TP4.6 Identifying Three-Dimensional Acetabular Morphologic Characteristics Associated with Clinical Failure Following Hip Arthroscopy for Femoroacetabular Impingement Syndrome: A Statistical-Shape Modeling Analysis

Abstract

Abstract Background Femoroacetabular impingement syndrome (FAIS) outcomes after hip arthroscopy vary, and osseous morphology of the acetabulum may contribute to clinical failure. While prior work has focused on two-dimensional global measures of acetabular coverage, regional three-dimensional differences in acetabular morphology remain incompletely understood. Methods Patients undergoing hip arthroscopy for FAIS by a single surgeon between 2/2016 and 10/2020 with available preoperative magnetic resonance imaging (MRI) and enrollment in a prospective imaging registry were identified. Patient-reported outcomes (PROs) were collected, and included Hip Outcome Score (HOS) Activities of Daily Living (HOS-ADL), HOS-Sports Specific Subscale (HOS-SS), Modified Harris Hip Score (mHHS), and the 12-Item International Hip Outcome Tool (iHOT-12). Cohort-specific Patient Acceptable Symptom State (PASS) thresholds were determined using the anchor method. Clinical failure was defined as failure to achieve PASS on ≥1 PRO or need for reoperation. Statistical shape modeling (SSM) was performed to compare acetabular morphology between failure and non-failure groups. Results Preoperative MRI scans from 70 patients undergoing hip arthroscopy for FAIS were used to generate three-dimensional acetabular segmentations. Of these, 58 patients (82.9%) had minimum 2-year follow-up and were included in outcome analysis. Thirteen patients (22.4%) met criteria for clinical failure, including 11 who did not achieve PASS and 2 who underwent revision surgery. SSM demonstrated distinct regional differences in acetabular morphology in the failure cohort. Failures exhibited a more prominent posterior acetabular rim (~1.3 mm), a shallower cotyloid fossa (~1.3 mm less depth), and a deeper acetabular notch (~1.6 mm). Collectively, these differences resulted in an approximate 3 mm increase in the distance between the acetabular notch and the posteroinferior rim bordering the notch in the failure group. Conclusions Patients with clinical failure after hip arthroscopy for FAIS demonstrate subtle but consistent differences in acetabular morphology, particularly involving the posterior rim and inferior portion of the acetabulum. Increased posterior rim prominence combined with altered notch and fossa morphology may reflect abnormal posterior-inferior coverage or altered joint mechanics not addressed during standard arthroscopic treatment. These findings highlight the importance of three-dimensional acetabular assessment and may help refine preoperative risk stratification and surgical planning.