examined for full review. The search knee joints. For better assessment of the function of the process is demonstrated using the following diagram shown knee joint, the biomechanical parameters including angle, in Figure 1. moment, power, and stiﬀness from various researchers in diﬀerent daily motions are reviewed and compared. For 3. Results better understanding the kinematics and kinetics of real knee movement, the polycentric rotation in the sagittal We divided the 138 selected articles, which fulﬁlled the liter- plane and biomechanics in the coronal plane are also dis- ature search inclusion criteria, into two groups: biomechani- cussed. Further, the common knee disorders including cal properties of normal knee joint and biomechanical musculoskeletal and neurological disorders and their properties of diseased knee joint. For the former, the real inﬂuences on the knee biomechanics are also reviewed movement of a normal knee joint and the normal knee bio- and discussed. We hypothesized that the comprehensive mechanics of four kinds of daily motions in the sagittal and understanding of the knee joint biomechanics in physiolog- coronal planes, which include normal walking, running, ical and pathological conditions could signiﬁcantly improve stair climbing, and sit-to-stand, were discussed and ana- the design of knee assistive devices and rehabilitation lyzed. For the latter, an overview of the current knowledge exercise programs. on the movement biomechanical eﬀects of common knee The rest of this paper is organized as follows. In Section 2, musculoskeletal disorders (KOA) and knee neurological the search strategies adopted for the literature review are disorders (SCI, stroke, and CP) were provided. provided. In Section 3, the selected literatures including the biomechanical properties of normal knee joint and 3.1. Biomechanical Properties of Normal Knee Joint the knee diseased eﬀects on the biomechanics are summa- rized. In Section 4, the limitations of the current studies 3.1.1. Knee Biomechanics of Daily Motions in Sagittal Plane. are brieﬂy discussed and the recommendations for future Walking, running, stair climbing, and sit-to-stand are very research are provided. frequent motions in human’s daily life. In all of the motions, Applied Bionics and Biomechanics 3 Records indentiﬁed through Additional records identiﬁed database searching through other sources (n = 1787) (n = 38) Complex activities excluded (n = 679) Selected articles (n = 1108) Duplicates removed (n = 1143) Records excluded (n = 511) Title and abstract review (n = 632) Title and abstract excluded, with reasons (n = 429) Full-text articles for eligibility (n = 203) Full-text articles excluded, with reasons (n = 65) Studies included in systematic review (n = 138) Figure 1: The PRISMA ﬂow diagram of study selection process. the main functions of the knee joint include supporting points A, B, C, and D are from 6 to 28 deg, -2 to 5 deg, 53 to 78 deg, and -5 to 16 deg, respectively. In general, the the body weight (BW), absorbing shock of heel strikes, and assisting lower limbs swing [3]. According to the pre- ROM is around 53 to 75 deg for normal walking. vious researches, the passive knee ﬂexion could reach Figure 2(c) shows the typical knee moment-time curve. There 160 deg in the sagittal plane [1, 5, 12]. The peak load are two peak extension (E and G) and ﬂexion (F and H) through the knee joint is 2-3 BW during walking, 2-5 moments. Point H occurs in the swing phase and the others BW during sit-stand-sit, 4-6 BW during stair climbing, occur in the stance phase. Table 2 gives the values of these and 7-12 BW during running [12–14]. In this section, the points from 11 studies. The values of these points vary consid- ROM, maximum moment, maximum power, and stiﬀness erably between diﬀerent studies. The ranges of points E, F, G, of the knee joint are mainly discussed because they are the and H are from 0.129 to 0.945 Nm/kg, -0.675 to 0.067 Nm/kg, key indexes for the design of knee assistive device and opti- 0.101 to 0.466 Nm/kg, and -0.420 to 0.086 Nm/kg, respec- mization of rehabilitation exercises. tively. The ﬁrst peak extension moment is always greater than As shown in Figure 2(a), the walking gait can be divided the second. But it is hard to determine who is bigger between into two main phases: stance (about 0-65% of gait) and swing the two peak ﬂexion moments. In general, the range of moment is about 0.458 to 1.265 Nm/kg for normal walking. phases (about 65-100% of gait) [15, 16]. The stance phase consists of three subphases: initial (heel strike to foot ﬂat), Figure 2(d) shows the typical knee power-time curve. It middle (foot ﬂat to opposite heel strike), and terminal stance includes one peak generation power (J) and three peak (opposite heel strike to toe oﬀ) [16, 17]. The knee joint in the absorption powers (I, K, and L). Point L occurs in the swing stance phase is regarded as a shock damping mechanism to phase and the others occur in the stance phase. For the knee joint, there is only absorption power in the swing phase. accept the BW [18]. The swing phase consists of two sub- phases: initial (toe oﬀ to knee maximum ﬂexion) and termi- And in the whole gait cycle, knee absorption powers are much nal swing (knee maximum ﬂexion to heel strike) [16, 17]. larger than generation powers. Mooney and Herr [22] found The main function of the knee in the swing phase is assisting that the mean net knee power is about -18 W (mean genera- ﬂexion-extension for toe clearance, foot placement, and tak- tion and absorption power is about 18 W and -36 W, respec- tively). Table 3 gives the values of these points from 10 ing over the load in the next step [19, 20]. Zheng [21] reported that the knee biomechanics is aﬀected mainly by studies. The ranges of points I, J, K, and L are from -1.736 walking speed. With the speed increased, the ROM, maxi- to -0.116 W/kg, 0.286 to 0.834 W/kg, -1.935 to -0.403 W/kg, mum extension moment, and maximum absorption power and -2.712 to -0.321 W/kg, respectively. In general, the range would increase. Figure 2(b) shows the typical knee angle- of power is about 1.035 to 3.214 W/kg for normal walking. As shown in Figure 3(a), the running cycle can be divided time curve. There are two peak ﬂexion (A and C) and exten- sion (B and D) angles. Points A and B occur in the stance into four main phases: stance (heel strike to toe oﬀ), ﬁrst ﬂoat phase, and C and D occur in the swing phase. Comparing (toe oﬀ to opposite heel strike), swing (opposite heel strike to the two peak ﬂexion angles, the value in the swing phase is opposite toe oﬀ), and second ﬂoat phases (opposite toe oﬀ to always greater than that in the stance phase. Table 1 gives heel strike) [14]. The knee main function in running is simi- lar to that in walking. Comparing Figures 2 and 3, it can be the values of these points from 18 studies. The ranges of Included Eligibility Screening Identiﬁcation 4 Applied Bionics and Biomechanics Stance (65%) Swing (35%) Initial Middle Terminal Initial Terminal B D 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) –150 –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 2: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a walking gait cycle. (a) Sketch map of walking motion [14]. (b) Knee angle-time curve ((A) ﬁrst peak knee ﬂexion angle, (B) ﬁrst peak knee extension angle, (C) second peak knee ﬂexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee absorption power, (J) ﬁrst peak knee generation power, (K) second peak knee absorption power, and (L) third peak knee absorption power) [16, 17]. Table 1: Overview over the experimental results of knee angle for normal walking. Subjects (mean height ± SD (m), ° ° ° ° ° ° Study Speed (m/s) A ()B()C()D( ) C-A ( ) ROM ( ) mean weight ± SD (kg)) Collins et al. [125] 9 (1:84 ± 0:10, 77:4±9:2) 1.25 12 3 61 -5 49 66 Zheng [21] 1 (1.78, 70) 1.2 22 10 66 6 44 60 Wang [126], Lee et al. [17] 1 (1.69, 63.5) 1.5 7 3 53 -2 46 55 Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 28 5 78 4 50 74 Shamaei et al. [3, 127] 3 (1:76 ± 0:75, 68:6±2:2) 1.25 26 15 69 6 43 63 Blazkiewicz [128] 1 (1.85, 80) — 10 -2 53 0 43 55 Sridar et al. [34] 3 (1:70 ± 0:05, 74:7±8:4) 1.0 22 11 62 2 40 60 Knaepen et al. [129] 10 (1:82 ± 0:10, 77:5±11:7) 0.69 14 8 62 8 48 54 Shirota et al. [130] 4 (1:80 ± 0:08, 74 ± 6:8) 1.24 13 5 65 1 52 64 Gordon et al. [131] 3 (1:80 ± 0:01, 96 ± 9) 1.0 6 0 55 16 49 55 Ding et al. [132] 8 (1:76 ± 0:06, 78:5±9:9) 1.25 24 7 75 0 51 75 Winter [133], Li et al. [134] 1 (—, 58) 1.3 16 5 67 -2 51 69 Beyl et al. [135] —— 22 8 64 1 42 63 Baliunas et al. [136] 15 (1:68 ± 0:12, 74 ± 16) 0.98 17 3 60 -2 43 62 Yang et al. [137] 1 (1.75, 70) 1.0 14 3 56 6 42 53 A: ﬁrst peak knee ﬂexion angle; B: ﬁrst peak knee extension angle; C: second peak knee ﬂexion angle; D: second peak knee extension angle. Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 5 Table 2: Overview over the experimental results of knee moment for normal walking. Subjects (mean height ± SD (m), Speed E F G H E-G F-H Range Study mean weight ± SD(kg)) (m/s) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) Collins et al. [125] 9 (1:84 ± 0:10, 77:4±9:2) 1.25 0.556 -0.245 0.207 -0.388 0.349 0.143 0.944 Shamaei et al. [3] 3 (1:76 ± 0:75, 68:6±2:2) 1.25 0.335 -0.248 0.102 -0.379 0.233 0.131 0.714 Zheng [21] 1 (1.78, 70) 1.2 0.571 -0.171 0.114 0.086 0.457 -0.257 0.742 Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 0.766 -0.344 0.189 -0.378 0.577 0.034 1.144 Blazkiewicz [128] 1 (1.85, 80) — 0.263 -0.675 0.225 -0.063 0.038 -0.612 0.938 Ding et al. [132] 8 (1:76 ± 0:06, 78:5±9:9) 1.25 0.777 -0.204 0.204 -0.420 0.573 0.198 1.197 Winter [133], Li et al. [134] 1 (—, 58) 1.3 0.517 -0.155 0.189 -0.224 0.328 0.069 0.741 Yang et al. [137] 1 (1.75, 70) 1.0 0.129 -0.329 0.101 -0.257 0.028 -0.072 0.458 Dijk et al. [138] 8 (1:79 ± 0:04, 75:1±6:5) 1.11 0.945 0.067 0.466 -0.320 0.479 -0.387 1.265 Briggs et al. [51] 20 (1:67 ± 0:11, 58:0±12:6) — 0.534 -0.276 0.190 — 0.344 —— E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. Table 3: Overview over the experimental results of knee power for normal walking. Subjects (mean height ± SD (m), Study Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg) mean weight ± SD (kg)) Collins et al. [125] 9 (1:84 ± 0:10, 77:4± 9:2) 1.25 -0.571 0.286 -1.057 -1.457 1.743 Zheng [21] 1 (1.78, 70) 1.2 -0.489 0.591 -0.469 -0.321 1.080 Mooney et al. [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 -0.889 0.834 -1.334 -1.639 2.473 Malcolm et al. [16] 8 (1:67 ± 0:02, 60 ± 1) 1.38 -1.736 0.502 -0.763 -2.712 3.214 Ding et al. [132] 8 (1:76 ± 0:06, 78:5± 9:9) 1.25 -0.968 0.606 -1.290 -1.677 2.283 Winter [133], Li et al. [134] 1 (—, 58) 1.3 -0.755 0.324 -0.924 -1.247 1.571 Yang et al. [137] 1 (1.75, 70) 1.0 -0.116 0.296 -0.403 -0.739 1.035 Dijk et al. [138] 8 (1:79 ± 0:04, 75:1± 6:5) 1.1 -1.242 0.586 -1.509 -1.329 2.095 Walsh et al. [139] 1 (—, 60) 0.8 -0.828 0.667 -1.935 -1.410 2.602 I: ﬁrst peak knee absorption power; J: ﬁrst peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power. observed that the curves of angle, moment, and power in As shown in Figure 4(a), the stair climbing cycle (includ- ing stair ascent and descent) can be divided into two main running are also similar to that in walking. Hamner and Delp [23] reported that the knee biomechanics is mainly aﬀected phases: stance phase (about 0-62% of the cycle) and swing by running speed. With increasing speed, the ROM, maxi- phase (about 62-100% of the cycle) [24, 25]. The stance phase mum extension moment, and maximum absorption power consists of three subphases: initial (foot contact to opposite would increase. Figure 3(b) shows the typical knee angle- toe oﬀ), middle (opposite toe oﬀ to opposite foot contact), time curve in a gait cycle and Table 4 gives the angles of and terminal stance (opposite foot contact to toe oﬀ) points A, B, C, and D from 7 studies. The ranges of points [24, 26, 27]. Riener et al. [24] indicated that the knee bio- A, B, C, and D are from 36 to 60 deg, 13 to 29 deg, 80 to mechanics is mainly aﬀected by the rate of leg length and 129 deg, and 10 to 21 deg, respectively. In general, the ROM stair height. Figure 4(b) shows the typical knee angle-time of the knee joint is around 60 to 115 deg for running. curves in a stair ascent and stair descent cycle. They all Figure 3(c) shows the typical knee moment-time curve in a include one peak ﬂexion (A) and extension (B) angle. For running cycle and Table 5 gives the moments of points E, stair ascent, point A occurs in the swing phase and B occurs F, G, and H from 5 studies. The ranges of points E, F, G, in the terminal stance phase. And for stair descent, point A and H are from 1.157 to 2.574 Nm/kg, -0.259 to 0.320 Nm/kg, occurs in the terminal stance phase and B occurs in the swing 0.135 to 0.585 Nm/kg, and -1.474 to -0.277 Nm/kg, respec- phase. Table 7 gives the values of these points from 7 studies. tively. The range of moment is about 1.434 to 3.904 Nm/kg The ranges of points A and B are from 83 to 102 deg and 0 to for running. Figure 3(d) shows the typical knee power-time 11 deg for stair ascent and from 83 to 105 deg and 1 to 19 deg curve in a running cycle and Table 6 gives the powers of points for stair descent, respectively. In general, the ROM of the knee joint is around 78 to 94 deg for stair ascent and 76 to I, J, K, and L from 6 studies. The ranges of points I, J, K, and L are from -1.706 to -12.567 W/kg, 2.739 to 9.405 W/kg, -3.456 90 deg for stair descent. Figure 4(c) shows the typical knee to -1.525 W/kg, and -3.456 to -6.732 W/kg, respectively. The moment-time curves in a stair ascent and descent cycle. range of power is about 8.724 to 21.972 W/kg. This empha- They all include two peak extension (E and G) and ﬂexion sizes that the ranges of knee angle, moment, and power in (F and H) moments. For stair ascent, points E and F occur in the stance phase and G and H occur in the swing running are far more than those in normal walking. 6 Applied Bionics and Biomechanics B D Float Float Stance (40%) Swing (30%) (15%) (15%) 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) –150 I K –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 3: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a running cycle. (a) Sketch map of running motion [14]. (b) Knee angle-time curve ((A) ﬁrst peak knee ﬂexion angle, (B) ﬁrst peak knee extension angle, (C) second peak knee ﬂexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee absorption power, (J) ﬁrst peak knee generation power, (K) second peak knee absorption power, and (L) third peak knee absorption power) [23, 122, 123]. Table 4: Overview over the experimental results of knee angle for running. Subjects (mean height ± SD (m), ° ° ° ° ° ° Study Speed (m/s) A ()B()C()D( ) C-A ( ) ROM ( ) mean weight ± SD (kg)) 2.1 36 22 80 20 44 60 Zheng [21] 1 (1.78, 70) 2.8 49 20 90 17 41 73 2.0 42 18 85 11 43 74 3.0 44 16 103 12 59 91 Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9±7:0) 4.0 46 15 119 13 73 106 5.0 47 15 129 14 82 115 Dollar et and Herr[122] 1 (—, 85) 3.2 43 23 89 21 46 68 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 44 15 105 13 61 92 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8± 11) 2.48 48 17 86 10 38 76 Miller et al. [141] 12 (1:66 ± 0:05, 61 ± 4:7) 3.8 60 29 96 16 36 80 Ferber et al. [52] 20 (1:81 ± 0:06, 82:3±11:8) 3.65 46 13 —— — — A: ﬁrst peak knee ﬂexion angle; B: ﬁrst peak knee extension angle; C: second peak knee ﬂexion angle; D: second peak knee extension angle. phase. And for stair descent, points E, F, and G occur in the to -0.145 Nm/kg, 0.027 to 0.144 Nm/kg, and -0.314 to stance phase and H occurs in the swing phase. Table 8 gives -0.121 Nm/kg for stair ascent and from 0.007 to 1.512 Nm/kg, the values of these points from 7 studies. The ranges of points -0.070 to 0.662 Nm/kg, 0.365 to 1.620 Nm/kg, and -0.266 E, F, G, and H are from 0.454 to 1.409 Nm/kg, -0.556 to 0.040 Nm/kg for stair descent, respectively. In general, Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 7 Table 5: Overview over the experimental results of knee moment for running. Subjects (mean height ± SD (m), Speed E F G H E-G F-H Range Study mean weight ± SD (kg)) (m/s) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) 2.1 1.157 -0.030 0.274 -0.277 0.883 0.247 1.434 Zheng [21] 1 (1.78, 70) 2.8 1.749 0.320 0.320 -0.351 1.429 0.671 2.100 2.0 1.798 -0.205 0.135 -0.697 1.663 0.492 2.495 3.0 2.159 -0.226 0.269 -0.925 1.890 0.699 3.084 Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9±7:0) 4.0 2.402 -0.233 0.405 -1.147 1.997 0.914 3.549 5.0 2.430 -0.259 0.585 -1.474 1.845 1.215 3.904 Dollar and Herr [122] 1 (—, 85) 3.2 1.571 0.175 0.175 -0.591 1.396 0.766 2.162 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 2.196 -0.249 0.248 -0.775 1.948 0.526 2.971 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8±11) 2.48 2.574 -0.221 0.307 -0.649 2.267 0.428 3.223 E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. Table 6: Overview over the experimental results of knee power for running. Subjects (mean height ± SD (m), Study Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg) mean weight ± SD (kg)) 2.1 -5.859 4.336 -2.231 -3.521 10.195 Zheng [21] 1 (1.78, 70) 2.8 -8.008 7.386 -3.456 -3.456 15.394 Dollar and Herr [122] 1 (—, 85) 3.2 -1.706 4.766 -1.525 -3.958 8.724 Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 -9.013 4.539 -2.439 -6.732 13.552 Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8±11) 2.48 -12.567 9.405 -2.371 -4.473 21.972 Ferber et al. [52] 20 (1:81 ± 0:06, 82:3±11:8) 3.65 -5.462 2.739 —— — Heiderscheit et al. [62] 45 (1:76 ± 0:10, 69:5±13:1) 2.9 -6.948 5.422 —— — I: ﬁrst peak knee absorption power; J: ﬁrst peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power. the range of moment is about 1.010 to 1.815 Nm/kg for stair 6 studies. The ranges of points A and B are from 82 to ascent and 0.435 to 1.815 Nm/kg for stair descent. Figure 4(d) 96 deg and -3 to 22 deg, respectively. In general, the ROM of the knee joint is around 60 to 87 deg for sit-to-stand cycle. shows the typical knee power-time curves in a stair ascent and descent cycle. They all include two peak generation Table 11 gives the experimental results of knee moment from (I and K) and absorption (J and L) powers. For stair ascent, 9 studies. The ranges of points E and F are from 0.619 to the whole curve lies in the generation area mostly. And for 2.187 Nm/kg and -0.198 to 0.609 Nm/kg, respectively. In gen- stair descent, the whole curve lies in the absorption area eral, the range of moment is about 0.619 to 1.578 Nm/kg for mostly. Table 9 gives the values of these points from 4 stud- sit-to-stand cycle. The researchers about knee power in sit- ies. The ranges of points I, J, K, and L are from -1.044 to to-stand is rare, and only two researchers have been found. 2.887 W/kg, -0.228 to 0.071 W/kg, 0.447 to 1.020 W/kg, and Spyropoulos et al. [29] reported that the knee power was -0.739 to -0.265 W/kg for stair ascent and from -0.212 to about 1.973 W/kg for sit-to-stand. But Kamali et al. [30] 0.569 Nm/kg, -3.621 to -0.248 Nm/kg, -1.326 to -0.429, and pointed out that the value was about 0.560 W/kg for -5.485 to -2.077 Nm/kg for stair descent, respectively. In sit-to-stand. general, the range of power is about 1.309 to 3.481 W/kg for Because of the complicated interaction of the underlying stair ascent and 2.114 to 6.054 W/kg for stair descent. biological mechanisms, the knee joint demonstrates a spring- As shown in Figure 5(a), the sit-to-stand begins in a sit like behavior in common motions [31–33]. Figure 6 shows posture and ends in a stand posture. Figures 5(b)–5(d) show the typical knee moment-angle curves in the sagittal plane. the typical knee angle-time, moment-time, and power-time A linear relationship can be seen during the sit-to-stand, curves in sit-to-stand cycle, respectively. For the knee joint, and the weight acceptance and swing phase of walking, run- there are only extension angle, extension moment, and ning, and stair climbing. Quasistiﬀness refers to the slope of the linear ﬁt to the knee moment-angle curve [33]. During generation power in the whole sit-to-stand movement. The maximum angle, moment, and power occur in nearly the walking, running, and stair climbing, a high stiﬀness in the same time that the buttocks leave the chair. Hurley et al. weight acceptance phase and a low stiﬀness in the swing [28] represented that the biomechanics of knee joint is phase can be observed. For walking, Zhu et al. [20] and Wang mainly aﬀected by the rate of leg length and chair height. [12] found that the knee quasistiﬀness was around 3.0 and 2.27 Nm/deg in the stand phase. Sridar et al. [34] indicated Table 10 gives the experimental results of knee angle from 8 Applied Bionics and Biomechanics 100 AA Descent Stance (62%) Swing (38%) Initial Middle Terminal Ascent 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) (a) (b) 120 G Descent Ascent –150 J Ascent Descent L –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% stribe period) Time (% stribe period) (c) (d) Figure 4: A sketch map of motion and the typical curves of knee angle, moment, and power in sagittal plane for stair ascent and stair descent. (a) Sketch map of the stair ascent and stair descent motion. (b) Knee angle-time curve ((A) peak knee ﬂexion angle and (B) peak knee extension angle. (c) Knee moment-time curve ((E) ﬁrst peak knee extension moment, (F) ﬁrst peak knee ﬂexion moment, (G) second peak knee extension moment, and (H) second peak knee ﬂexion moment). (d) Knee power-time curve ((I) ﬁrst peak knee generation power, (J) ﬁrst peak knee absorption power, (K) second peak knee generation power, and (L) second peak knee absorption power) [24, 25]. Table 7: Overview over the experimental results of knee angle for stair ascent and stair descent. Subjects (mean height ± SD (m), ° ° ° Study Riser × tread (cm × cm) Type A ()B( ) ROM ( ) mean weight ± SD (kg)) Ascent 91 9 82 13:8×31:0 Descent 89 13 76 Ascent 95 9 86 17:0×29:0 Riener et al. [24], Joudzadeh et al. [25] 10 (1:79 ± 0:05, 82:2±8:5) Descent 93 15 78 Ascent 102 10 92 22:5×25:0 Descent 102 13 89 Ascent 99 11 88 22:0×28:0 Mcfadyen and Winter [142] 3 (—, —) Descent 105 19 86 Ascent 89 7 82 18:0×28:0 Zhang et al. [143] 10 (1:74 ± 0:05, 72:7±8:6) Descent 96 10 86 Ascent 83 5 78 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) Descent 83 6 77 Ascent 94 0 94 18:0×28:5 Protopapadaki et al. [144] 33 (1:69 ± 0:08, 67:5±12:1) Descent 91 1 90 Ascent 95 11 84 17:0×28:0 Law [26] 19 (1:64 ± 0:08, 59:5±7:8) Descent 93 3 90 A: peak knee ﬂexion angle; B: peak knee extension angle. Knee moment (Nm) Extension Knee angle (deg) Knee power (W) Flexion Generation Applied Bionics and Biomechanics 9 Table 8: Overview over the experimental results of knee moment for stair ascent and stair descent. Subjects (mean height ± SD (m), Riser × tread E F G H E-G F-H Range Study Type mean weight ± SD (kg)) (cm × cm) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) (Nm/kg) Ascent 1.055 -0.179 0.027 -0.183 1.028 0.004 1.238 13:8×31:0 Descent 0.916 0.587 1.247 -0.096 -0.331 0.683 1.343 Ascent 1.093 -0.218 0.042 -0.177 1.051 -0.041 1.311 Riener et al. [24] and Joudzadeh 17:0×29:0 10 (1:79 ± 0:05, 82:2±8:5) et al. [25] Descent 1.006 0.662 1.345 -0.091 -0.339 0.753 1.436 Ascent 1.164 -0.247 0.037 -0.172 1.127 0.075 1.411 22:5×25:0 Descent 0.991 0.653 1.470 -0.088 -0.479 0.741 1.558 Ascent 1.409 -0.406 0.164 -0.314 1.245 -0.092 1.815 22:0×28:0 Mcfadyen and Winter[142] 3 (—, —) Descent 1.512 0.405 1.620 -0.266 -0.108 0.671 1.886 Ascent 0.588 -0.493 0.144 -0.256 0.444 -0.237 1.081 18:0×28:0 Zhang et al. [143] 10 (1:74 ± 0:05, 72:7±8:6) Descent 0.338 0.152 1.106 -0.201 -0.768 0.353 1.307 Ascent 0.921 -0.456 0.043 -0.206 0.878 -0.250 1.377 ± 14) 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 Descent 0.448 0.263 1.012 -0.167 -0.564 0.430 1.179 Ascent 0.454 -0.556 0.032 -0.121 0.422 -0.435 1.010 18:0×28:5 Protopapadaki et al. [144] 33 (1:69 ± 0:08, 67:5±12:1) Descent 0.007 -0.070 0.365 -0.040 -0.358 -0.030 0.435 Ascent 0.899 -0.145 0.046 -0.147 0.085 0.002 1.036 17:0×28:0 Law [26] 19 (1:64 ± 0:08, 59:5±7:8) Descent 0.603 0.439 1.006 -0.076 -0.403 0.515 1.082 E: ﬁrst peak knee extension moment; F: ﬁrst peak knee ﬂexion moment; G: second peak knee extension moment; H: second peak knee ﬂexion moment. 10 Applied Bionics and Biomechanics Table 9: Overview over the experimental results of knee power for stair ascent and stair descent. Subjects (mean height ± SD (m), Riser × tread I J K L Range Study Type mean weight ± SD (kg)) (cm × cm) (W/kg) (W/kg) (W/kg) (W/kg) (W/kg0 Ascent 2.322 0.071 0.647 -0.309 2.631 13:8×31:0 Descent 0.256 -0.678 -0.429 -3.788 4.044 Ascent 2.538 0.055 0.696 -0.312 2.850 Riener et al. [24] and 17:0×29:0 10 (1:79 ± 0:05, 82:2±8:5) Joudzadeh et al. [25] Descent 0.305 -1.029 -0.453 -4.141 4.446 Ascent 2.887 0.049 0.811 -0.288 3.175 22:5×25:0 Descent -0.212 -1.255 -0.472 -4.843 4.631 Ascent 2.742 -0.228 1.020 -0.739 3.481 22:0×28:0 Mcfadyen and Winter [142] 3 (—, —) Descent 0.569 -3.621 -1.326 -5.485 6.054 Ascent 1.044 -0.223 0.447 -0.265 1.309 15:0×26:0 Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) Descent 0.037 -0.248 -0.558 -2.077 2.114 I: ﬁrst peak knee generation power; J: ﬁrst peak knee absorption power; K: second peak knee generation power; L: second peak knee absorption power. 100 A 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% sit-to-stand completion) (a) (b) 150 I –150 –300 –60 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Time (% sit-to-stand completion) Time (% sit-to-stand completion) (c) (d) Figure 5: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for sit-to-stand. (a) Sketch map of sit-to-stand cycle [28]. (b) Knee angle-time curve ((A) peak knee ﬂexion angle and (B) peak knee extension angle). (c) Knee moment- time curve ((E) peak knee extension moment and (F) peak knee ﬂexion moment). (d) knee power-time curve ((I) peak knee generation power) [37, 124]. that the knee quasistiﬀness was around 1.07 Nm/deg in the and 0.04 Nm/deg in the swing phase of stair ascent and stair swing phase. For running, Elliott et al. [35, 36] found that descent, respectively. For sit-to-stand, Wu et al. [37] reported the knee quasistiﬀness was around 0.38 Nm/deg in the swing that the knee quasistiﬀness was around 1.1 Nm/deg. phase and 6.6 Nm/deg in the stand phase. For stair climbing, Riener et al. [24] reported that the knee quasistiﬀness was 3.1.2. The Real Motion and Coronal Plane Biomechanics of around 2.37 Nm/deg and 2.42 Nm/deg in the weight accep- Knee Joint. Since the nonuniform shape of the knee articular tance phase of stair ascent and stair descent and 0.19 Nm/deg surface and the complicated physical structure of the femur Knee moment (Nm) Extension Knee power (W) Knee angle (deg) Flexion Generation Applied Bionics and Biomechanics 11 Table 10: Overview over the experimental results of knee angle for sit-to-stand. Subjects (mean height ± SD (m), ° ° ° Study A()B( ) ROM ( ) mean weight ± SD (kg)) Wu et al. [37] 1 (—, 75) 96 9 87 Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13)90 12 78 Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6±5)86 -1 87 Karavas et al. [124] 1 (1.85, 82.5) 86 5 81 Yu et al. [145] 10 (1:65 ± 0:05,46:2±0:8)82 22 60 Bowser et al. [146] 12 (1:66 ± 0:08, 74:2±19:5)83 -3 86 A: peak knee ﬂexion angle; B: peak knee extension angle. Table 11: Overview over the experimental results of knee moment for running. Subjects (mean height ± SD (m), Study E (Nm/kg) F (Nm/kg) Range (Nm/kg) mean weight ± SD (kg)) Wu et al. [37] 1 (—, 75) 2.187 0.609 1.578 Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13) 0.619 0 0.619 Yoshioka et al. [147] 1 (—, 73.8) 1.087 -0.038 1.125 Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6± 5) 1.132 -0.157 1.289 Karavas et al. [124] 1 (1.85, 82.5) 1.293 0.168 1.125 Bowser et al. [146] 12 (1:66 ± 0:08, 74:2±19:5) 0.901 0 0.901 Kamali et al. [30] 1 (1.72, 70) 1.126 0.136 0.990 Schoﬁeld et al. [148] 10 (1:77 ± 0:09, 70:5±8:7) 0.679 0.038 0.641 Robert et al. [149] 7 (1:75 ± 0:06, 66 ± 8) 1.136 -0.198 1.334 E: peak knee extension moment; F: peak knee ﬂexion moment. and tibia, the knee motion cannot be modeled as simple as a the knee extension motion [44, 45]. Blankevoort et al. [46], perfect hinge [38–40]. The real knee joint moves with a poly- Churchill et al. [47], and Hollister et al. [48] found that the centric motion, whereby the center of rotation changes dur- ﬂexion-extension and internal-external rotation cause the ing the rotation [41]. The femur and tibia can be trajectory of the knee center seem to be a spiral curve. approximated as a bielliptical structure, so the tibia rolls on In the coronal plane, the knee adduction moment and the loads of knee medial and lateral compartments are key the femur resulting in anterior-posterior (A-P) translation during the ﬂexion-extension motion [40]. When the rotation parameters of biomechanics. For the former, Gaasbeek et al. angle is less than 20 deg, there would be a small A-P transla- [49], Russell [50], and Briggs et al. [51] found that the maxi- tion. Thus, the movement of a real knee joint can be approx- mum adduction moment is about 0.31, 0.36, and imated as pure rolling around the ﬁxed center. But when the 0.26 Nm/(kg⋅m) in walking, respectively. Ferber et al. [52], rotation angle is more than 20 deg, the A-P translation begins Sinclair [53], and Gehring et al. [54] reported that the maxi- to increase, the amplitude of which can exceed 19 mm. Thus, mum adduction moment is about 0.52, 0.53, and the knee motion can be approximated as a gradual transition 0.58 Nm/(kg⋅m) in running, respectively. Law [26] and Mus- selman [27] represented that the maximum adduction from pure rolling, the coupled motion of rolling, and sliding to pure sliding [38, 40, 42]. Smidt [43] reported that the tra- moment is about 0.44 and 0.34 Nm/kg in stair climbing, jectory of the center of knee seems to be a J-shaped curve in respectively. Trepczynski et al. [55] reported that the maxi- the sagittal plane. mum adduction moment is about 0.45 Nm/kg in sit-to- In addition to the motion in the sagittal plane, the knee stand. For the latter, Russell [50] found that the normal knee joint always had a little varus, in other words, the medial joint also has internal-external rotation in the horizontal plane [44]. During the last 10-15 deg before complete exten- compartment bears more load than the lateral compartment. sion, the medial femoral condyle is internally rotated and the Specogna et al. [56] reported that the weight-bearing line tibia is externally rotated. At the same time, the lateral menis- (WBL) was diﬀerent in each phase of the gait. Cao [57] cus is anteriorly translated and the medial meniscus is poste- reported that the medial compartment bears 60-80% of the load. Pagani et al. [58] found that about 70% joint force pass riorly translated. Because of the larger contact surface of the medial tibiofemoral joint, the length of the medial femoral through the medial compartment to the ground. condyle is longer than that of the lateral, and because of the limitations of cruciate-collateral ligaments and quadriceps 3.2. Biomechanical Properties of Diseased Knee Joint. Accord- femoris on knee motion, the knee joint is self-locking as an ing to the pathogeny, the knee disorders can be mainly divided into musculoskeletal and neurological disorders. eccentric wheel to maintain the stability of the joint during Heel strike 12 Applied Bionics and Biomechanics 120 120 Stance Stance 0 0 Swing Swing Heel strike –60 –60 0 20 40 60 80 100 0 20406080 100 Knee angle (deg) Knee angle (deg) Flexion Flexion (a) (b) 120 120 Descent 60 60 Ascent 0 0 Sit Stand –60 –60 0 20406080 100 0 20406080 100 Knee angle (deg) Knee angle (deg) Flexion Flexion (c) (d) Figure 6: The moment-angle (stiﬀness) curves of the knee joint for normal walking, running, stair climbing, and sit-to-stand. (a) Normal walking [20, 34]. (b) Running [35, 36]. (c) Stair ascent and stair descent [24]. (d) Sit-to-stand [37]. For the former, the pathogeny is inside the knee joint, but the changes, enlarging bone marrow lesions, compartment carti- neural control system of these patients is normal. Knee oste- lage loss, joint space narrowing, and tibial plateau compres- oarthritis (KOA), knee ligament injury, and meniscus injury sion. [63, 68]. From the biomechanical view, these causes will change the tibiofemoral alignment and inﬂuence the load are the most common forms of these disorders and will be mainly discussed in this section. Some evidences showed that distribution, and then result in the deterioration of KOA the partial assistance from an external mechanism can allevi- [69]. Due to the medial compartment bearing about 70% of ate the symptoms [59]. For the latter, the actuator of the knee the total force, KOA is more commonly observed in the is normal, but the knee control system or more advanced medial compartment (MKOA) than the lateral compartment control system is injured. Although it is not considered a with a ratio of up to 4 times [58, 59]. knee joint disease in the medical ﬁeld, the neurological disor- Medical radiological assessment, kinematics analysis, ders can inﬂuence the knee movement biomechanics. Spinal kinetics analysis, and knee muscle analysis are the common cord injury (SCI), stroke, and cerebral palsy (CP) are the biomechanical methods for KOA, as shown in Table 12. In most common forms of these disorders and will be mainly the medical radiological assessment aspect, the hip-knee- discussed in this section. Some researchers pointed out that ankle angle (HKAA) on the full-0limb radiograph is regarded the partial or entire assistance from an external mechanism as the gold standard of alignment measurement, as shown in and rehabilitation training can recover the ambulatory ability Figure 7(a) [63, 69]. Chao et al. [70] reported that the normal of this patients [60, 61]. HKAA was about 178.8 deg and the angle is less than the value represented by genu varum. Russell [50] found that the 3.2.1. Knee Musculoskeletal Disorders and Its Biomechanical HKAA of normal and MKOA were about 177.7 deg and Eﬀects. KOA, one of the major health problems, aﬀects 174.2 deg, respectively. As shown in Figure 7(a), mechani- 7-17% of individuals especially for the elder, obese, and cal-lateral-distal-femoral angle (mLDFA), medial-proximal- tibial angle (MPTA), and joint-line-convergence angle previous limb injury people [62–65]. Nearly 46% of adults will develop painful KOA in at least one knee joint over their (JLCA) are also commonly used as the measurement param- lifetime [66]. By 2020, the KOA is predicted to become the eters [68]. The normal values of these angles are 85-90 deg, fourth leading cause of disability globally [67]. The etiology 85-90 deg, and 0-2 deg, respectively. The mLDFA greater than and progression of KOA are multifactorial, which includes 90 deg, MPTA less than 85 deg, or JLCA greater than 2 deg represent genu varum [71]. The mechanical axis deviation the increasing tibiofemoral force, the femoral shaft curvature Knee moment (Nm) Knee moment (Nm) Extension Extension Knee moment (Nm) Knee moment (Nm) Extension Extension Applied Bionics and Biomechanics 13 Table 12: Overview over the biomechanical eﬀects of KOA. Study Analysis Eﬀects Chao et al. [70] Medical radiology HKAA: ~178.8 deg for normal knee; <178 deg for MKOA patients mLDFA: 85-90 deg for normal knee; >90 deg for MKOA patients MPTA: 85-90 deg for normal knee; <85 deg for MKOA patients Paley [71] Medical radiology JLCA: 0-2 deg for normal knee; >2 deg for MKOA patients MAD: ~8 mm for normal knee; >8 mm for MKOA patients HKAA: ~177.7 deg for normal knee; ~174.2 deg for MKOA patients WBL ratio: ~41.4% for normal knee; ~24.2% for MKOA patients Medial joint apace: ~4.5 mm for normal knee; ~2.8 mm for Medical radiology MKOA patients Lateral joint apace: ~5.5 mm for normal knee; ~7.9 mm for Russell [50] MKOA patients Kinematics A lower knee ﬂexion angle for MKOA patients Kinetics A higher knee adduction moment for MKOA patients Muscles A lower quadriceps strength for MKOA patients A longer gait time, a smaller stride length and ROM, a greater knee Zhu et al. [72] Kinematics ﬂexion angle at heel strike, and an unobvious ﬂuctuation of knee ﬂexion angle in stand phase of walking for MKOA patients A slower walking speed, a shorter step length, a longer stance, and Kinematics double support time, and smaller cadence, stride length, and knee ROM for MKOA patients Alzahrani [73] The medial and lateral muscle cocontraction was increased for KOA Muscles patients Astephen et al. [74] Kinetics A greater knee adduction moment in mid-stance for MKOA patients A greater peak adduction moment during stair climbing for MKOA Guo et al. [75] Kinetics patients Rudolph et al. [76] and Schmitt A smaller peak knee ﬂexion moment during early and late stance Kinetics and Rudolph [77] phases for MKOA patients A 4-6 deg increase in varus alignment could increase around 70-90% Fitzgerald [78] Kinetics medial compartment load during single limb bearing Genu varum exceeding 5 deg was associated with greater functional Kinetics deterioration over 18 months than the value of 5 deg or less Lim et al. [79] No signiﬁcant relationship between the varus malalignment and the Muscles EMG ratio of VM and VL A 20% increase in the peak adduction moment could increase the KOA Kemp et al. [80] Kinetics progression risk Slemenda et al. [81], Hurley et al. Muscles A smaller quadriceps strength and muscle activation for KOA patients [82], and Oreilly et al. [83] The medial and lateral muscle cocontraction was increased for KOA Hubley-Kozey et al. [84] Muscles patients (MAD) is another measurement method. The normal MAD Zhu et al. [72] found that the KOA patients presented a longer is about 8 mm in the medial, and the value greater than the gait time, a smaller stride length and ROM, a greater knee ﬂexion angle at heel strike, and an unobvious ﬂuctuation of normal MAD represents genu varum [71]. Besides, the WBL ratio and medial or lateral joint space also used to characterize knee ﬂexion angle in the stand phase of walking. Alzahrani the KOA. Russell [50] pointed out that the WBL ratio, medial [73] indicated that the MKOA patients presented slower joint space, and lateral joint space were about 41.4%, 4.5 mm, walking speeds, shorter step lengths, longer stance and double and 5.5 mm for normal individuals and 24.2%, 2.8 mm and support time, and smaller cadence, stride length, and knee 7.9 mm for MKOA, respectively. In the knee kinematics ROM. In the knee kinetics aspect, Russell [50] described that aspect, Russell [50] reported that the knee ﬂexion pattern the knee adduction moment pattern was similar, but the mag- was similar, but the magnitude was lower for MKOA patients nitude was higher for MKOA patients compared to that for compared to that for normal subjects, as shown in Figure 7(b). normal subjects in walking, as shown in Figure 7(c). 14 Applied Bionics and Biomechanics 60 0.4 0.3 0.2 mLDFA HKAA 20 0.1 MPTA 0.0 020 40 60 80 100 0 20 40 60 80 100 MAD Time (% stance) Time (% stance) Health Health KOA KOA (a) (b) (c) Figure 7: The knee alignment measurement methods and the eﬀect of KOA on ﬂexion angle and adduction moment. (a) Sketch map of HKAA, mLDFA, MPTA, and MAD [61]. (b) Knee ﬂexion angles of health and KOA individuals [48]. (c) Knee adduction moments of health and KOA subjects [48]. Astephen et al. [74] observed that the knee adduction injuries to the ACL [89]. So, ACL injury will be mainly dis- moment in MKOA patients was greater than that in the nor- cussed in this section. mal in mid-stance. Guo et al. [75] found that the MKOA The biomechanical eﬀects of ACL were shown in patients possessed a greater peak adduction moment during Table 13. In the knee kinematics aspect, Zhao et al. [90] stair climbing. Rudolph et al. [76] and Schmitt and Rudolph reported that the knee ROM was lower for ACL-injured [77] pointed out that the peak knee ﬂexion moment in KOA patients in stair climbing. Slater et al. [91] pointed out that patients was smaller than that in the normal during early the peak knee ﬂexion angle was smaller and the peak knee adduction angle was greater for the ACL injury patients in and late stance phases. Fitzgerald et al. [78] reported that a 4-6 deg increase in varus alignment could increase around walking. Cronstrom et al. [92] represented that the knee 70-90% medial compartment load during single limb bear- adduction degree during weight-bearing activities for ACL- ing. Lim et al. [79] indicated that genu varum exceeding injured patients was greater in walking. Gao and Zheng 5 deg at baseline was associated with greater functional dete- [93] indicated that the ACL-injured patients had slower speed and smaller stride length during walking. In the knee rioration over 18 months than the value of 5 deg or less. Kemp et al. [80] observed that a 20% increase in the peak kinetics aspect, Alexander and Schwameder [94] observed a adduction moment could increase the KOA progression risk. 430% and 475% increase in the patella-femur contact force In the knee muscle aspect, Slemenda et al. [81], Hurley et al. for ACL-injured patients during upslope and downslope, [82], and Oreilly et al. [83] found that the KOA patients had respectively. Goerger et al. [95] found that the peak knee adduction moment during weight-bearing activities was smaller quadriceps strength and muscle activation. Lim et al. [79] indicated that there was no signiﬁcant relationship greater in patients after ACL than before injury. Slater et al. between the varus malalignment and the EMG ratio of [91] reported that a smaller peak external knee ﬂexion and VM and VL. Russell [50] reported that the medial muscle adduction moment can be found in the ACL-injured patients (VM-ST and VM-MG) and lateral muscle (VL-BF and during walking. Thomas and Palmieri-Smith [96] illustrated no diﬀerence in the external knee adduction moment among VL-LG) cocontraction indices were not signiﬁcantly diﬀerent between MKOA patients and normal person, but the quadri- individuals with ACL injury and those who are healthy. Nor- ceps strength was signiﬁcantly lower for MKOA patients. cross et al. [85] demonstrated that the ACL-injured patients Alzahrani [73] and Hubley-Kozey et al. [84] represented that had a greater knee energy adsorption during landing. the medial and lateral muscle cocontraction was increased Meniscus injury, as a sport-induced injury, is com- mon among athletes and general population [86, 89]. for the KOA patients. Knee ligament injury is a common and serious disease in The meniscus-injured patients are often coupled with trau- sport injuries and can signiﬁcantly change the biomechanics. matic ACL injury and can increase the stress and reduce According to where the injury hits, the knee ligament injury the stability of the knee joint during extension and ﬂexion can be divided into the ACL, PCL, TCL, FCL, and PL motions [89]. Many studies described that the secondary diseases, e.g., cartilage wear and KOA, can occur if not injuries. Many researchers pointed out that the secondary injuries, e.g., cartilage injury, meniscus injury, and KOA, treated in time [87, 88, 97]. According to the injured degree, can occur if not treated in time. And the ligament recon- diﬀerent treatments including conservative treatment, menis- struction, as a recognized eﬀective treatment, can dramati- cus suture, and meniscectomy, can be selected. cally recover the knee biomechanics [85–88]. In the ﬁve To our knowledge, there are rare research that study the biomechanical eﬀects of meniscus injury, as shown in types of injures, nearly half of ligament injuries are isolated Knee ﬂexion angle (deg) Knee adduction moment (Nm/kg·m) Applied Bionics and Biomechanics 15 Table 13: Overview over the biomechanical eﬀects of ACL and meniscus injury. Study Knee disorders Analysis Eﬀects Zhao et al. [90] ACL Kinematics A lower knee ROM during stair climbing for ACL-injured patients A greater knee adduction angle during weight-bearing activities for Gronstrom et al. [92] ACL Kinematics ACL-injured patients A slower speed and smaller stride length during walking for Gao and Zheng[93] ACL Kinematics ACL-injured patients A 430% and 475% increase in the patella-femur contact force during Alexander and Schwameder[94] ACL Kinetics upslope and downslope, respectively, for ACL-injured patients. A greater peak knee adduction moment during weight-bearing Goerger et al. [95] ACL Kinetics activities for ACL-injured patients A smaller peak knee ﬂexion angle and a greater peak knee adduction Kinematics angle during walking for ACL-injured patients Slater et al. [91] ACL Kinetics A smaller peak E-KFM and E-KAM for ACL-injured patients No diﬀerence in the E-KAM among individuals with ACL injury and Thomas et al. [96] ACL Kinetics those who are healthy Norcross et al. [85] ACL Kinetics A greater knee energy adsorption for ACL-injured patients A smaller walking speed and knee ROM and a larger cadence, step Magyar et al. [87] Meniscus injury Kinematics length, duration of support, and double support phase for meniscus injured patients A larger minimum ﬂexion angle and a smaller maximum Kinematics internal-external rotation angle for meniscus-injured patients Zhou [86] Meniscus injury A larger knee pressure and a smaller knee stressed area for Kinetics meniscus-injured patients Table 13. Magyar et al. [87] represented that the walking walking for several hours per day [98, 99, 102, 103]. The bio- speed and knee ROM of meniscus-injured patients were sig- mechanical eﬀects of SCI were shown in Table 14. Barbeau niﬁcantly smaller, and the cadence, step length, duration of et al. [104] pointed out that the knee ROM and peak knee- support, and double support phase of meniscus-injured swing-ﬂexion angle were lower, and peak knee moment was patients were remarkably larger in walking. Zhou [86] indi- larger for SCI patients in walking. Desrosiers et al. [105] found that the knee power was lower for SCI patients in cated that the maximum ﬂexion angle and maximum abduction-adduction angle between meniscus injury patients uphill and downhill walking. Pepin et al. [106] indicated that and healthy subjects have no apparent diﬀerence. The the SCI patients presented a longer ﬂexed knee at good con- meniscus-injured patients had a larger minimum ﬂexion tact and maintain the longer ﬂexion throughout the stance angle and a smaller maximum internal-external rotation phase of walking. angles in walking. And the knee stressed area was smaller Stroke, a common cerebrovascular disease, has a high and the knee pressure was larger for the meniscus-injured mortality and disability rate [107, 108]. There are about 7.0 patients in walking. million stroke survivals in China and 6.6 million in the United States [109, 110]. Stroke is known as the cause of paralysis, loss of motor function, paresis-weakness of muscle, 3.2.2. Knee Neurological Disorders and Its Biomechanical plegia-complete loss of muscle action, and muscle atrophy Eﬀects. SCI, one of the main causes of mobility disorders, [34, 108, 109]. Impaired walking and sit-stand transition aﬀects around 0.25-0.5 million people every year around are the main reason that poststroke patients cannot live inde- the world especially the young [98]. Approximately 43% of pendently [107, 108]. And about 30% of poststroke patients SCI patients turn out to have paraplegia and the number is have diﬃculty in ambulation without assistance [109]. Some increasing year by year [99]. The SCI patients are at an evidences showed that 70% of poststroke patients can recover increasing risk of many secondary medical complications, their walking capabilities by rehabilitation [108, 111]. The including muscle atrophy, pressure ulcer, bone density biomechanical eﬀects of stroke were shown in Table 14. reduction, and osteoporosis [100, 101]. Standing and walk- Sridar et al. [109] indicated that the kinematic and kinetic ing, as the most prevalent desires of these patients, can stim- performance of the poststroke patients will degrade, such as ulate blood circulation, ease muscle spasm, and increase the reduced walking speed, quadriceps muscle moment, and bone mineral density [98, 102]. Some evidences showed that quadriceps muscle power. Chen et al. [112] revealed that the SCI patients can reduce the secondary medical complica- the poststroke patients had lower knee ﬂexion in the swing tions risk and recover motion capabilities by standing or phase of walking. Stanhope et al. [113] found that the 16 Applied Bionics and Biomechanics Table 14: Overview over the biomechanical eﬀects of SCI, stroke, and CP. Study Knee disorders Analysis Eﬀects Kinematics A lower knee ROM and peak knee-swing-ﬂexion angle for SCI patients Barbeau et al. [102] SCI Kinetics A larger peak knee moment for SCI patients A lower knee power during uphill and downhill walking for SCI Desrosiers et al. [103] SCI Kinetics patients A longer knee ﬂexion at good contact and maintain the longer ﬂexion Pepin et al. [104] SCI Kinematics throughout the stance phase of walking for SCI patients. Kinematics A lower walking speed for stroke patients Sridar et al. [109] Stroke Muscles A lower quadriceps muscle moment and power for stroke patients A lower knee ﬂexion in the swing phase of walking for poststroke Chen et al. [112] Stroke Kinematics patients Post-stroke patients can compensate their poor knee ﬂexion in walking Stanhope et al. [113] Stroke Kinematics through faster speed A greater dynamic knee joint loading for stroke patients and no Marrocco et al. [114] Stroke Kinetics signiﬁcant diﬀerence between the E-KFM/E-KAM of stroke and healthy subjects. A less energy transference in mid-stance of walking and a lower energy Novak et al. [115] Stroke Kinetics absorption in the late stance of walking for stroke patients Crouch gait (characterized by excessive knee ﬂexion in stance phase), Lerner [19] and Thapa et al. [116] CP Kinetics walking ineﬃciency, and consumes much more energy Minimum knee ﬂexion angle during the stance phase exceeding 40 deg Hicks et al. [120] CP Kinematics for CP patients poststroke patients can compensate their poor knee ﬂexion in pain, and patellar stress fractures and then result in the walking through faster speed. Marrocco et al. [114] reported severity of crouch gait [19, 118, 121]. Some evidences a greater dynamic medical knee joint loading in stroke sub- showed that the mobility function can be preserved and jects in walking. However, the external knee adduction and the complications can be reduced by limiting excessive knee ﬂexion moments in walking were not signiﬁcantly diﬀerent ﬂexion in walking [118]. between the stroke patients and healthy subjects. Novak et al. [115] observed that less energy was transferred concen- trically via knee extensor muscles of stroke patients in mid- 4. Discussion and Conclusions stance of walking. And the stroke patients presented lower energy absorption by the knee extensors in the late stance Knee disorders, including musculoskeletal and neurological of walking. disorders, have serious inﬂuences on knee biomechanics. A CP, the most common pediatric neuromotor disorder, number of researches related with the biomechanics of nor- aﬀects around 0.2-0.3% live births [19, 116]. The injury in mal and diseased knee joint have been done during the last the central nervous system of the developing fetus or infant decades. Many advances have been made to understand the is the pathogenesis of CP, which eﬀects the control of move- kinematics and kinetics of normal and diseased knee during ment, balance, and posture [116, 117]. The person with CP diﬀerent common motions. In the aspect of normal knee bio- always has a variety of characteristics including rigidity, spas- mechanics, there is no clear assessment at the current state- ticity, abnormal aerobic and anaerobic capacity, decreased of-the-art. The diﬀerence between the results of diﬀerent muscle strength and endurance, abnormal muscle tone, researches is signiﬁcant. In the aspect of diseased knee bio- deformities, and muscle weakness [19, 118, 119]. The biome- mechanics, a lower knee ﬂexion angle, walking speed, mus- chanical eﬀects of CP were shown in Table 14. Crouch gait, cles strength, and a higher knee contact pressure were characterized by excessive knee ﬂexion in stance phase, is a always observed. Understanding how pathologies aﬀect the frequent gait deviation in CP patients [19, 117, 118]. Hicks knee joint biomechanics is important for designing knee et al. [120] reported the minimum knee ﬂexion angle during assistive devices and optimizing rehabilitation exercise pro- the stance phase exceed 40 deg for the CP patients. Com- gram. However, the current understanding still has not met pared with the normal gait, crouch gait is ineﬃcient and the requirement of a designer and rehabilitative physician. consumes much more energy [19, 116]. For maintaining And it is hard to ﬁnd a research that can systematic study the excessive knee ﬂexion posture in walking, the stress of all aspects of knee biomechanics completely. Thus, deeper the knee and surrounding muscles are increasing, which understanding of the biomechanics of normal and diseased can lead to bony deformities, degenerative arthritis, joint knee joint will still be an urgent need in the future. Applied Bionics and Biomechanics 17 Some limitations of the current studies must be noted. [3] K. Shamaei, M. Cenciarini, A. A. Adams, K. N. Gregorczyk, J. M. Schiﬀman, and A. M. 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Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review

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