Responsiveness and ceiling effects of the English version of the 12-item International Hip Outcome Tool following hip arthroscopy at minimum one-year follow-up

Aims: Responsiveness and ceiling effects are key properties of an outcome score. No such data have been reported for the original English version of the International Hip Outcome Tool 12 (iHOT-12) at a follow- up of more than four months. The aim of this study was to identify the responsiveness and ceiling effects of the English version iHOT-12 in a series of patient sundergoing hip arthroscopy for intra- articular hip pathology at a minimum of one year postoperatively. Methods: A total of 171 consecutive patients undergoing hip arthroscopy with a diagnosis of femoroacetabular impingement(FAI) under the care of a single surgeon between January 2013 and March 2017were included. iHOT-12 and EuroQol 5D- 5L (EQ- 5D- 5L) scores were available pre- and postoperatively. Effect size and ceiling effects for the iHOT-12 were calculated with subgroup analysis. Results: A total of 122 patients (71.3%)completed postoperative PROMs scores with median follow- up of 24.3 months(interquartile range (IQR) 17.2 to 33.5). The median total cohort iHOT-12 score improved significantly from 31.0 (IQR 20 to 58) preoperatively to 72.5 (IQR 47to 90) postoperatively (p < 0.001). The effect size (Cohen’s d) was 1.59. In all, 33 patients (27%) scored within ten points (10%) of the maximum score and38 patients (31.1%) scored within the previously reported minimal clinically important difference (MCID) of the maximum score. Furthermore, nine (47%) male patients aged < 30 years scored within 10% of the maximum score and ten(53%) scored within the previously reported MCID of the maximum score. Conclusion: There is a previously unreported ceiling effect of the iHOT-12 at a minimum one-year follow- up which is particularly marked in young, male patients following hip arthroscopy for FAI. This tool may not have the maximum measurement required to capture the true outcome following this procedure.