EP1.50 A Series of Studies on Factors Associated with Capsular Repair and Clinical Outcomes in Borderline Developmental Dysplasia of the Hip

Abstract Purpose This series of studies aimed to comprehensively investigate capsular characteristics in patients with borderline developmental dysplasia of the hip (BDDH) and femoroacetabular impingement syndrome (FAIS). Specifically, we evaluated anterior capsular integrity and thickness on MRI, explored their associations with femoral version and neck–shaft angle (NSA), and examined their relationship with postoperative clinical outcomes. Methods Four retrospective analyses were conducted. (1) In BDDH patients undergoing hip arthroscopy (2018–2020) with ≥2-year follow-up MRI, patients were grouped based on postoperative capsular healing status (healed vs. unhealed/partially healed). Patient-reported outcomes (PROs) were compared. (2) In FAIS patients (Nov 2021–Jul 2022), femoral version was measured by CT and anterior capsular thickness (ACT) by MRI. Multivariable linear regression and propensity score matching were applied. (3) In FAIS patients (Jan–Jul 2022), the relationship between NSA (CT) and ACT (MRI) was analyzed using multivariable regression. (4) In BDDH patients (2016–2019), outcomes of capsular repair versus non-repair were compared. Capsular integrity and thickness were assessed by MRI with ≥1-year follow-up, and propensity score matching was used to control confounders. Results (1) Among 59 BDDH patients, 93.2% of repaired capsules remained closed. After matching (n=25 per group), the unhealed/partially healed group demonstrated significantly thinner ACT (3.0±1.2 mm vs. 4.1±0.6 mm, P<0.001) and inferior PROs (HOS-ADL, HOS-SSS, iHOT-12), with lower rates of achieving MCID and PASS. (2) In 156 FAIS patients, femoral version (P<0.001) and sex (P=0.002) were independently associated with ACT; each 1° increase in femoral version corresponded to a 0.35 mm decrease in ACT. (3) In 150 FAIS patients, NSA (P=0.002) and sex (P=0.001) were negatively correlated with ACT; each 1° decrease in NSA corresponded to a 0.24 mm increase in ACT. (4) In BDDH patients (n=74), the non-repair group showed a higher rate of critical capsular defects (27.0% vs. 8.1%, P=0.032) and significantly thinner ACT (2.9±0.5 mm vs. 3.7±0.6 mm, P<0.001), while no significant thinning was observed in the repair group. Conclusion Incomplete capsular healing in BDDH is associated with inferior clinical outcomes, and anterior capsular thickness may serve as a prognostic indicator. ACT is significantly associated with femoral version and NSA, providing insight into individualized capsular management strategies. Routine capsular repair in BDDH improves healing rates and preserves capsular thickness, whereas non-repair leads to thinning and higher defect rates. These findings highlight the critical role of the hip capsule in both BDDH and FAIS and support its importance in surgical decision-making.