An investigation of the validity of six measures of physical function in people awaiting joint replacement surgery of the hip or knee.
OBJECTIVE
To assess and compare the validity of six physical function measures in people awaiting hip or knee joint replacement.


METHODS
Eighty-two people awaiting hip or knee replacement were assessed using six physical function measures including the WOMAC Function scale, SF-36 Physical Function scale, SF-36 Physical Component Summary scale, Patient Specific Functional Scale, 30-second chair stand test, and 50-foot timed walk. Validity was assessed using a head-to-head comparison design.


RESULTS
Convergent validity was demonstrated with significant correlations between most measures (Spearman's rho 0.22 to 0.71). The Patient Specific Functional Scale had the lowest correlations with other measures of physical function. Discriminant validity was demonstrated with low correlations between mental health and physical function scores (Spearman's rho -0.12 to 0.33). Only the WOMAC Function scale, 30-second chair stand test, and 50-foot timed walk demonstrated known groups validity when scores for participants who walked with a gait aid were compared with those who did not. Standardized response means and Guyatt's responsiveness indexes indicated that the SF-36 was the least responsive measure.


CONCLUSIONS
For those awaiting joint replacement surgery of the hip or knee, the current investigation found that the WOMAC Function scale, 30-second chair stand test, and 50-foot timed walk demonstrated the most evidence of validity. The Patient Specific Functional Scale might complement other measures by capturing a different aspect of physical function.
Barwon Health, Australia. steveg@barwonhealth.org.au
Stephen D
SD
Gill
Natalie A
NA
de Morton
Helen
H
Mc Burney
D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000175:diagnosis / Q000534:rehabilitation / Q000601:surgery; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000534:rehabilitation / Q000601:surgery; D010808:Physical Examination / Q000379:methods; D010809:Physical Fitness / Q000502:physiology*; D011300:Preoperative Care / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D014850:Waiting Lists