A Core Outcome Measures Index (COMI) for patients undergoing hip arthroplasty.

Outcome is best assessed with both generic and disease-specific instruments, but using many, lengthy questionnaires increases the burden, quality, and cost of data collection.We evaluated a short, hip-oriented Core Outcome Measures Index (COMI-hip), comprising six items (pain, function, symptom-specific well-being, quality of life, and disability) extracted from established full-length questionnaires; 214 consecutive total hip arthroplasty (THA) patients participated. Scores for the single items and sum-score of COMI-hip correlated well with those of the full-length instruments (r= -0.56 to -0.88). At 6 and 12 months' follow-up, the COMI-hip showed similar responsiveness (Cohen's d for effect size, 1.36-3.08) to the full-length questionnaires (1.65-2.34). The COMI-hip proved a simple but valid outcome instrument in THA patients. Its brevity renders it a potentially valuable instrument for routine use.