In knee OA , strong evidence was found that avoidance of activities is associated with activity limitations via muscle weakness ( mediation by muscle weakness ) , strong evidence was found for an association between muscle weakness and activity limitations , and weak evidence was found that pain and psychological distress are associated with muscle weakness via avoidance of activities ( mediation by avoidance ) .
In hip OA , weak evidence was found for mediation by muscle weakness ; and strong evidence was found for an association between muscle weakness and activity limitations .
The avoidance model in patients with knee and hip osteoarthritis ( OA ) hypothesizes that pain and psychological distress lead to avoidance of activities , and thereby to muscle weakness and activity limitations .
This paper systematic ally review s the scientific evidence for the validity of this avoidance model .
Physical function and properties of quadriceps femoris muscle in men with knee osteoarthritis.
OBJECTIVES To examine the objective physical function of the lower extremities , to measure the properties of quadriceps femoris muscle ( QFM ) , and to assess subjective disabilities in men with knee osteoarthritis ( OA ) and to compare the results with those obtained from age- and sex-matched control subjects . DESIGN Cross-sectional study . SETTING Rehabilitation clinic in a university hospital . PARTICIPANTS Male volunteers ( n=54 ) ( age range , 50 - 69y ) with knee OA and r and omly selected healthy , age- and sex-matched control subjects ( n=53 ) . INTERVENTIONS Not applicable . MAIN OUTCOME MEASURES Physical function evaluated with a test battery including the QFM composition measurement , the Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) , and the R AND 36-Item Short-Form Health Survey , version 1.0 .  RESULTS Knee OA patients had 13 % to 26 % poorer ( P range , .050-.001 ) physical function and muscle strength compared with the controls . There were also significant differences in QFM composition . WOMAC ( P range , .050-.001 ) and muscle strength ( P<.001 ) associated with physical function tests , but subjective pain correlated with neither physical function nor muscle strength in knee OA patients . The radiographic knee OA grade did not have any significant effect on physical function , but passive knee motion , knee extension strength , and WOMAC were related to the severity of the disease ( P<.05 ) . CONCLUSIONS The patients with knee OA exhibited impaired physical function and muscle strength and QFM composition compared with healthy controls . The severity of radiographic knee OA clearly had adverse effects on functional ability at the later stages of the disease . The results highlight the effect of QFM strength on physical function as well as the importance of patient 's subjective and objective physical function when deciding on knee OA treatment policy
In knee OA , strong evidence was found that avoidance of activities is associated with activity limitations via muscle weakness ( mediation by muscle weakness ) , strong evidence was found for an association between muscle weakness and activity limitations , and weak evidence was found that pain and psychological distress are associated with muscle weakness via avoidance of activities ( mediation by avoidance ) .
In hip OA , weak evidence was found for mediation by muscle weakness ; and strong evidence was found for an association between muscle weakness and activity limitations .
The avoidance model in patients with knee and hip osteoarthritis ( OA ) hypothesizes that pain and psychological distress lead to avoidance of activities , and thereby to muscle weakness and activity limitations .
This paper systematic ally review s the scientific evidence for the validity of this avoidance model .