Maximal outcome improvement thresholds after periacetabular osteotomy are approximately 50% on the mHHS and iHOT-12

Maximal outcome improvement (MOI), the percentage of total possible patient-reported outcome measure (PROM) score improvement from baseline, is increasingly being used to describe clinical significance of PROMs. This study defines MOI thresholds for the modified Harris Hip Score (mHHS) and International Hip Outcome Tool-12 (iHOT-12) after periacetabular osteotomy (PAO), determines the proportions of threshold achievement, and identifies the predictors of threshold achievement. We analysed 317 patients who underwent PAO for symptomatic acetabular dysplasia with pre- and postoperative PROMs; postoperative surveys were collected at 1–2 years follow-up. MOI thresholds were calculated with receiver operating characteristic curves. Multivariable logistic regression determined predictors of achieving thresholds using pre- and intraoperative characteristics. MOI thresholds were 47.1% (mHHS) and 50.1% (iHOT-12). Proportions of threshold achievement were 63.1% (mHHS), 61.8% (iHOT-12), and 71.0% (either PROM). Variables with increased risk of failing to achieve thresholds were: mHHS–PAO as revision (OR = 2.51, 95% CI = 1.33–4.76, P < .01), higher preoperative lateral centre-edge angle (OR = 1.06, 95% CI = 1.01–1.12, P = .03), and higher Tönnis grade (OR = 1.90, 95% CI = 1.09–3.30, P = .03); iHOT-12–PAO as revision (OR = 2.30, 95% CI = 1.25–4.26, P < .01), increased body mass index (OR = 1.08, 95% CI = 1.01–1.16, P = .04), and concomitant anterior inferior iliac spine/subspine resection/decompression (OR = 1.81, 95% CI = 1.01–3.26, P = .046). Although newer, MOI provides essential information for contextualizing a patient’s recovery course when used alongside other clinical thresholds.