[Metric properties of WOMAC questionnaires-original and reduced versions-to measure symptoms and Physical Functional Disability]

Abstract

Objectives: To determine the metric properties of the WOMAC questionnaire filled in over the telephone; and to obtain a reduced version of this questionnaire.

Design: Descriptive study.

Setting: "La Merced" (Osuna. Seville) and "Torrecárdenas" (Almeria) Hospitals.

Participants: People suffering from hip and knee osteoarthritis and awaiting surgical intervention from October 2004 to November 2006.

Main measurements: Telephone interview, sociodemographic variables and Symptoms and Physical Functional Disability (WOMAC questionnaire) were collected.

Results: A total of 311 people suffering from hip or knee osteoarthritis were included. Subjects were mostly women (82.63%) with a mean age of 70 years. Metric properties of the original and reduced WOMAC were as follows: All WOMAC items obtained a maximum value of 67.4% on endorsement frequency. Main components factorial analysis resulted in a communality of over 0.5 and 71.73% of total explained variance, with 5 factors -no conceptual meaning-. With a communality cut-off point of 0.8; 13 items were rejected and the total explained variance increased to 87.74% with 4 factors -conceptually sensible-. Varimax rotations were performed due to low correlation factors. Pearson correlation between the original and reduced WOMAC versions were 0.92. Reliability analysis obtained a Cronbach alpha value of 0.92 for original WOMAC and 0.82 for the reduced version.

Conclusion: The original WOMAC questionnaire showed adequate metric properties to be used over the telephone on people suffering from hip and knee osteoarthritis. Furthermore, a reduced version of WOMAC with 11 items had better metric properties than the full version.

Figures

Figura 1

Cuestionario WOMAC.

Figura 2

Diagrama de puntos entre el cuestinario WOMAC 24 y el cuestionario WOMAC 11.