Validation of the Mayo Hip Score: construct validity, reliability and responsiveness to change

BACKGROUND Previous studies have provided the initial evidence for construct validity and test-retest reliability of the Mayo Hip Score. Instruments used for Total Hip Arthroplasty (THA) outcomes assessment should be valid, reliable and responsive to change. Our main objective was to examine the responsiveness to change, association with subsequent revision and the construct validity of the Mayo hip score. METHODS Discriminant ability was assessed by calculating effect size (ES), standardized response mean (SRM) and Guyatt's responsiveness index (GRI). Minimal clinically important difference (MCII) and moderate improvement thresholds were calculated. We assessed construct validity by examining association of scores with preoperative patient characteristics and correlation with Harris hip score, and assessed association of scores with the risk of subsequent revision. RESULTS Five thousand three hundred seven provided baseline data; of those with baseline data, 2,278 and 2,089 (39%) provided 2- and 5-year data, respectively. Large ES, SRM and GRI ranging 2.66-2.78, 2.42-2.61 and 1.67-1.88 were noted for Mayo hip scores with THA, respectively. The MCII and moderate improvement thresholds were 22.4-22.7 and 39.4-40.5 respectively. Hazard ratios of revision surgery were higher with lower final score or less improvement in Mayo hip score at 2-years and borderline significant/non-significant at 5-years, respectively: (1) score ≤55 with hazard ratios of 2.24 (95% CI, 1.45, 3.46; p = 0.0003) and 1.70 (95% CI, 1.00, 2.92; p = 0.05) of implant revision subsequently, compared to 72-80 points; (2) no improvement or worsening score with hazard ratios 3.94 (95% CI, 1.50, 10.30; p = 0.005) and 2.72 (95% CI, 0.85,8.70; p = 0.09), compared to improvement >50-points. Mayo hip score had significant positive correlation with younger age, male gender, lower BMI, lower ASA class and lower Deyo-Charlson index (p ≤ 0.003 for each) and with Harris hip scores (p < 0.001). CONCLUSIONS Mayo Hip Score is valid, sensitive to change and associated with future risk of revision surgery in patients with primary THA.