EP8.15 Increasing BMI associated with poorer predicted post-operative patient-reported outcome measures following peri-acetabular osteotomy for developmental dysplasia of the hip – A national registry study

Abstract Introduction This study aimed to assess the impact of body mass index (BMI) on post-operative patient-reported outcome measures (PROMs) from periacetabular osteotomy (PAO) for developmental dysplasia of the hip (DDH). Materials and Methods All PAO performed for DDH were identified in the UK Non-Arthroplasty Hip Registry (NAHR) between January 2012 and November 2025. PROMs utilised were iHOT-12, EQ-5D Visual Analogue Scale (VAS) and EQ-5D Index. Multiple linear regression (MLR) and ANOVA, as well as Tukey’s Highly Significant Difference (HSD) were used to assess trends in absolute PROM score and score improvement from baseline on a continuous and categorical basis, utilising World Health Organisation (WHO) BMI categories. Results 718 PAO with BMI data were identified. The majority of patients were either “Healthy” (53.8%, n=386) or “Overweight” (27.7%, n=199) BMI categories. Obese Class III (BMI ≥40) patients were excluded due to low numbers (n=3). Increasing BMI was associated with poorer predicted absolute iHOT-12 score at 12 months post-operatively (-0.65 [SE 0.27], p=0.0174) and a non-significant trend towards poorer predicted outcomes was noted at 12-months for EQ-5D VAS (-(-0.31 [SE 0.18], p=0.0883) and EQ-5D Index (-0.0040 [SE 0.0024], p=0.0939). ANOVA demonstrated a significant association between BMI and absolute outcome at 12-months post-operatively for iHOT-12 (p<0.0001), EQ-5D VAS (p=0.0182) and EQ-5D Index (p=0.0003) as well as at 6-months post-operatively for EQ-5D Index (p=0.0205). ANOVA for WHO BMI category showed a statistically-significant association between BMI and iHOT-12 (p=0.0017), EQ-5D VAS (p=0.001765) and EQ-5D Index (p=0.0020) at 12-months post-operatively. Increasing BMI was associated with greater predicted EQ-5D Index 0.0058 [SE 0.0025], p=0.0216), score improvement from baseline at 6 months post-operatively. ANOVA for effect of WHO BMI category on outcomes was significant for EQ-5D VAS (p=0.01623) and EQ-5D Index (p = 0.0499) at 6 months. Conclusions This study demonstrates a modest, statistically-significant association between increasing BMI and poorer iHOT-12 scores at 12 months post-operatively, as well as trends towards poorer iHOT-12 scores at 12 months for EQ-5D VAS and EQ-5D Index. Patients with increased BMI demonstrated greater PROM score improvement at 6 months post-operatively compared to Healthy weight patients, but these improvements were lost by 12 months.