QUADRICEPS WEAKNESS IN KNEE OSTEOARTHRITIS - THE EFFECT ON PAIN AND DISABILITY

Objectives - (1) To determine the importance of quadriceps strength, s tructural change, and psychological status in terms of knee pain in th e community. (2) To determine the relative importance of quadriceps fu nction, structural change, and psychological status with respect to di sability in subjects with knee pain. Methods - 300 men and women with pain and 300 controls without pain (aged 40-79) were seen. Isometric q uadriceps strength (MVC) was measured and, muscle activation was asses sed by twitch superimposition. Disability (Western Ontario McMaster Os teoarthritis Index (WOMAC)) and anxiety and depression were assessed ( Hospital Anxiety and Depression Index (HAD)). Radiographs were obtaine d of the tibiofemoral and patellofemoral joints and total score for os teophyte, narrowing, and sclerosis calculated for each knee. Results - Subjects with knee pain had lower voluntary quadriceps strength than those without pain (p < 0.005). Quadriceps activation was also lower ( p < 0.005),but did not fully explain the reduction in strength. When a nalysed by multiple logistic regression: quadriceps strength (odds rat io 18.8, CI 4.8, 74.1 for MVC less than or equal to 10 kgF); depressio n (adds ratio 2.4, CI 1.0, 5.5 for HAD score greater than or equal to 8); and radiographic change (odds ratio 4.1, CI 1.9, 8.6 for radiograp hic score greater than or equal to 4) were independently associated wi th pain. In those with knee pain, disability was independently associa ted with quadriceps strength (odds ratio 8.2, CI 1.5, 44.4 for MVC les s than or equal to 10 kgF) and depression (odds ratio 6.2, CI 2.1, 18. 0 for HAD score greater than or equal to 8); but not with radiographic score. Conclusions - Quadriceps strength is strongly associated with knee pain and disability in the community, even when activation and ps ychological factors are taken into account. This has important therape utic implications.