Lower‐limb muscle function during gait in varus mal‐aligned osteoarthritis patients

This study quantified the contributions by muscular, gravitational and inertial forces to the ground reaction force (GRF) and external knee adduction moment (EKAM) for knee osteoarthritis (OA) patients and controls walking at similar speeds. Gait data for 39 varus mal‐aligned medial knee OA patients and 15 controls were input into musculoskeletal models to calculate the contributions of individual muscles and gravity to the fore‐aft (progression), vertical (support), and mediolateral (balance) GRF, and the EKAM. The temporal patterns of contributions to GRF and EKAM were similar between the groups. Magnitude differences in GRF contributions were small but some reached significance. Peak GRF contributions were lower in patients except hamstrings in early‐stance progression (p < 0.001) and gastrocnemius in late‐stance progression (p < 0.001). Both EKAM peaks were higher in patients, due mainly to greater adduction contribution from gravity (p < 0.001) at the first peak, and lower abduction contributions from soleus (p < 0.001) and gastrocnemius (p < 0.001) at the second peak. Gluteus medius contributed most to EKAM in both groups, but was higher in patients during mid‐stance only (p < 0.001). Differences in GRF contributions were attributed to altered quadriceps‐hamstrings action as well as compensatory adaptation of the ankle plantarflexors to reduced gluteus medius action. The large effect of varus mal‐alignment on the frontal‐plane moment arms of the gravity, soleus, and gastrocnemius GRF contributions about the knee explained greater patient EKAM. Our results shed further light on how the EKAM contributes to altered knee‐joint loads in OA and why some interventions may affect different portions of the EKAM waveform. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2157–2166, 2018.

     

Evidence and mechanism by which upper partial fibulectomy improves knee biomechanics and decreases knee pain of osteoarthritis

To investigate the change in short‐term clinical outcomes and biomechanical properties of the knee in response to upper partial fibulectomy and to probe into the biomechanical mechanism underlying the clinical benefits of upper partial fibulectomy for medial compartment knee osteoarthritis (KOA). A total of 29 patients with medial compartment KOA underwent upper partial fibulectomy. Visual analog scale (VAS) pain, the hospital for special surgery knee score (HSS), hip‐knee‐ankle (HKA) angle (measured in the frontal plane), and flexion/extension range of motion of the knee were assessed before and up to 6 months after surgery. Patients and 20 healthy controls were evaluated by 3D gait analysis and dynamic lower limb musculoskeletal analysis. Both VAS pain and HSS score were significantly improved (p < 0.001) one day after surgery and steadily improved during the subsequent 6 months. HKA angle improved (p = 0.025) immediately and remained stable by 3 months after surgery. The decreased overall peak KAM (decreased by 11.1%) and increased HKA angle (increased by 1.80 degrees from a more varus to more neutral alignment) of affected and operated side by 6 months after surgery were observed. Muscle activity of biceps femoris caput longum of affected and operated side increased immediately and was equivalent to healthy controls by 6 months after surgery (p = 0.007). This pilot study provides biomechanical evidence of benefit from partial upper fibulectomy and indicates a plausible rationale for the improvement in clinical symptoms. Long‐term clinical outcomes and precise biomechanical mechanism of partial upper fibulectomy should be further investigated. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2099–2108, 2018.

     

Effect of center of pressure modulation on knee adduction moment in medial compartment knee osteoarthritis

The knee adduction moment (KAM) provides a major contribution to the elevated load in the medial compartment of the knee. An abnormally high KAM has been linked with the progression of knee osteoarthritis (OA). Footwear‐generated biomechanical manipulations reduce the magnitude of this moment by conveying a more laterally shifted trajectory of the foot's center of pressure (COP), reducing the distance between the ground reaction force and the center of the knee joint, thus lowering the magnitude of the torque. We sought to examine the outcome of a COP shift in a cohort of female patients suffering from medial knee OA. Twenty‐two female patients suffering from medial compartment knee OA underwent successive gait analysis testing and direct pedobarographic examination of the COP trajectory with a foot‐worn biomechanical device allowing controlled manipulation of the COP. Modulation of the COP coronal trajectory from medial to lateral offset resulted in a significant reduction of the KAM. This trend was demonstrated in subjects with mild‐to‐moderate OA and in patients suffering from severe stages of the disease. Our results indicate that controlled manipulation of knee coronal kinetics in individuals suffering from medial knee OA can be facilitated by customized COP modification. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1668–1674, 2011     

Effects of lateral‐offset sole shoes on knee adduction moment in women with medial compartment knee osteoarthritis

This study aimed to determine the impact of wearing a lateral‐offset sole shoe (LOSS) on knee adduction moment (KAM) in patients with medial knee osteoarthritis (OA). From December 2012 to November 2016, patients with medial knee OA were recruited. Ninety‐three knees (50 left, 43 right) of 93 female patients were analyzed. The first peak KAMs were measured with patients (i) walking barefoot; (ii) walking in conventional shoes; and (iii) walking in LOSSs. The patients had grade 1 (n = 19), grade 2 (n = 49), grade 3 (n = 20), and grade 4 (n = 5) knee OA. First peak KAMs differed significantly in all three conditions (p = 0.031). In the post hoc analysis, first peak KAMs were significantly lower during LOSS walking than during conventional shoe walking (p = 0.001), but there were no differences in peak KAMs between barefoot and LOSS walking (p = 0.784). In the subgroup analysis, patients with grades 2 and 3 OA showed significantly lower first peak KAMs during LOSS walking than during conventional shoe walking (p = 0.029 and p = 0.011, respectively). Both the peak eversion ankle angle and moment of barefoot walking showed a significant increase compared with LOSS and conventional shoe walking, while there was no significant difference between LOSS and conventional shoe walking (p = 0.612 and p = 0.197, respectively). Our results suggest that LOSS wearing caused significant KAM reductions compared with conventional shoe wearing. Since LOSS wearing does not cause changes in the peak eversion ankle angle and moment during the load response, it may be an effective method to reduce the KAM in women with knee OA. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1694–1700, 2018.

     

Effects of active feedback gait retraining to produce a medial weight transfer at the foot in subjects with symptomatic medial knee osteoarthritis

This study aimed to determine if active feedback gait retraining to produce a medial weight transfer at the foot significantly reduces the knee adduction moment in subjects with medial compartment knee osteoarthritis. Secondarily, changes in peak knee flexion moment, frontal plane knee and ankle kinematics, and center of pressure were investigated. Ten individuals with medial compartment knee osteoarthritis (9 males; age: 65.3 ± 9.8 years; BMI: 27.8 ± 3.0 kg/m²) were tested at self‐selected normal and fast speeds in two conditions: Intervention, with an active feedback device attached to the shoe of their more affected leg, and control, with the device de‐activated. Kinematics and kinetics were assessed using a motion capture system and force plate. The first peak, second peak, and impulse of the knee adduction moment were significantly reduced by 6.0%, 13.9%, and 9.2%, respectively, at normal speed, with reductions of 10.7% and 8.6% in first peak and impulse at fast speed, respectively, with the active feedback system, with no significant effect on the peak knee flexion moment. Significant reductions in peak varus knee angle and medialized center of pressure in the first half of stance were observed, with reductions in peak varus knee angle associated with reductions in the knee adduction moment. This study demonstrated that active feedback to produce a medial weight‐bearing shift at the foot reduces the peaks and impulse of the knee adduction moment in patients with medial compartment knee osteoarthritis. Future research should determine the long‐term effect of the active feedback intervention on joint loading, pain, and function. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2251–2259, 2017.

     

Sex differences in knee joint loading: Cross‐sectional study in geriatric population

This study investigated sex differences in knee biomechanics and investigated determinants for difference in a geriatric population. Age‐matched healthy volunteers (42 males and 42 females, average age 65 years) without knee OA were included in the study. Subjects underwent physical examination on their knee and standing full‐limb radiography for anthropometric measurements. Linear, kinetic, and kinematic parameters were compared using a three‐dimensional, 12‐camera motion capture system. Gait parameters were evaluated and determinants for sex difference were evaluated with multiple regression analysis. Females had a higher peak knee adduction moment (KAM) during gait (p = 0.004). Females had relatively wider pelvis and narrower step width (both p < 0.001). However, coronal knee alignment was not significantly different between the sexes. Multiple regression analysis revealed that coronal alignment (b = 0.014, p < 0.001), step width (b = −0.010, p = 0.011), and pelvic width/height ratio (b = 1.703, p = 0.046) were significant determinants of peak KAM. Because coronal alignment was not different between the sexes, narrow step width and high pelvic width/height ratio of female were the main contributors to higher peak KAM in females. Sex differences in knee biomechanics were present in the geriatric population. Increased mechanical loading on the female knee, which was associated with narrow step width and wide pelvis, may play an important role in future development and progression of OA. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1283–1289, 2017.

     

The relationship between reductions in knee loading and immediate pain response whilst wearing lateral wedged insoles in knee osteoarthritis

Studies of lateral wedge insoles (LWIs) in medial knee osteoarthritis (OA) have shown reductions in the average external knee adduction moment (EKAM) but no lessening of knee pain. Some treated patients actually experience increases in the EKAM which could explain the overall absence of pain response. We examined whether, in patients with painful medial OA, reductions in the EKAM were associated with lessening of knee pain. Each patient underwent gait analysis whilst walking in a control shoe and two LWI's. We evaluated the relationship between change in EKAM and change in knee pain using Spearman Rank Correlation coefficients and tested whether dichotomizing patients into biomechanical responders (decreased EKAM) and non‐responders (increased EKAM) would identify those with reductions in knee pain. In 70 patients studied, the EKAM was reduced in both LWIs versus control shoe (?5.21% and ?6.29% for typical and supported wedges, respectively). The change in EKAM using LWIs was not significantly associated with the direction of knee pain change. Further, 54% were biomechanical responders, but these persons did not have more knee pain reduction than non‐responders. Whilst LWIs reduce EKAM, there is no clearcut relationship between change in medial load when wearing LWIs and corresponding change in knee pain. © 2014 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. J Orthop Res 32:1147–1154, 2014.

     

Unilateral hip osteoarthritis: The effect of compensation strategies and anatomic measurements on frontal plane joint loading

In order to reduce pain caused by the affected hip joint, unilateral hip osteoarthritis patients (HOAP) adopt characteristic gait patterns. However, it is unknown if the knee and hip joint loading in the non‐affected (limb_{non‐affected}) and the affected (limb_affected) limb differ from healthy controls (HC) and which gait parameters correlate with potential abnormal joint loading. Instrumented 3D‐gait analysis was performed on 18 HOAP and 18 sex, age, and height matched HC. The limb_{non‐affected} showed greater first and second peak external hip adduction moments (first HAM: +15%, p = 0.014; second HAM: +15%, p = 0.021, respectively), than seen in HC. In contrast, the second peak external knee adduction moment (KAM) in the limb_affected is reduced by about 23% and 30% compared to the limb_{non‐affected} and HC, respectively. Furthermore, our patients showed characteristic gait compensation strategies including reduced peak vertical forces (pvF), a greater foot progression angle (FPA), and reduced knee range of motion (ROM) in the limb_affected. The limb_affected was 5.6 ± 3.8 mm shorter than the limb_{non‐affected}. Results of stepwise regression analyses showed that increased first pvF explain 16% of first HAM alterations, whereas knee ROM and FPA explain 39% of second KAM alterations. We therefore expect an increased rate of progression of OA in the hip joint of the limb_{non‐affected} and suggest that the shift in the medial‐to‐lateral knee joint load distribution may impact the rate of progression of OA in the limb_affected. The level of evidence is III. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1764–1773, 2017.

     

The effect of laterally wedged shoes on the loading of the medial knee compartment‐in vivo measurements with instrumented knee implants

A conventional method to unload the medial compartment of patients with gonarthrosis and thus to achieve pain reduction is the use of laterally wedged shoes. Our aim was to measure in vivo their effect on medial compartment loads using instrumented knee implants. Medial tibio‐femoral contact forces were measured in six subjects with instrumented knee implants during walking with the following shoes: without wedge, with 5 and 10 mm wedges under the lateral sole, and with a laterally wedged insole (5 mm). Measurements were repeated with the shoes in combination with an ankle‐stabilizing orthosis. Without orthosis, peak medial forces were reduced by only 1–4% on average. With orthosis, the average reduction was 2–7%. Highest reductions were generally observed with the 10 mm wedge, followed by the 5 mm wedge, and the 5 mm insole. Individual force reductions reached up to 15%. Medial force reductions while walking with wedged shoes were generally small. Due to high inter‐individual differences, it seems that some patients might benefit from lateral wedges, whereas others might not. Further analyses of the individual kinematics will show which factors are most decisive for the reduction of medial compartment load. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1910–1915, 2011     

Immediate and short‐term effects of real‐time knee adduction moment feedback on the peak and cumulative knee load during walking

The peak external knee adduction moment (pKAM), KAM impulse, and peak knee flexion moment (pKFM) during gait are important loading variables in medial tibiofemoral osteoarthritis. We evaluated the effects of gait modification, using real‐time pKAM visual feedback, on pKAM, KAM impulse, and pKFM; and whether participants could maintain the KAM‐reducing gait after feedback removal. Eleven healthy individuals performed a series of walking trials on a split‐belt instrumented treadmill under four conditions of Baseline, Feedback, No Feedback Early, and No Feedback Late. Guided by real‐time feedback of pKAM, they modified their gait patterns to lower pKAM by 20%. Three‐dimensional joint kinematics/kinetics during each walking condition were recorded by a 12‐camera motion capture system and the instrumented treadmill. Change in each knee loading parameter from baseline across conditions was assessed using one‐way repeated‐measures analysis‐of‐variances. In the feedback limb, successful 20% reductions from baseline in pKAM and KAM impulse were achieved across all three conditions. There was a trend for concomitant pKFM increases, partially attenuating the beneficial effects of pKAM reduction. A carry‐over effect of KAM reduction in the non‐feedback limb was noted. The altered gait patterns were participant‐specific and multi‐modal; each participant reported a combination of two to three gait modification strategies used for pKAM reduction. Toe‐in and medial foot contact were the most reported strategies. The findings support the real‐time pKAM visual feedback as a tool for individualized gait modification to reduce knee load. Future studies to evaluate its effectiveness in persons with or at risk for medial knee osteoarthritis is warranted. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:397–404, 2018.     

Contributions of muscles, ligaments, and the ground-reaction force to tibiofemoral joint loading during normal gait.

The aim of this study was twofold: first, to determine which muscles and ligaments resist the adduction moment at the knee during normal walking; and second, to describe and explain the contributions of muscles, ligaments, and the ground reaction force to medial and lateral compartment loading. Muscle forces, ground reaction forces, and joint motions obtained from a dynamic optimization solution for normal walking were used as input to a three-dimensional model of the lower limb. A static equilibrium problem was solved at each instant of the gait cycle to determine tibiofemoral joint loading at the knee. Medial compartment loading was determined mainly by the orientation of the ground reaction force. Because this force vector passed medial to the knee, it applied an adduction moment about the joint during stance. In contrast, all of the force transmitted by the lateral compartment was due to muscle and ligament action. The muscles that contributed most to support and forward propulsion during normal walking (quadriceps and gastrocnemius) also contributed most to knee stability in the frontal plane. The knee ligaments, particularly those of the posterior lateral corner, provided stability to the knee at certain periods of the stance phase, when activity of the important stabilizing muscles was low.     

Verification of biomechanical factors of gait related to medial knee loading in patients 6 Months after total knee arthroplasty

BackgroundThe knee adduction moment (KAM) is considered an index for estimating the knee mechanical load, and increased KAM peak and KAM impulse are related to increased medial knee load and progression of knee joint degeneration. We aimed to verify the biomechanical factors of gait related to medial knee loading in patients 6 months after TKA.MethodsThirty-nine women who underwent TKA were enrolled. A three-dimensional gait analysis was performed 6 months postoperatively to generate data on the lower limb joint angle, moment, and power at the backward component (braking phase) and forward component (propulsion phase) peaks of the ground reaction force. Medial knee loading was evaluated using the time-integrated value of KAM during the stance period (KAM impulse). The higher the value of the KAM impulse, the higher the medial knee joint load. The relationships between the KAM impulse and the data for biomechanical factors were evaluated using partial correlation analysis with gait speed as a control factor.ResultsIn the braking phase, the KAM impulse positively correlated with the knee adduction angle (r = 0.377) and negatively correlated with the toe-out angle (r = −0.355). The KAM impulse positively correlated with the knee adduction angle (r = 0.402), the hip flexion moment (r = 0.335), and the hip adduction moment (r = 0.565) and negatively correlated with the toe-out angle (r = −0.357) in the propulsive phase.ConclusionThe KAM impulse 6 months after TKA was related to the knee adduction angle, hip flexion moment, hip adduction moment, and toe-out angle. These findings may provide fundamental data for controlling variable medial knee joint load after TKA and implementing patient management strategies to ensure implant durability.     

Contribution of tibiofemoral joint contact to net loads at the knee in gait

Inverse dynamics analysis is commonly used to estimate the net loads at a joint during human motion. Most lower‐limb models of movement represent the knee as a simple hinge joint when calculating muscle forces. This approach is limited because it neglects the contributions from tibiofemoral joint contact forces and may therefore lead to errors in estimated muscle forces. The aim of this study was to quantify the contributions of tibiofemoral joint contact loads to the net knee loads calculated from inverse dynamics for multiple subjects and multiple gait patterns. Tibiofemoral joint contact loads were measured in four subjects with instrumented implants as each subject walked at their preferred speed (normal gait) and performed prescribed gait modifications designed to treat medial knee osteoarthritis. Tibiofemoral contact loads contributed substantially to the net knee extension and knee adduction moments in normal gait with mean values of 16% and 54%, respectively. These findings suggest that knee‐contact kinematics and loads should be included in lower‐limb models of movement for more accurate determination of muscle forces. The results of this study may be used to guide the development of more realistic lower‐limb models that account for the effects of tibiofemoral joint contact at the knee. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1054–1060, 2015.     

Kinematics of meniscal‐ and ACL‐transected mouse knees during controlled tibial compressive loading captured using roentgen stereophotogrammetry

Pre‐clinical studies of post‐traumatic OA have examined the pathways that lead to disease after injury by using surgical models such as the destabilization of the medial meniscus (DMM) and anterior cruciate ligament transection (ACLT). While the morphological, molecular, and genetic pathways leading to OA have been examined extensively; the effects of these injuries on joint kinematics, and thus disease progression, have yet to be fully characterized. To this end, we sought to understand the kinematics in the DMM and ACLT joints compared to intact joints subjected to controlled tibial compressive loading. We hypothesized that the DMM and ACLT models would result in different patterns of joint instability compared to intact joints, thus explaining the different patterns of OA initiation and severity in these models. Cadaver adult C57BL/6 mice were subjected to either a DMM or ACLT in their right knee joints, while the left limbs remained as intact controls. All limbs were labeled with fiducial markers, and the rigid body kinematics of the tibia and femur were examined using roentgen stereophotogrammetry (RSA) with application of compressive loads from 0 to 9 N. DMM and intact joints demonstrated similar kinematics under compressive loading, in contrast to ACLT joints, which dislocated even before load application. These results demonstrate the importance of rigorous kinematic analysis in defining the role of joint instability in animal models of OA and suggest significant differences in DMM and ACLT joint instabilities in the context of controlled mechanical loading. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:353–360, 2017.

     

The effect of different types of insoles or shoe modifications on medial loading of the knee in persons with medial knee osteoarthritis: a randomised trial

Many conservative treatments exist for medial knee osteoarthritis (OA) which aims to reduce the external knee adduction moment (EKAM). The objective of this study was to determine the difference between different shoes and lateral wedge insoles on EKAM, knee adduction angular impulse (KAAI), external knee flexion moment, pain, and comfort when walking in individuals with medial knee OA. Seventy individuals with medial knee OA underwent three‐dimensional walking gait analysis in five conditions (barefoot, control shoe, typical wedge, supported wedge, and mobility shoe) with pain and comfort recorded concurrently. The change in EKAM, KAAI, external knee flexion moment, pain, and comfort were assessed using multiple linear regressions and pairwise comparisons. Compared with the control shoe, lateral wedge insoles and barefoot walking significantly reduced early stance EKAM and KAAI. The mobility shoe showed no effect. A significant reduction in latter stance EKAM was seen in the lateral wedge insoles compared to the other conditions, with only the barefoot condition reducing the external knee flexion moment. However, the mobility shoe showed significant immediate knee pain reduction and improved comfort scores. Different lateral wedge insoles show comparable reductions in medial knee loading and in our study, the mobility shoe did not affect medial loading. © 2015 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. J Orthop Res 33:1646–1654, 2015.     

Three-month efficacy of three knee braces in the treatment of medial knee osteoarthritis in a randomized crossover trial

Immediate biomechanical and functional effects of knee braces are often reported, however, the duration and type of knee brace treatment for knee osteoarthritis (KOA) remain unclear. The objective was to evaluate usage, comfort, pain, and knee adduction moment (KAM) of three knee braces each worn 3 months by patients. Twenty-four patients with KOA were assigned in a randomized crossover trial a valgus three-point bending system brace (V3P-brace), an unloader brace with valgus and external rotation functions (VER-brace) and a stabilizing brace used after ligament injuries (ACL-brace). Functional questionnaires and gait assessment were carried out before and after each brace wear period of 3 months. A Friedman test was applied between brace wear diary recordings. Repeated measures analyses of variance contrasted the factors brace type (ACL, V3P, and VER), time (pre and post) and wear (without and with) on comfort, pain, function, and KAM. Brace usage was similar, but the V3P-brace was slightly less worn. Discomfort was significantly lowered with the VER-brace. All knee braces relieved pain and symptoms from 10% to 40%. KAM angular impulse was reduced with the three braces, but the VER-brace obtained the lowest relative reduction of 9%. The interaction between time and wear indicated that part of the KAM reduction with brace wear was maintained post treatment. All three knee braces have great benefits for pain and function among the medial KOA population. The VER-brace offers additional advantages on daily use, comfort and KAM, which could improve compliance to brace treatment.     

A comparison of coronal plane axial femoral relationships in Asian patients with varus osteoarthritic knees and healthy knees

Standing full-length radiographs were measured to compare coronal femoral axes between 250 limbs in patients with varus osteoarthritis with 50 healthy controls. Mean distal femoral axis-mechanical axis angle was 7.3° ± 1.6°, and mean femoral bow was 3.6° ± 2.5° in patients compared to 5.5° ± 0.8° and 0.4° ± 1.2°, respectively, in controls. Femoral condylar-mechanical axis angle was significantly lower in osteoarthritic limbs (89.9° + 2.8°) as compared to controls (93.1° + 1.6°). Varus deformity correlated significantly with femoral bowing (P < .05; correlation coefficient, 0.4). Osteoarthritic limbs (18.8%) showed a distal femoral axis-mechanical axis angle more than 9°. These findings have implications in deciding the optimum valgus angle at which to perform distal femoral resection in total knee arthroplasty.     

Localization of the full‐thickness cartilage lesions in medial and lateral unicompartmental knee osteoarthritis

This study's aim was to determine the patterns of osteoarthritis (OA) in both unicompartmental medial and lateral OA of the knee. Forty patients with medial and 20 with lateral unicompartmental knee osteoarthritis were studied to determine the location of full‐thickness cartilage lesions. Intraoperatively, the distance between margins of the lesion and reference lines were measured. The femoral measurements were transposed onto lateral radiographs to determine the relationship between the lesion site and knee flexion angles. Both tibial and femoral lesions were significantly (p < 0.01) more posterior in lateral OA than medial OA. In medial OA, the lesion center was, on average, at 11° (SD 3°) of flexion, whereas in lateral OA, it was at 40° (SD 3°). The smallest medial femoral lesions were near full extension and, as they enlarged, they extended posteriorly. The smallest lateral femoral lesions extended from 20° to 60° flexion. As these lesions enlarged, they extended both anteriorly and posteriorly. There was a well‐defined relationship between the site of the lesions and their size, suggesting that they develop and progress in a predictable manner. The relationship was different for medial and lateral OA, suggesting that different mechanical factors are important in initiating the different types of OA. The lesions in medial OA occur in extension, perhaps initiated by events occurring at heel strike. The lesions in lateral OA begin at flexion angles above those occurring during the single leg stance phase of the gait cycle, so activities other than gait are likely to induce lateral OA. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1339–1346, 2009     

Effect of component mal‐rotation on knee loading in total knee arthroplasty using multi‐body dynamics modeling under a simulated walking gait

Mal‐rotation of the components in total knee arthorplasty (TKA) is a major cause of postoperative complications, with an increased propensity for implant loosening or wear leading to revision. A musculoskeletal multi‐body dynamics model was used to perform a parametric study of the effects of the rotational mal‐alignments in TKA on the knee loading under a simulated walking gait. The knee contact forces were found to be more sensitive to variations in the varus–valgus rotation of both the tibial and the femoral components and the internal–external rotation of the femoral component in TKA. The varus–valgus mal‐rotation of the tibial or femoral component and the internal–external mal‐rotation of the femoral component with a 5° variation were found to affect the peak medial contact force by 17.8–53.1%, the peak lateral contact force by 35.0–88.4% and the peak total contact force by 5.2–18.7%. Our findings support the clinical observations that a greater than 3° internal mal‐rotation of the femoral component may lead to unsatisfactory pain levels and a greater than 3° varus mal‐rotation of the tibial component may lead to medial bone collapse. These findings determined the quantitative effects of the mal‐rotation of the components in TKA on the contact load. The effect of such mal‐rotation of the components of TKA on the kinematics would be further addressed in future studies. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1287–1296, 2015.