Abstract
BACKGROUND: This study examined whether individuals who have mild medial osteoarthritis (OA) of the knee with coexisting lateral OA have less muscle strength than individuals who do not have lateral OA. METHODS: A series of 153 individuals (84% of whom were women) between 48 and 88 years old who had Kellgren and Lawrence (KL) grade-2 OA in the medial compartment of the knee underwent radiographic evaluation to assess the presence of lateral OA, which was graded with the system of the Osteoarthritis Research Society International (OARSI) atlas as well as the KL system. The isometric maximum strengths of the quadriceps, the hip abductors, and the hip extensors were evaluated with use of a handheld dynamometer. RESULTS: Individuals who had coexisting medial and lateral OA had more severe knee pain and weaker quadriceps than those who did not have lateral OA. The study adjusted for age and sex both for the OARSI atlas system (adjusted difference in mean strength: 0.272 Nm/kg, 95% confidence interval [CI]: 0.143 to 0.401 Nm/kg) and for KL grading (adjusted difference in mean strength: 0.185 Nm/kg, 95% CI: 0.061 to 0.309 Nm/kg). Logistic regression analysis showed that weakness of the quadriceps increased the odds of the presence of lateral OA sevenfold after adjustments using the OARSI atlas were made for age, sex, anatomical axis, range of motion of the knee, and intensity of pain in the knee. CONCLUSIONS: Individuals who had coexisting medial and lateral OA had weaker quadriceps than individuals who had mild medial OA alone. Paying close attention to quadriceps weakness might provide a key to clarifying the pathogenesis of bicompartmental disease in the tibiofemoral joint. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.