Quadriceps weakness in knee osteoarthritis: the effect on pain and disability

Abstract

Objectives: (1) To determine the importance of quadriceps strength, structural change, and psychological status in terms of knee pain in the community. (2) To determine the relative importance of quadriceps function, structural change, and psychological status with respect to disability in subjects with knee pain.

Methods: 300 men and women with pain and 300 controls without pain (aged 40-79) were seen. Isometric quadriceps strength (MVC) was measured and muscle activation was assessed by twitch superimposition. Disability (Western Ontario McMaster Osteoarthritis Index (WOMAC)) and anxiety and depression were assessed (Hospital Anxiety and Depression Index (HAD)). Radiographs were obtained of the tibiofemoral and patellofemoral joints and total score for osteophyte, 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 analysed by multiple logistic regression: quadriceps strength (odds ratio 18.8, CI 4.8, 74.1 for MVC < or = 10 kgF); depression (odds ratio 2.4, CI 1.0, 5.5 for HAD score > or = 8); and radiographic change (odds ratio 4.1, CI 1.9, 8.6 for radiographic score > or = 4) were independently associated with pain. In those with knee pain, disability was independently associated with quadriceps strength (odds ratio 8.2, CI 1.5, 44.4 for MVC < or = 10 kgF) and depression (odds ratio 6.2, CI 2.1, 18.0 for HAD score > or = 8); but not with radiographic score.

Conclusions: Quadriceps strength is strongly associated with knee pain and disability in the community, even when activation and psychological factors are taken into account. This has important therapeutic implications.

Figure 1

Mean maximum voluntary strength (MVC) and mean predicted strength (MPC) for right and left quadriceps in cases (subjects with knee pain) and controls (subjects without knee pain). Error bars denote 95% confidence intervals.

Figure 2

Percentage of subjects with knee pain by level of radiographic score (highest score for each subject from right or left knee). Error bars represent 95% confidence intervals. n=total number of subjects in each group.

Figure 3

Prevalence of anxiety and depression (HAD score ⩾8) for men and women with knee pain (cases) and without knee pain (controls). Errors bars represent 95% confidence intervals. n=total number of subjects in each group.

Figure 4

Percentage of knee pain positive subjects with disability (WOMAC function score >19) by level of quadriceps strength (lowest value for each subject for right or left knee). Results are presented separately for men aged 60-80 (n=63), men aged 40-59 (n=42), women aged 60-80 (n=109) and women aged 40-59 (n=84).