Muscle strength, physical performance and physical activity as predictors of future knee replacement: a prospective cohort study

Objective: To investigate associations between lower levels of muscle strength, physical performance and physical activity and the risk of knee replacement (KR) in older adults with frequent knee pain.

Method: Participants from the Multicenter Osteoarthritis Study (MOST) with knee pain on most of the past 30 days at baseline were included (n = 1257; mean (SD) age of 62.2 (8.2)). We examined the association between (1) baseline peak isokinetic knee extensor strength, (60°/sec, maximum out of four trials), (2) best time to stand in timed chair stand (2 trials of five repetitions), and (3) baseline Physical Activity Scale for the Elderly score (PASE) with incident KR between baseline and the 84-month follow-up.

Results: 1252 (99.6%) participants (1682 knees) completed the follow-up visits. 331 participants (394 knees) underwent a KR during the 84 months (229 women and 102 men). The crude analysis demonstrated a decreased risk of KR in women (P < 0.0001) with higher knee extensor strength (Hazard Ratio (HR; 95% CI) 0.99 (0.98-0.99)). The risk remained significant (P = 0.03) when adjusting for age, BMI, race, clinic site, education, occupation, previous knee injury, previous knee surgery, and WOMAC pain (HR (95% CI) 0.99 (0.99-1.00)), but not when adjusting for Kellgren-Lawrence grade (P = 0.97).

Conclusion: Lower levels of chair stand performance and self-reported physical activity are not associated with an increased risk of KR within 7 years, while the independent effect of knee extensor strength on risk for KR in women is non-significant after adjusting for radiographic severity.