FP1.3 Borderline Developmental Dysplasia of the Hip With Osseous Impingement as Distinct From Femoroacetabular Impingement and Developmental Dysplasia of the Hip

Background: Borderline developmental dysplasia of the hip (BDDH) accompanied by cam deformity and subspinous impingement has been found to benefit from arthroscopic surgery. However, the research comparing BDDH combined with osseous impingement to femoroacetabular impingement (FAI) without borderline dysplasia remains limited.

Purpose: To compare the clinical symptoms, intraoperative findings, and outcomes of hip arthroscopic surgery in patients with BDDH and osseous impingement versus cam-type FAI. We hypothesized that BDDH with osseous impingement could be classified as a distinct entity between FAI and developmental dysplasia of the hip (DDH).

Methods: Data were retrospectively collected from patients aged 18 to 50 years who underwent primary hip arthroscopy between September 2016 and October 2020. Patients were divided based on preoperative lateral center-edge angle (LCEA) into 2 groups: (1) BDDH group (LCEA18°-25°; n = 67) and (2) cam-type FAI group without BDDH (LCEA 25°-40°and alpha angle >55°; n = 145). Disparities in symptoms, preoperative examination, and intraoperative findings and procedures, and patient-reported outcome scores (PROs) were compared.

Results: Follow-up was available for 61(91.0%) patients in the BDDH group 125(86.2%) patients in the FAI group. The incidence of cam deformity in BDDH patients was 91.8%. The preoperative characteristics and intraoperative findings were similar between the groups, however, preoperative internal and external hip rotation, Tönnis angle, femoro-epiphyseal acetabular roof index, labral size, capsule thickness, and percentage of ligamentum teres tear were significantly higher in the BDDH versus the FAI group, and the percentage of pain aggravating factor, cam deformity and anterior inferior iliac spine types 2 and 3 between groups were also significantly different (P<.05 for all). The percentage of intraoperative minimal acetabuloplasty, subspinous decompression, labral repair, ligamentum teres debridement, and capsular closure were significantly higher in the BDDH versus the FAI group, while the percentage of femoroplasty was higher in the FAI group (P<.05). Pre-to postoperative improvement on PRO scores was seen in both groups.

Conclusion: Given the differences in etiology and surgical procedures between the two conditions, it is suggested that BDDH with osseous impingement be classified as an entity distinct from FAI and DDH (and separate from BDDH without impingement), while excluding joint instability.