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Paper 09. 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
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Paper 09. 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

Jeffrey J. Nepple, Abhav Garde, Robert W. Westermann, Andrea M. Spiker, Christopher M. Larson, Yi-Meng D. Yen, Young-Jo Kim, John C. Clohisy and ANCHOR Study Group
Orthopaedic journal of sports medicine, Vol.14(8_suppl6)
08/01/2026
DOI: 10.1177/2325967126S00270
PMCID: PMC13530609
url
https://doi.org/10.1177/2325967126S00270View
Published (Version of record) Open Access

Abstract

Objectives: Borderline acetabular dysplasia (BD) is a common young adult hip disorder with limited evidence to guide diagnosis and surgical decision-making between isolated hip arthroscopy (HA) or periacetabular osteotomy (PA). BD is present in up to 30% of patients undergoing isolated hip arthroscopy and is a risk factor for inferior outcome. 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) using the Borderline Hip Instability Score (BHIS) to stratify patients by relative instability. Methods: A prospective multicenter cohort study was performed of the primary surgical treatment of BD. The cohort included 541 patients with lateral center edge angle (LCEA) 18°-25° treated across 30 surgeons at 23 high volume hip preservation centers. Primary outcome metrics for baseline and follow-up included a PRO dataset consisting of 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, maximum 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% (n=284) underwent HA and 47.5% (n=257) underwent PAO. Mean age at surgery was 24.7 years (range 14-45) with 75.2% being female. Minimum six-month follow-up (range 5-11 months) 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 more unstable group, 46.7% underwent PAO while 53.3% underwent HA. In the more stable group, 24.6% underwent PAO while 75.4% underwent HA. 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). Additionally, 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), while HOOS pain showed non-significant higher scores (less pain) in the HA group compared to PAO (87.0 ± 12.3 vs 82.3 ± 17.5, p = 0.057). Conclusions: 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. Future research will follow this established cohort at more important long-term timepoints.

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