Knee Power Is an Important Parameter in Understanding Medial Knee Joint Load in Knee Osteoarthritis

OBJECTIVE To determine the extent to which knee extensor strength and power explain variance in knee adduction moment (KAM) peak and impulse in clinical knee osteoarthritis (OA). METHODS Fifty-three adults (mean ± SD age 61.6 ± 6.3 years, 11 men) with clinical knee OA participated. The KAM waveform was calculated from motion and force data and ensemble averaged from 5 walking trials. The KAM peak was normalized to body mass (Nm/kg). The mean KAM impulse reflected the mean total medial knee load during stride (Nm × seconds). For strength, the maximum knee extensor moment attained from maximal voluntary isometric contractions (MVIC) was normalized to body mass (Nm/kg). For power, the maximum knee extensor power during isotonic contractions, with the resistance set at 25% of MVIC, was normalized to body mass (W/kg). Covariates included age, sex, knee pain on the Knee Injury and Osteoarthritis Outcome Score, gait speed, and body mass index (BMI). Relationships of the KAM peak and impulse with strength and power were examined using sequential stepwise forward linear regressions. RESULTS Covariates did not explain variance in the KAM peak. While extensor strength did not, peak knee extensor power explained 8% of the variance in the KAM peak (P = 0.02). Sex and BMI explained 24% of the variance in the KAM impulse (P < 0.05). Sex, BMI, and knee extensor power explained 31% of the variance in the KAM impulse (P = 0.02), with power contributing 7% (P < 0.05). CONCLUSION Knee extensor power was more important than isometric knee strength in understanding medial knee loads during gait.