Purpose: To test the null hypotheses that no significant differences in the net external knee adduction moment waveform captured during gait exist between neutral, toe in and toe out foot progression angle (FPA) modifications and between those with mild to moderate knee OA and asymptomatic control subjects. Method: Ten patients with mild to moderate knee OA (age 45±7 years) and 16 asymptomatic control subjects (age 54±8 years) participated. Informed consent was obtained for all participants. Three-dimensional (3D) motion and ground reaction force data were recorded during gait. Five trials of each condition,. Self-selected walking (Neutral),. Toe out walking (10o> self-selected, velocity +/− 0.1 m/s of self-selected) and. Toe in walking (10o. Results: There was a significant condition effect for FPA (Neutral=7o, Toe out=24o and Toe in=−9o) and a significant group effect for walking velocity (Asymptomatic=1.46m/s, Knee OA=1.27m/s). In both groups, a toe out FPA produced. a reduction in the overall knee adduction moment (captured by PC1),. a reduction in the late stance magnitude of the knee adduction moment magnitude (captured by PC2 and PC3) and. an increase in the early stance knee adduction moment magnitude (captured by PC2) (p< 0.05). Conclusion: The knee adduction moment is considered an indicator of medial tibio-femoral compressive loading. In this study, a toe out FPA modification during gait altered the characteristics of the knee adduction moment. A reduction in the overall magnitude, more specifically during late stance was found with the toe out gait modification. An increased initial stance peak magnitude was also found during toe out gait. This finding is novel, indicating that a greater peak medial compartment load is produced

The knee adduction moment is indicative of the degree of medial compartmental loading at the knee joint and has been related to the presence and progression of knee osteoarthritis (OA). Studies have reported differences between OA and asymptomatic groups when measuring the adduction moment at the knee; however, there have been various biomechanical models used to describe this moment. In addition, non-invasive interventions have been shown to decrease the adduction moment but only at certain portions of the gait cycle. The objective of the study was to determine if changing the biomechanical model would affect the ability to detect differences between OA and asymptomatic gait and whether these differences depended on which portion of the gait cycle was analysed. The gait of forty-four asymptomatic and forty-four moderate OA subjects was measured. The adduction moment was calculated using three different biomechanical models commonly used in the literature:. a 2D representation of the lower limb,. a 3D coordinate system based in the tibia, and. a 3D coordinate system based in both the tibia and femur. The adduction moment waveforms were compared between groups for various portions of the gait cycle for all three models. The choice of biomechanical model changed the overall magnitude and shape of the adduction moment waveform. These changes affected the ability to detect group differences using commonly reported parameters of the adduction moment. However, group separation was achieved (regardless of model) when analyzing the overall magnitude of the adduction moment across stance phase and the mid-stance portion of the gait cycle. These results demonstrate that the OA subjects are not unloading the medial compartment of the knee at full weight acceptance as well as the healthy controls. Furthermore, the OA subjects are experiencing a higher medial compartment load that is being sustained for the duration of the stance phase of the gait cycle. Group differences that are not model dependent may be important in understanding the pathomechanics of OA and evaluating interventions. These findings support the need for a better understanding of the anatomical mechanisms associated with the adduction moment

Create an optimization model of the internal structure of the knee joint to quantify the correlation between external knee adduction moment (M[add]) during gait with the medial-to-lateral ratio of compartment loading (MLR). Patients were examined the week before, and six months after, surgical knee joint realigment with a high tibial osteotomy (HTO). Thirty patients (six females, twenty-four males; age = 50.0 ± 9.4 yrs.; BMI = 30.0±2.8) with clinically diagnosed OA primarily affecting the medial compartment of the knee underwent a medial opening wedge HTO. Walking gait analysis was performed immediately pre-surgery and at six months post-surgery using optical motion analysis (eight Eagle camera EvaRT system, Motion Analysis Corp, Santa Rosa, CA, USA) and floor-mounted force plate (OR6, AMTI, Watertown, MA, USA). External joint kinetics were calculated using inverse dynamics. Kinematic and force plate data served as input for the internal knee joint model. The anatomical geometry was generic but scaled to patient height and knee alignment. Included were four ligaments (ACL, PCL, LCL, MCL), two contact surfaces (medial and lateral) and eleven muscles (quadriceps, hamstrings, gracilis, sartorius, popliteus and gatrocnemius). A loading solution was found to satisfy mechanical equilibrium and minimise the sum of squares of all structural loads. Output was the ratio of medial-to-lateral compartment compression (MLR). Paired t-tests compared M[add] pre-op versus post-op and MLR pre-op versus post-op. A Pearson R2 coefficient of determination was calculated correlating M[add] to MLR for the pre-operative condition. Peak M[add] decreased from 2.53 ± 1.32 to 1.63 ± 0.81 [%body weight*ht] (p< 0.001). The peak MLR decreased from 2.63 ± 1.08 to 1.52 ± 0.56 [unit-less] (p< 0.001). There was a moderate correlation between M[add] and MLR with the Pearson R2=0.457 (p=0.014). These results suggest that adduction moment is an acceptable proxy for quantifying the internal compressive loading in the knee. Even without considering muscle loading and possible co-contraction of antagonists, adduction moment explains nearly half of the variance in the internal loading of the knee joint compartments. However, further research is required with a larger sample size to increase confidence in this proxy measure in a clinical setting

Determine the association between net external knee adduction moment (KAM) characteristics and foot progression angle (FPA) in asymptomatic individuals and those with moderate and severe osteoarthritis through discrete variable and principal component analysis (PCA). Fifty-nine asymptomatic (age 52 ± 10 years), fifty-five with moderate knee OA (age 60 ± 9 years) and sixty-one individuals with severe knee OA (age 67 ± 8 years, tested within one week of total knee replacement surgery) participated. Three-dimensional (3D) motion (Optotrak) and ground reaction force (AMTI) data were recorded during gait. Subjects walked at a self-selected velocity. The KAM, calculated using inverse dynamics was time normalised to one complete gait cycle. FPA was calculated using stance phase kinematic gait variables. The discrete variable, peak KAM, was extracted for the interval (30–60%) of the gait cycle. PCA was used to extract the predominant waveform features (Principal Components (PC)) of which PC-Scores were computed for each original waveform. Pearson Product Moment Correlations were calculated for the FPA and both the PC-scores and peak KAM. Alpha of 0.05 used to test significance. No significant correlations were noted for the groups between peak KAM and the FPA, or for the first PC-Scores (PC1) of which captured the original KAM waveforms overall magnitude and shape. The second PC (PC2) captured the shape and magnitude during the second interval of stance (30–60%) with respect to the first. Correlations of FPA to PC2 were significant for the asymptomatic group(r=−0.40, p=0.002) and the moderate OA group (r=−0.32, p=0.017) but not for the severe group(r=−0.13, p=0.316). No relationship between FPA and peak KAM was found across the groups using discrete variable analysis despite reports of associations in asymptomatic subjects. The PCA results suggest a toe out FPA was moderately correlated to a decreased KAM during 30–60% of the gait cycle for asymptomatic and moderate OA individuals only. These individuals respond to a toe out progression angle, altering the KAM which directly affects medial knee compartment loading, where those with severe OA do not

Aims. This study aimed to analyze kinematics and kinetics of the tibiofemoral joint in healthy subjects with valgus, neutral, and varus limb alignment throughout multiple gait activities using dynamic videofluoroscopy. Methods. Five subjects with valgus, 12 with neutral, and ten with varus limb alignment were assessed during multiple complete cycles of level walking, downhill walking, and stair descent using a combination of dynamic videofluoroscopy, ground reaction force plates, and optical motion capture. Following 2D/3D registration, tibiofemoral kinematics and kinetics were compared between the three limb alignment groups. Results. No significant differences for the rotational or translational patterns between the different limb alignment groups were found for level walking, downhill walking, or stair descent. Neutral and varus aligned subjects showed a mean centre of rotation located on the medial condyle for the loaded stance phase of all three gait activities. Valgus alignment, however, resulted in a centrally located centre of rotation for level and downhill walking, but a more medial centre of rotation during stair descent. Knee adduction/abduction moments were significantly influenced by limb alignment, with an increasing knee adduction moment from valgus through neutral to varus. Conclusion. Limb alignment was not reflected in the condylar kinematics, but did significantly affect the knee adduction moment. Variations in frontal plane limb alignment seem not to be a main modulator of condylar kinematics. The presented data provide insights into the influence of anatomical parameters on tibiofemoral kinematics and kinetics towards enhancing clinical decision-making and surgical restoration of natural knee joint motion and loading. Cite this article: Bone Joint Res 2024;13(9):485–496

The peak external knee adduction moment during walking gait has been proposed to be a clinically useful measure of dynamic knee joint load in patients with knee osteoarthritis. However, there is limited information about the reliability of this measure, or its ability to detect change. The test-retest reliability and sensitivity to change of peak knee adduction moments were evaluated in thirty patients with varus gonarthrosis. Indices of relative and absolute reliability were excellent (intra-class correlation coefficient = 0.85, standard error of measurement = 0.36 % BW*Ht), and the sensitivity to change following high tibial osteotomy was high (standardized response mean = 1.2). To estimate the test-retest reliability, measurement error and sensitivity to change of the peak knee adduction moment during gait. Thirty patients (44”11 yrs, 1.7”0.09 m, 87”20 kg, twenty males, ten females) with varus gonarthrosis underwent gait analyses on two pre-operative test occasions within one week, and on a third test occasion six months after medial opening wedge high tibial osteotomy. Three-dimensional kinematic and kinetic gait data were collected during self-paced walking and used to calculate the peak knee adduction moment. An intraclass correlation coefficient of 0.85 (95%CI: 0.71, 0.93) indicated excellent relative reliability, and a standard error of measurement of 0.36 %BW*Ht (95%CI: 0.29, 0.49) indicated low measurement error. The peak knee adduction moment after surgery (1.66”0.72 %BW*Ht) was significantly (p< 0.001) lower than before surgery (2.58”0.72 %BW*Ht). A standardized response mean of 1.2 (95%CI: 0.77, 1.6) indicated the size of this change was large. Based on 95% confidence levels, these results suggest the error in an individual’s peak knee adduction moment at one point in time is 0.70 % BW*Ht, the minimal detectable change in an individual’s peak adduction moment is 1.0 %BW*Ht, and it is sensitive to change following treatment. The peak knee adduction moment during gait has appropriate reliability for use in studies evaluating the effect of treatments intended to decrease the load on the knee. When considering measurement error, the knee adduction moment is also appropriate for clinical use in evaluating change in individual patients. Funding: CIHR, Arthrex Inc

Total knee arthroplasty (TKA) has been shown to improve knee joint function during gait post-operatively. However, there is considerable patient to patient variability, with most gait mechanics metrics not reaching asymptomatic levels. To understand how to target functional improvements with TKA, it is important to identify an optimal set of functional metrics that remain deficient post-TKA. The purpose of this study was to identify which combination of knee joint kinematics and kinetics during gait best discriminate pre-operative gait from postoperative gait, as well as post-operative from asymptomatic. Seventy-three patients scheduled to receive a TKA for severe knee osteoarthritis underwent 3D gait analysis 1 week before and 1 year after surgery. Sixty asymptomatic individuals also underwent analysis. Eleven discrete gait parameters were extracted from the gait kinematic and kinetic waveforms, as previously defined (Astephen et al., J Orthop Res., 2008). Stepwise linear discriminant analyses were used to determine the sets of parameters that optimally separated pre-operative from post-operative gait, and post-operative from asymptomatic gait. Cross-validation was used to quantify group classification error. Knee flexion angle range, knee adduction moment first peak, and gait velocity were included in the optimal discriminant function between the pre- and post-operative groups (P<0.05), with relatively equal standardised canonical coefficients (0.567, −0.501, 0.565 respectively), and a total classification rate of 74%. A number of metrics were included in the discriminant function to optimally separate post-operative and asymptomatic gait function, including the knee flexion angle range, peak stance knee flexion angle, minimum late stance knee extension moment, minimum mid-stance knee adduction moment, and peak knee internal rotation moment (P<0.05). The mid-stance knee adduction moment had the largest standardised canonical coefficients in the function, and 89.5% of cases were correctly classified. Separation of pre and post-operative gait patterns included only three parameters, suggesting that current standard of care TKA significantly improves only walking velocity, knee flexion angle range, and the peak value of the knee adduction moment. A number of gait metrics, which were included in the discriminant function between post-operative and asymptomatic gait, could benefit from further improvement either through rehabilitation or design. With almost 90% classification, separation of post-operative gait function from asymptomatic levels is significant. The consolidation of knee joint function during gait into single, discrete discriminant scores allows for an efficient summary representation of patient-specific (or implant-specific) improvement in gait function from TKA surgery

Summary. This study shows a significant reduction in knee adduction moment in patients with medial compartment osteoarthritis, in both the symptomatic and asymptomatic knees. Long-term follow-up studies are required to confirm the effect of treating the asymptomatic side on disease progression. Background. The knee is the commonest joint to be affected by osteoarthritis, with the medial compartment commonly affected. Knee osteoarthritis is commonly bilateral, yet symptoms may initially present unilaterally. Higher knee adduction moment has been associated with the development and progression of medial compartment knee osteoarthritis. The aim of this study was to assess the effect of lateral wedge insoles on the asymptomatic knee of patients with unilateral symptoms of medial compartment knee osteoarthritis. Methods. Twenty patients were assessed using a 3D optoelectronic tracking system, with 16 infrared camera, passive markers and four force platforms. Three different insoles were tested; a standard control shoe, the Boston lateral wedge insole (inclined at 5° throughout the full length of the insole) and the Salford insole (inclined at 5° throughout the full length of the insole, with medial arch support). A minimum of 5 trials per each insole were used. Kinetic and kinematic data were collected and processed using Qualysis Track Manager ® and Visual 3D™. Results. There was a significant reduction in knee adduction moment for both the Salford and Boston insoles as compared to the control shoe. This was 9.5–14.2% for the asymptomatic side, and 5.8–10.7% for the symptomatic side for the Salford and Boston insoles respectively. Although the reduction was larger on the asymptomatic side, this was not statistically significant. Patients reported significant reduction in pain with both Salford and Boston insoles as compared to the control shoe, and found the Salford insole to be the most comfortable. Stride length and walking speed was significantly higher with the Salford insole. Conclusions. This study confirms the effect of lateral wedge insoles on reducing knee adduction moment in patients with medial compartment osteoarthritis, in both the symptomatic and asymptomatic knees. Long-term follow-up studies are required to confirm the effect of treating the asymptomatic side on disease progression

Background. The knee is the commonest joint to be affected by osteoarthritis, with the medial compartment commonly affected. Knee osteoarthritis is commonly bilateral, yet symptoms may initially present unilaterally. Higher knee adduction moment has been associated with the development and progression of medial compartment knee osteoarthritis. Objectives. To assess the effect of lateral wedge insoles on the asymptomatic knee of patients with unilateral symptoms of medial compartment knee osteoarthritis. Methods. Twenty patients were assessed using a 3D optoelectronic tracking system, with 16 infrared camera, passive markers and four force platforms. Three different insoles were tested; a standard control shoe, the Boston lateral wedge insole (inclined at 5° throughout the full length of the insole) and the Salford insole (inclined at 5° throughout the full length of the insole, with medial arch support). A minimum of 5 trials per each insole were used. Kinetic and kinematic data were collected and processed using Qualysis Track Manager ® and Visual 3D™. Results. There was a significant reduction in knee adduction moment for both the Salford and Boston insoles as compared to the control shoe. This was 9.5–14.2% for the asymptomatic side, and 5.8–10.7% for the symptomatic side for the Salford and Boston insoles respectively. Although the reduction was larger on the asymptomatic side, this was not statistically significant. Patients reported significant reduction in pain with both Salford and Boston insoles as compared to the control shoe, and found the Salford insole to be the most comfortable. Stride length and walking speed was significantly higher with the Salford insole. Conclusions. This study confirms the effect of lateral wedge insoles on reducing knee adduction moment in patients with medial compartment osteoarthritis, in both the symptomatic and asymptomatic knees. Long-term follow-up studies are required to confirm the effect of treating the asymptomatic side on disease progression

Purpose: Hip muscle weakness may result in impaired frontal plane pelvic control during gait, leading to greater medial compartment loading, as measured by the knee adduction moment, in persons with knee osteoarthritis (OA). The purpose of this study was to evaluate the influence of an 8-week home-based strengthening program for the hip abductor muscles on hip muscle strength and the external knee adduction moment during gait in individuals with medial knee OA compared to an asymptomatic control group. Secondary objectives were to determine if hip abductor strengthening exercises would improve physical function and knee symptoms in this sample of people with knee OA. Method: Forty participants with knee OA were age and gender-matched with an asymptomatic control group. Three-dimensional gait analysis was performed to obtain peak knee adduction moments in the first 50% of stance phase. Isokinetic concentric strength of the hip abductor muscles was measured using a Biodex Isokinetic Dynamometer. Functional performance was evaluated using the Five-Times-Sit-to-Stand test. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) provided an assessment of knee pain. Following initial testing, participants with knee OA were instructed in a home program of hip abductor strengthening exercises. All participants were re-evaluated after 8 weeks. Results: There was no significant difference in isokinetic hip abductor muscle strength between groups at baseline or at follow-up. An improvement in hip abductor strength occurred in the OA group following the intervention (p = 0.036). The OA group had higher peak knee adduction moments than the control group (p = 0.006), but there was no change in the knee adduction moment over time in either group (p > 0.05). The OA group performed the sit-to-stand test more slowly than the control group (p = 0.001). At final testing, functional performance on the sit-to-stand test had improved in the OA group compared to the control group (p = 0.021). The OA group showed a trend towards decreased knee pain (p = 0.05). Conclusion: An 8-week home program of hip abductor muscle strengthening did not reduce knee joint loading, but improved function, in a group of participants with medial knee OA

The purpose of this investigation was to determine the changes in frontal plane kinetics (loading) and neuromuscular responses pre and post unilateral total knee replacement surgery (TKR) during walking. Thirty-four patients with severe knee osteoarthritis (within one week prior to TKR surgery) underwent a gait analysis. 3D kinematics, kinetics and electromyographic (EMG) recruitment patterns from seven lower limb muscles (vastus medialis and lateralis, medial and lateral hamstrings, medial and lateral gastrocnemius and rectus femoris) were recorded while walking at their self-selected walking speed. This was repeated one-year post-TKR surgery. EMG data were normalised to maximum voluntary isometric contractions and the knee adduction moment was normalised to body mass. All waveforms were normalised in time to 100% of the gait cycle. Principal component analysis was applied to the pre-and post-TKR waveforms. T-tests and ANOVA models tested pre-post TKR differences and differences between muscles. At pre-TKR, the average age of the subjects was 66 ± 6.6 years and there were no statistically significant differences between pre and post TKR measures of mass (90Kg). The walking velocity significantly (p< 0.05) increased from the pre-TKR (.9 ±.23 m/s) to the post-TRK (1.07 ±.21 m/s). There were statistically significantly (p< 0.05) magnitude and shape differences between the pre-and-post-TKR waveforms for the knee adduction moment and the EMG waveforms. In general there were reduced adduction moments and EMG amplitudes for quadriceps and hamstrings post-TKR. The results show improved function with the increased walking velocity, but more important are the differences with respect to joint loading and muscle function. The decreased knee adduction moment post-TKR reflects reduced loading on the medial compartment of the prosthesis. The alterations in the quadriceps and hamstrings illustrate that post-TKR the muscles no longer co-activate at high percentage of their maximum during the majority of the gait cycle as was shown in the pre-TKR waveforms. Finally the high lateral hamstring activity found pre-operatively was reduced resulting in a more balanced activation between the medial and lateral sites post operatively. These post-TKR changes have implications for improved joint loading, reduced risk of muscle fatigue and decreased metabolic costs associated with walking

Purpose: To investigate the association between pre-operative gait patterns and the RSA defined migration migration pattern of cemented and uncemented tibial components post total knee arthroplasty (TKA). Method: 43 patients with primary osteoarthritis of the knee underwent Optotrack gait analysis in the week before TKA surgery. Three-dimensional net external knee joint moments and angles were calculated with inverse dynamics. The variability in subject gait patterns was captured with a set of discrete scores that represented weightings on objectively-extracted features of the gait waveform data using principal component analysis. The subjects were randomized to receive the uncemented Nexgen Trabecular metal Monoblock tibial component (n=22; mean age=66 years; mean BMI=32) or the modular cemented cobalt chrome tibial component (n=21; mean age=65 years; mean BMI=33). Both groups were posterior-stabilized and used the same design femoral component. Four experienced surgeons followed a standardized surgical technique and postoperative protocol. Within 4 days of surgery and at 6 months post-operatively, patients had bi-planar knee x-rays taken. RSA analysis was performed with MB-RSA (MEDIS, Leiden). RSA results were reported as maximum total point motion, translations and rotations at 6 months. Spearman’s rank correlations were used to examine the relationship between the first three principle component (PC) scores for each gait variable and the RSA metrics (P< 0.05). Results: There was a highly significant correlation between MTPM and the first principal component (PC) of the knee adduction moment, which represented the overall magnitude of moment during the stance phase of the gait cycle (r=0.459, P=0.005). Higher preoperative knee adduction moment magnitudes were associated with greater MTPM postoperatively. Internal rotation of the components was correlated with the second PC of internal/external rotation moment at the knee, which represented the magnitude of the moment at load acceptance (r=0.341, P=0.042). Greater knee internal rotation moments at load acceptance preoperatively were associated with higher internal rotation postoperatively. Conclusion: The amount of postoperative migration of the tibial component in TKA was found to be correlated with preoperative gait patterns, particularly to the magnitude of the knee adduction moment.. These results suggest that surgical success and prosthesis survivorship may be dependent on the preoperative mechanical environment of the knee joint (i.e., gait)

Background. Alignment and soft tissue (ligament) balance are two variables that are under the control of a surgeon during replacement arthroplasty of the knee. Mobile bearing medial unicompartmental knee replacements have traditionally advocated sizing the prosthesis based on soft tissue balance while accepting the natural alignment of the knee, while fixed bearing prosthesis have tended to correct alignment to a pre planned value, while meticulously avoiding overcorrection. The dynamic loading parameters like peak adduction moment (PKAM) and angular adduction Impulse (Add Imp) have been studied extensively as proxies for medial compartment loading. In this investigation we tried to answer the question whether correcting static alignment, which is the only alignment variable under the control of the surgeon actually translates into improvement in dynamic loading during gait. We investigated the effect of correction of static alignment parameter Hip Knee Ankle (HKA) angle and dynamic alignment parameter in coronal plane, Mean Adduction angle (MAA) on 1st Peak Knee Adduction Moment (PKAM) and Angular Adduction Impulse (Add Imp) following medial unicompartmental knee replacements. Methods. Twenty four knees (20 patients) underwent instrumented gait analysis (BTS Milan, 12 cameras and single Kistler force platform measuring at 100 Hz) before and after medial uni compartmental knee replacement. The alignment was measured using long leg alignment views, to assess Hip Knee Ankle (HKA) angle. Coronal plane kinetics namely 1st Peak Knee Adduction Moment (PKAM) and angular adduction impulse (Add Imp)- which is the moment time integral of the adduction moment curve were calculated to assess medial compartment loading. Single and multiple regression analyses were done to assess the effect of static alignment parameters (HKA angle) and dynamic coronal plane alignment parameters (Mean Adduction Angle – MAA) on PKAM and Add Imp. Results. 12 knees had mobile bearing prosthesis implanted while the other 12 had fixed bearing prosthesis. The mean correction for HKA angle was 2.78 degrees (SD ± 1.32 degrees). There was no significant difference in correction of alignment (HKA) between mobile bearing and fixed bearing groups. MAA and HKA angles were significant predictors of dynamic loading parameters, PKAM and Add Imp (p<0.05). Correction of HKA angle was found to be a better predictor of dynamic loading. We assessed the percentage improvement in loading (%ΔPKAM & %ΔAdd. Imp) and its relationship to correction of HKA (Δ HKA) angle Correction of alignment in the form of HKA (Δ HKA) angle was found to be a very strong predictor of improvement of loads (R = 0.90 for %ΔAdd. Imp and R = 0.50 for %Δ PKAM). Conclusion. Correction of alignment (HKA Angle) predicts improvement in loads through medial compartment of knee. One degree correction resulted in 7% improvement of load through the medial unicompartmental knee replacement

Introduction: Studies have shown a strong relationship between knee osteoarthritis (OA) and the adduction moment at the knee during gait. Total knee arthroplasty (TKA) is known to improve range of motion and function in patients with severe OA. Examinations of tibial bearing wear suggest that although the static alignment of the joint is restored, the abnormal dynamic loading conditions may still remain. The aim of this study was to compare the pre-op and post-op knee biomechanics during gait in patients undergoing TKA. Methods: Gait analysis was performed on 15 patients with 17 TKA’s (8 women and 7 men, all with pre-op varus knee alignment) prior to, 6 months and 1 year following TKA. Reflective markers were placed on the lower extremity of each patient and motion data were collected at 60 Hz using six infrared cameras (Qtrac, Qualysis). Ground reaction forces were recorded at 960 Hz with a multicomponent force plate (Kistler). The frontal plane knee moment (adduction/abduction) was calculated for each trial using inverse dynamics. Based on the anterior/posterior ground reaction force, the stance phase of each trial was divided into a braking phase and a propulsive phase. The area under the knee adduction moment curve (knee adduction impulse) was calculated for each phase. A repeated-measures (Time x Phase) ANOVA was used to compare changes in the peak knee adduction moment and knee adduction impulse for each phase over time. P-values less than 0.05 were considered significant. Results: Mean knee alignment was 4.75 degrees varus pre-op and 4.25 degrees valgus post-op (P < 0.001). A significant time-by-phase interaction was found for peak adduction moment (P = 0.002) and a nearly significant time-by-phase interaction was found for adduction impulse (P = 0.056). In braking phase, six months after surgery, knee adduction impulse and peak moment decreased 26% and 15% respectively. At one year, however, both increased by 20% and 19% respectively to near pre-op levels. In propulsive phase, knee adduction impulse and moment decreased 34% and 25% respectively at 6 months but only increased by 4% and 11% respectively at one year follow-up. Knee Society and Function scores improved from 50.17 and 61.67 pre-op to 82.08 and 82.50 at 6 months and 88.83 and 85.83 at 1 year post-op (P < 0.001, respectively). Discussion: After TKA, in the breaking phase of gait, the initial improvement in knee adduction impulse and peak knee adduction moment noted at 6 months disappeared completely indicating no improvement in medial compartment loading conditions at 1 year post operatively. The improvement in these parameters during the propulsive phase remained persistent at 1 year although there was some tendency to revert back to pre-operative levels. This would suggest that restoration of anatomic axial alignment and soft tissue balance do not change the medial loading conditions following TKA

The MediShoe (Promedics Orthopaedics Ltd, Glasgow) is a specific post-operative foot orthosis used by post-operative foot and ankle patients designed to protect fixations, wounds and maximise comfort. The use of rigid-soled shoes has been said to alter joint loading within the knee and with the popular use of the MediShoe at our centre in post operative foot and ankle surgery patients, it is important to ascertain whether this is also true. An analysis of the knee gait kinetics in healthy subjects wearing the MediShoe was carried out. Ten healthy subjects were investigated in a gait lab both during normal gait (control) and then with one shoe orthosis worn. Force plates and an optoelectronic motion capture system with retroreflective markers were used and placed on the subjects using a standardised referencing system. Three knee gait kinetic parameters were measured:- knee adduction moment; angle of action of the ground reaction force with respect to the ground in the coronal plane as well as the tibiofemoral angle. These were calculated with the Qualisys software package (Gothenburg, Sweden). A two-tailed paired t-test (95% CI) showed no significant difference between the control group and the shoe orthosis-fitted group for the knee adduction moment (p = 0.238) and insignificant changes with respect to the tibiofemoral angle (p = 0.4952) and the acting angle of the ground reaction force (p = 0.059). The MediShoe doesn't significantly alter knee gait kinetics in healthy patients. Further work, however is recommended before justifying its routine use

Background. Constitutional knee varus increases the risk of medial OA disease due to increase in the knee adduction moment and shifting of the mechanical axis medially. Hueter-Volkmann's law states that the amount of load experienced by the growth plate during development influences the bone morphology. For this reason, heightened sports activity during growth is associated with constitutional varus due to added knee adduction moment. In early OA, X-rays often show a flattened medial femoral condyle extension facet (EF). However, it is unknown whether this is a result of osteoarthritic wear, creep deformation over decades of use, or an outcome of Hueter-Volkmann's law during development. A larger and flattened medial EF can bear more weight, due to increased load distribution. However, a flattened EF may also extrude the meniscus, leading meniscus degeneration and joint failure. Therefore, this study aimed to investigate whether varus knees have flattened medial EFs of both femur and tibia in a cohort of patients with no signs yet of bony attrition. Methods. Segmentation and morphology analysis was conducted using Materialise software (version 8.0, Materialise Inc., Belgium). This study excluded knees with bony attrition of the EFs based on Ahlbäck criteria, intraoperative findings, and operation notes history. Standard reference frames were used for both the femur and tibia to ensure reliable and repeatable measurements. The hip-knee-angle (HKA) angle defined varus or valgus knee alignment. Femur: The femoral EFs and flexion facets (FFs) had best-fit spheres fitted with 6 repetitions. (Fig1). Tibia: The slopes of the antero-medial medial tibial plateau were approximated using lines. (fig2). Results. 72 knees met the inclusion and exclusion criteria. The average age was 59 ± 11 years. The youngest was 31 and the oldest 84 years. Thirty-three were male and 39 were female. There was good intra- and inter-observer reliability for EF sphere fitting. Femur: The results demonstrated that the medial femoral condyle EF is flattened in knees with constitutional varus, as measured by the Sphere Ratios between the medial and lateral EF (varus versus straight: p = 0.006), and in the scaled values for the medial EF sphere radius (varus versus straight: p = 0.005). There was a statistically significant, moderate and positive correlation between the medial femoral EF radius, and the medial femoral EF-FF AP offset. (fig3). Tibia: There was a statistically significant difference between the steepness of the slopes of the medial tibial plateau EF in varus and valgus knees, suggesting varus knees have a less concave (flatter) medial EF. (fig3). Conclusions. In comparison to straight knees, varus knees have flattened medial EFs in both femur and tibia. As this was the case in knees with no evidence of bony attrition, this could mean flattened medial EFs may be a result of medial physis inhibition during development, due to Hueter-Volkmann's law. Flattened medial EFs may increase load distribution in the medial compartment, but could also be a potential aetiology in primary knee OA due to over extrusion of the medial meniscus and edge loading

Constitutional knee varus increases the risk of medial OA disease due to increase in the knee adduction moment and shifting of the mechanical axis medially. Hueter-Volkmann’s law states that the amount of load experienced by the growth plate during development influences the bone morphology. For this reason, heightened sports activity during growth is associated with constitutional varus due to added knee adduction moment. In early OA, X-rays often show a flattened medial femoral condyle extension facet (EF). However, it is unknown whether this is a result of osteoarthritic wear, creep deformation over decades of use, or an outcome of Hueter-Volkmann’s law during development. A larger and flattened medial EF can bear more weight, due to increased load distribution. However, a flattened EF may also extrude the meniscus, leading meniscus degeneration and joint failure. Therefore, this study aimed to investigate whether varus knees have flattened medial EFs of both femur and tibia in a cohort of patients with no signs yet of bony attrition. Segmentation and morphology analysis was conducted using Materialise software (version 8.0, Materialise Inc., Belgium). This study excluded knees with bony attrition of the EFs based on Ahlbäck criteria, intraoperative findings, and operation notes history. Standard reference frames were used for both the femur and tibia to ensure reliable and repeatable measurements. The hip-knee-angle (HKA) angle defined varus or valgus knee alignment. Femur: The femoral EFs and flexion facets (FFs) had best-fit spheres fitted with 6 repetitions. Tibia: The slopes of the antero-medial medial tibial plateau were approximated using lines. Results 72 knees met the inclusion and exclusion criteria. The average age was 59 ± 11 years. The youngest was 31 and the oldest 84 years. Thirty-three were male and 39 were female. There was good intra- and inter-observer reliability for EF sphere fitting. Femur: The results demonstrated that the medial femoral condyle EF is flattened in knees with constitutional varus, as measured by the Sphere Ratios between the medial and lateral EF (varus versus straight: p = 0.006), and in the scaled values for the medial EF sphere radius (varus versus straight: p = 0.005). There was a statistically significant, moderate and positive correlation between the medial femoral EF radius, and the medial femoral EF-FF AP offset. Tibia: There was a statistically significant difference between the steepness of the slopes of the medial tibial plateau EF in varus and valgus knees, suggesting varus knees have a less concave (flatter) medial EF. Conclusions In comparison to straight knees, varus knees have flattened medial EFs in both femur and tibia. As this was the case in knees with no evidence of bony attrition, this could mean flattened medial EFs may be a result of medial physis inhibition during development, due to Hueter-Volkmann’s law. Flattened medial EFs may increase load distribution in the medial compartment, but could also be a potential aetiology in primary knee OA due to over extrusion of the medial meniscus and edge loading

Introduction. Although Total Knee Arthroplasty (TKA) has been shown to correct abnormal frontal plane knee biomechanics, little is known about this effect beyond 6 months. The purpose of this study was to compare sequentially the knee adduction moment during level-walking before and after TKA in varus knees. We hypothesized that adduction moment would diminish after TKA proportionate to the tibio-femoral realignment in degrees. Methods. Fifteen patients (17 TKA's) with varus knees were prospectively enrolled and gait analysis performed prior to, 6 months and 1 year following TKA. Reflective markers were placed on the lower extremity and motion data collected using six infrared cameras (Qtrac, Qualysis). Ground reaction forces were recorded with a multicomponent force plate (Kistler). A repeated-measures ANOVA was used to compare changes in the peak adduction moment and peak dynamic varus angle over time. Results. TKA corrected static knee alignment from 2.2 (2.5) degrees varus to 3.5 (2.7) degrees valgus (P < 0.001). Peak dynamic varus angle during gait was reduced from 9.7 (6.5) degrees to 3.6 (5.8) degrees at 6 months and 5.2 (7.6) degrees at 1 year (Main Effect of Time; P=0.005). Peak adduction moment was significantly reduced to 85% of pre-op level at 6 months (P=0.037) but subsequently increased to 94% of pre-op level at 1 year (P = 0.539). Post-op improvement in static alignment did not correlate with the change in adduction moment at any follow-up period (P = 0.671). A significant correlation was found between the increase in dynamic varus angle and the subsequent increase in adduction moment from the six-month to the one-year follow-up (P = 0.008). Conclusion. TKA improves knee adduction moment at 6 months but this effect is lost with time (1 year). Despite restoration of static knee alignment and soft tissue balance, loading conditions at medial compartment remain high, predisposing to medial polyethylene wear, a finding reported by retrieval studies

Purpose: The purpose of this study was to determine what differences exist in the knee flexion, rotation and adduction moments and periarticular knee muscle activation patterns between subjects with medial compartment knee osteoarthritis (OA) and those with lateral compartment knee OA. Method: Forty eight individuals with knee OA were studied. The group was divided into those with predominantly medial compartment involvement (38 subjects, age 63 ± 8 years) and those with lateral involvement (10 subjects, age 63 ± 9 years). Three-dimensional motion (Optotrak) and ground reaction force (AMTI) data were collected while the subjects walked at a self-selected velocity. The knee flexion, rotation and adduction moments, time normalized to the percentage of one gait cycle, were calculated using an inverse dynamics approach. Electromyograms (EMG) were also collected from the rectus femoris, vastus lateralis, vastus medialis, medial and lateral hamstrings, and medial and lateral gastrocnemius and normalized to maximum voluntary isometric contractions. Knee moments and waveforms for each muscle for one complete gait cycle were analyzed for group differences using principal component analysis (PCA) followed by Student’s t-tests (alpha-adj = 0.017) for the PCA scores. Results: The two groups were statistical similar in terms of age, height, weight, and walking velocity (p> 0.05). PCA analysis revealed statistically significant differences (p< 0.017) in patterns for the knee adduction moment, medial gastrocnemius, and lateral hamstrings between the two groups. Conclusion: As expected, there was a difference in the knee adduction moment between the two groups. What is novel is that the muscle activation patterns from the lateral site group are consistent with an attempt to unload that compartment. The results of this study provide evidence that biomechanical and neuromuscular differences do exist, depending on the OA site. This could have implications for developing site-specific conservative management approaches

Abstract. OBJECTIVES. Valgus high tibial osteotomy (HTO) represents an effective treatment for patients with medial compartment osteoarthritis (OA) in a varus knee. However, the mechanisms which cause this clinical improvement are unclear. Previous studies suggest a wider stance gait can reduce medial compartment loading via reduction in the external knee adduction moment (KAM); a measure implicated in progression of medial compartment OA. This study aimed to measure whether valgus HTO is associated with a postoperative increase in static stance width. METHODS. 32 patients, recruited in the Biomechanics and Bioengineering Centre Versus Arthritis HTO study, underwent valgus (medial opening wedge) HTO. Weightbearing pre- and post- operative radiographs were taken showing both lower limbs. The horizontal distance, measured from a fixed point on the right talus to the corresponding point on the left, was divided by the talus width to give a standardised “stance width” for each radiograph. The difference between pre- and post- operative stance width was compared for each patient using a paired sample t-test. RESULTS. Preoperatively, mean stance was 4.00 talar-widths but postoperatively this increased to 5.41. This mean increase of 1.42 talar-widths was statistically significant (p=0.001) and represents a mean proportional increase in stance width of 35.5% following HTO. Of the 32 patients, 23 showed increased stance width and 9 decreased (range −4.64 to 6.00 talar-widths). CONCLUSIONS. These findings indicate an association of frontal plane surgical realignment at the proximal tibia via a medial opening wedge HTO with an increased stance width on postoperative radiographs. Considering both wider stance gait and HTO have been shown to affect the progression of medial compartment OA, these results may explain one mechanism contributing to the efficacy of HTO surgery. However, the range of changes in stance width suggests significant variability in how patients adapt at a whole-limb and whole-body level following HTO. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project