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 .
Development and validation of a lower-extremity activity scale. Use for patients treated with revision total knee arthroplasty.
BACKGROUND Valid outcome measurement tools are required to reliably demonstrate the effectiveness and clinical outcomes of lower-extremity arthroplasty . Having ascertained a lack of a practical and valid measure of the change in actual daily physical activity that occurs prior to and following lower-limb arthroplasty , we developed and vali date d a lower-extremity activity scale . METHODS The eighteen-level self-administered scale was developed with the aid of content experts to ensure face validity . Validity and reliability were assessed with the use of ( 1 ) pedometer measurements of seventy subjects over seven days ;  ( 2 )  next-of-kin proxy measurements of the activity levels of ninety patients before they underwent lower-limb arthroplasty ;  and ( 3 ) application , and correlation with the Western Ontario and McMaster Universities Osteoarthritis Index scores , in a prospect i ve seventeen-center clinical study of 297 consecutive patients undergoing revision total knee arthroplasty . In this latter study , demographic and comorbidity data were also collected . Univariate and bivariate correlations were performed , and a multivariate structured equation modeling approach was used to further test responsiveness , reliability , and validity of the lower-extremity activity scale . RESULTS Pedometer readings correlated with the activity levels derived with the lower-extremity activity scale ( r = 0.79 ) . Of note was the finding that age , weight , and body mass index did not correlate well with the average number of steps per day ( r = -0.32 , -0.32 , and -0.25 , respectively ) . A significant correlation was found between the lower-extremity activity scores recorded by the patients and those reported by their next of kin ( Pearson correlation , r = 0.715 ; p = 0.0001 ) and between the initial lower-extremity activity scores and two-week-retest scores ( intraclass correlation = 0.9147 ; p < 0.0001 ) , demonstrating the validity and reliability of the scale . The  lower-extremity activity scale was responsive , accurately reflecting changes in the patient 's condition between baseline and the time of follow-up ( p < 0.001 ) , and it was reliable , with baseline values correlating with follow-up scores ( p < 0.001 ) . The convergent validity of the lower-extremity activity scale was established by correlations with the function scores ( r = -0.301 , p < 0.001 ) and pain scores ( r = -0.241 , p < 0.001 ) derived with the Western Ontario and McMaster Universities Osteoarthritis Index and with a higher number of comorbidities ( r = -0.244 , p < 0.001 ) . Multivariate path modeling further demonstrated diminished activity in patients who had more difficulty in functioning and a greater number of comorbidities . CONCLUSIONS We developed a lower-extremity activity scale and vali date d that it was an effective instrument for the assessment of patients ' actual activity levels . It is easy to apply and interpret , and it is valid and ready for use in the clinical setting . This scale will allow more accurate analysis and prediction of outcomes . Consequently , it will become a useful , practical adjunct to objective clinical decision-making and intervention for patients undergoing arthroplasty
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 .