The Effects of Quadriceps Weakness on the Knee Adductor Moment During Gait

Abstract

0356 A high knee adductor moment has been shown to exacerbate the progression of knee osteoarthritis (OA). Mechanical alignment of the lower limb is correlated with a high adductor moment. Alternatively, conservative treatment consisting of quadriceps strengthening minimizes progression of the disease, reduces pain and improves gait function. Thus, mechanical alignment and quadriceps weakness often co-exist in knee OA populations and the effect of quadriceps strengthening on gait function in this patient population is often confounded by the OA disease process itself. PURPOSE: To isolate the effect of quadriceps weakness on the adductor moment during the stance phase of gait, independent of alignment or OA severity. METHODS: Using an intra-articular knee insufflation technique, quadriceps strength was inhibited (≥ 20% of MVC as measured via Cybex isometry at 30°) and its effects on gait function were assessed in an otherwise healthy population (N = 10, who exhibit normal ranges of mechanical alignment) using traditional 3D gait analysis. RESULTS: Under speed controlled conditions, quadriceps weakness caused a significant increase in the peak knee adductor moment, a decrease in the knee midstance ROM, and medial change in the position of the Fy GRF (all P < 0.04). There were no changes in step width, stride length, foot progression angle, hip or ankle ROM, peak F1 vertical ground reaction force (VGRF) or loading rate of F1 VGRF (all P > 0.05). The peak adductor moment was best predicted by the mechanical alignment of the lower extremity (r = .88, p < 0.01) in pre-insufflation trials. However, the change in quadriceps strength was highly correlated with the change in adductor moment (semi-partial r = .84, p < 0.01) over and above alignment (semi-partial r = .25, p = 0.48) in post-insufflation trials. CONCLUSION: Mechanical alignment may better predict the adductor moment, but quadriceps weakness may exacerbate it's magnitude in unhealthy populations such as those with knee OA.