TP1.7 Short-Term Outcomes of Treatment of Borderline Acetabular Dysplasia Differ Relative to Amount of Instability: A Multicenter ANCHOR ORBIT Study Comparing Hip Arthroscopy and Periacetabular Osteotomy

Abstract

Abstract Introduction Limited evidence exists to guide surgical decision-making in borderline acetabular dysplasia (BD) between isolated hip arthroscopy (HA) or periacetabular osteotomy (PAO). The purpose of this study was to compare short-term outcomes (minimum 6 months) of BD treated with (1) isolated HA or (2) PAO (with or without arthroscopy) including stratification by relative instability. Methods A prospective multicenter cohort study was performed of the primary surgical treatment of BD. The cohort included 541 hips with lateral center edge angle (LCEA) 18°-25° treated across 30 surgeons. PROs utilized included HOOS pain, HOOS sports, mHHS, and iHOT-12, assessed at baseline through six-month follow-up. The BHIS was previously developed and validated to quantify key patient factors driving treatment decisions and includes relative weighting of the following clinical and radiographic parameters (mean 50, range 0-100): acetabular inclination, anterior center-edge angle, alpha angle, and internal rotation at 90° flexion. Outcomes were stratified by BHIS scores of <50 (more stable hips) and >50 (more unstable hips), as well as >60 (highly unstable). Results The cohort included 541 hips of which 52.5% underwent HA and 47.5% underwent PAO. Minimum six-month follow-up was available in 80.1% of hips. The BHIS subgroups included BHIS>50 (more unstable) in 50.2% and BHIS<50 in 49.8%. In the unstable subgroup, there was a non-significant trend towards greater improvement in HOOS pain (less pain) in the PAO group than the HA group at 6 months (28.0 ± 19.7 vs 22.2 ± 22.1, p = 0.07). In highly unstable hips (BHIS > 60), improvement in HOOS pain from baseline was significantly higher (less pain) in the PAO group than the HA group at 6 months (30.8 ± 20.8 vs 25.0 ± 14.6, p = 0.027). In the more stable subgroup, HOOS sports scores were significantly higher with HA compared to PAO (81.3 ± 18.7 vs 73.9 ± 22.9, p = 0.039). Conclusion Subgroups of patients with BD can be treated effectively with both HA and PAO depending on severity of instability. At minimum 6-month follow-up, PAO demonstrates improved outcomes for highly unstable borderline hips while HA demonstrates superior early outcomes for more stable borderline hips.