Impact of comorbidities on the measurement of health in patients with ankle osteoarthritis

Background: Investigators seeking to understand the impact of musculoskeletal disorders commonly use validated outcome instruments to assess the effect of diseases on physical function and quality of life. However, the influence of concomitant systemic or musculoskeletal comorbidities on these scores has not been widely considered in orthopaedic research. The purpose of this study was to determine how morbidity unrelated to the ankle influences the perception of physical function and pain by patients with ankle osteoarthritis. Methods: Short Form-36 (SF36) Physical Component Summary (PCS) and Mental Component Summary (MCS) scores, Ankle Osteoarthritis Scale (AOS) pain scale scores, demographic data, and systemic and musculoskeletal comorbidities were determined prospectively for 195 patients with ankle osteoarthritis and ninety-five age and gender-matched controls. The effect of systemic and musculoskeletal comorbidities on each of the scores was determined. Results: On the average, patients with ankle osteoarthritis had a relatively normal MCS score (47 +/- 13 points) and a markedly diminished PCS score (32 +/- 8 points). Both of these scores averaged 50 +/- 9 points in the control group. The AOS pain score averaged 61 +/- 23 points in the group with ankle osteoarthritis, whereas it averaged 10 +/- 15 points in the control group. We found the perception of ankle pain by patients with ankle osteoarthritis to be significantly and linearly associated with the number of other musculoskeletal problems (not related to the foot or ankle). Conclusions: The degree of physical impairment associated with ankle osteoarthritis, as measured with the SF-36, is equivalent to that reported to be associated with severely disabling medical problems including end-stage kidney disease and congestive heart failure. The perception of ankle health status as measured with a validated, patient-oriented, anatomically specific instrument is influenced by the patients' perception of their overall musculoskeletal comorbidity status. The authors of clinical studies using these instruments should adjust for concomitant musculoskeletal disease.