Muscle Forces during Weightbearing Exercises in Medial Knee Osteoarthritis and Varus Malalignment: A Cross-sectional Study

To test the hypothesis that common weightbearing exercises generate higher lower-limb muscle forces but do not increase medial tibiofemoral contact force (MTCF) when compared to walking in people with medial knee osteoarthritis and varus malalignment. Twenty-eight participants aged ≥50 years with medial knee osteoarthritis and varus malalignment were recruited from the community. Three-dimensional lower-body motion, ground reaction forces and surface electromyograms from 12 lower-limb muscles were acquired during five squat, lunge, single-leg heel raise and walking trials, performed at self-selected speeds. An electromyogram-informed neuromusculoskeletal model with subject-specific bone geometry was used to estimate muscle forces (N) and bodyweight (BW) normalised MTCF. The peak forces for muscle groups (knee extensors, knee flexors, ankle plantar flexors and hip abductors) and peak MTCF were compared to walking using a multivariate analysis of variance model. There was a significant main effect (p < 0.001). Post-hoc tests (mean difference [95% confidence intervals]) showed that compared to walking, participants generated higher peak knee extensor and flexor forces during squatting (extensor: 902 N [576, 1227], flexor: 192 N [9.39, 375]) and lunging (extensor: 917 N [604, 1231], flexor: 496 N [198, 794]), and lower peak hip abductor force during squatting (-1975 N [-2841, -1108]) and heel raises (-1217 N [-2131, -303]). Compared to walking, MTCF was lower during squatting (-0.79 BW [-1.04, -0.53]) and heel raises (-0.27 BW [-0.50, -0.04]). No other significant differences were observed. Participants generated higher peak knee flexor and extensor forces during squatting and lunging but did not increase peak MTCF compared to walking. Clinicians can use these findings to reassure themselves and patients that weightbearing exercises in these positions do not adversely increase forces within the osteoarthritic joint compartment.