Validation of the Core Outcome Measures Index in Patients With Femoroacetabular Impingement

Abstract

To evaluate a short, hip-oriented outcome instrument, based on the Core Outcome Measures Index (COMI), in patients undergoing surgery for femoroacetabular impingement (FAI). The following full-length questionnaires were completed preoperatively and at 6 and 12 months postoperatively by 159 consecutive FAI patients: Hip Outcome Score (HOS); Oxford Hip Score; Western Ontario and McMaster Universities Arthritis Index; Short Form 12 Health Survey; World Health Organization Quality of Life questionnaire, short version; and EuroQol-Five Dimensional index. The scores for the 6 hip-oriented Core Outcome Measures Index (COMI-Hip) items-addressing pain, function, symptom-specific well-being, quality of life, and disability-were extracted from established full-length questionnaires, and their performance as an index was compared with that of the full-length instruments. Scores for the single items of the COMI-Hip questionnaire correlated well with the scores for the corresponding full-length instruments from which they were extracted (r=-0.89 to-0.62, P < .001). The COMI-Hip sum score also correlated well with the Oxford Hip Score and the Western Ontario and McMaster Universities Arthritis Index pain and function scores (r=-0.85 to-0.70, P < .001), as well as with the HOS (r=-0.72 to-0.60, P < .001), an instrument specifically developed for assessing FAI patients. Internal responsiveness (Cohen d for effect size) of the COMI-Hip sum score from preoperatively to 12 months postoperatively was similar to that of the HOS activities-of-daily living subscale (d=-0.76 and d=-0.68, respectively; P < .001). Significant correlations were found between the change scores of the COMI-Hip sum score and those of the HOS activities-of-daily living and sport subscales at 6 months (r=-0.62 and r=-0.60, respectively; P < .001) and 12 months (r=-0.69 and r=-0.61, respectively; P < .001), showing the external responsiveness of the COMI-Hip. The COMI-Hip is a simple yet valid and responsive outcome instrument for the efficient assessment of patients undergoing surgery for FAI. It performs at least as well as the current reference instrument for FAI, the HOS, and can therefore be considered a potentially valuable instrument for routine use in both research and clinical practice. Level II, development of diagnostic criteria based on consecutive patients (with universally applied reference gold standard).