Avoidance of activity and disability in patients with osteoarthritis of the knee: the mediating role of muscle strength.
OBJECTIVE
Avoidance of activity is hypothesized to lead to muscle weakness and consequently, to physical disability. This study was undertaken to validate the avoidance model by providing evidence for the mediating role of muscle weakness in the relationship between avoidance of activity and physical disability in patients with osteoarthritis (OA) of the knee.


METHODS
Data on avoidance of activity, observed physical disability, and muscle strength of the knee in 107 patients with knee OA were analyzed. A series of regression analyses was performed to establish the mediating role of muscle weakness. First, the effect of avoidance of activity on the level of disability was assessed. Next, the relationship between avoidance of activity and muscle strength was established. Finally, the mediating role of muscle strength could be established if the effect of avoidance of activity on disability decreased when muscle strength was taken into account.


RESULTS
Initially, avoidance of activity accounted for 21.5% of variance in disability. Avoidance of activity also accounted for 3.9% of variance in muscle strength. After muscle strength was taken into account, the variance in disability accounted for by avoidance of activity was reduced from 21.5% to 15.7%. Thus, the criteria for establishing the mediating role of muscle strength were met.


CONCLUSIONS
The results of this study provide evidence for the mediating role of muscle weakness in the relationship between avoidance of activity and disability in patients with knee OA.
Netherlands Institute of Health Services Research, Utrecht, The Netherlands. m.steultjens@nivel.nl
M P M
MP
Steultjens
J
J
Dekker
J W J
JW
Bijlsma
D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D005082:Physical Exertion / Q000502:physiology*; D012044:Regression Analysis