Paper 40: Predictors of surgical treatment in borderline acetabular dysplasia: results from the multicenter anchor orbit study

Objectives: Borderline acetabular dysplasia, defined by a lateral center-edge angle (LCEA) between 18-25°, remains a major controversy in hip preservation surgery. Both isolated hip arthroscopy and periacetabular osteotomy (PAO) appear to be the optimal treatment for distinct subgroups of patients, but limited information guides this decision-making. A multicenter prospective cohort study can provide data to guide surgical decision-making in the borderline population. The study's primary objective is to identify demographic, clinical, and radiographic predictors of significant instability requiring treatment with a PAO (with or without arthroscopy), instead of isolated hip arthroscopy, in patients with borderline acetabular dysplasia.
Methods: The ANCHOR ORBIT study is a multicenter prospective cohort involving 30 surgeons at 23 institutions. A total of 541 patients undergoing primary hip surgery with LCEA 18-25° were included. Treatment groups were defined as (1) isolated arthroscopy and (2) PAO (with or without arthroscopy). Treatment decision-making was at the discretion of the treating surgeon based on comprehensive assessment. Multivariable logistic regression identified independent predictors of treatment selection.
Results: A total of 541 patients met inclusion (mean age 24.3 +- 7.9 years; 75.2% female), including 284 patients (52.5%) treated with isolated hip arthroscopy and 257 patients (47.5%) treated with PAO, of whom 119 (22.0%) underwent PAO alone and 138 (25.5%) underwent PAO with arthroscopy. The presence of significant instability driving the decision for PAO was independently associated with: smaller LCEA (OR 0.54, 95% CI 0.46-0.62, p<0.001), higher Beighton score (OR 1.15, 95% CI 1.01-1.31, p=0.038), increased internal rotation at 90° flexion (OR 1.06 per degree, 95% CI 1.03-1.10, p<0.001), lower alpha angle (OR 0.96 per degree, 95% CI 0.94-0.98, p<0.001), and younger age (OR 0.96 per year, 95% CI 0.92-1.01, p=0.09,). The final model demonstrated strong explanatory power (Nagelkerke R²=0.68).
Conclusions: In this large multicenter cohort, surgical treatment for borderline acetabular dysplasia was nearly evenly divided between isolated arthroscopy and PAO (with or without arthroscopy). Clinical and radiographic factors strongly influenced treatment choice: LCEA, hip internal rotation, alpha angle, age, and ligamentous laxity independently predicted PAO. These findings provide multicenter evidence that both structural and patient-specific factors drive surgical decision-making in this controversial population.