Validation of a short form of the Western Ontario and McMaster Universities Osteoarthritis Index function subscale in hip and knee osteoarthritis.
OBJECTIVE
A short version of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function scale has recently been developed to enhance the applicability of the scale in routine practice and clinical research for patients with hip and knee osteoarthritis. The goal of the present study was to validate this short form.


METHODS
We conducted a prospective 4-week cohort study of 1,036 outpatients. Performance on the WOMAC function long form (LF) and short form (SF) was compared. Agreement between responses on the 2 forms was examined according to a Bland-Altman plot. Responsiveness to change (by standardized response mean [SRM]), reproducibility (intraclass correlation coefficient [ICC]), and internal consistency (Cronbach's alpha) were computed for both forms. Construct validity was assessed based on functional impairment as measured on a numerical rating scale.


RESULTS
At baseline, 24% of patients who completed the WOMAC LF had missing data for at least 1 item as compared with only 6% of patients who completed the WOMAC SF. The mean WOMAC SF score was greater than the mean WOMAC LF score (mean +/- SD difference -4.3 +/- 4.8 on a 0-100 scale). SRMs were 0.61 and 0.73, ICCs were 0.76 and 0.68, and Cronbach's alphas were 0.93 and 0.85 for the WOMAC LF and SF, respectively. The 2 forms had comparable correlation with functional impairment.


CONCLUSIONS
The WOMAC function short form has a low rate of missing data and is a responsive, reproducible, and valid measure. The mean SF score was 4 points higher than the mean LF score.
Baron
Gabriel
G
AP-HP, Hôpital Bichat, Département d'Eidémiologie, Biostatistique et Recherche Clinique, INSERM, U738, Paris, France. gabriel.baron@bch.aphp.fr
Tubach
Florence
F
Ravaud
Philippe
P
Logeart
Isabelle
I
Dougados
Maxime
M
D000368:Aged; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D010045:Outpatients; D011446:Prospective Studies; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*