Hip Alpha Angle is Associated with Anterior-Superior Labral Tears but not Anterior Labral Tears.

INTRODUCTION: The purpose of this study is to examine the associations between hip and acetabular morphology, clinical and demographic patient factors, and acetabular labral tear location in young adults.

MATERIALS AND METHODS: This study was reviewed by the local Institutional Review Board. The hip magnetic resonance imaging arthrograms from 100 young adult patients (aged 18-35 years) who underwent hip arthroscopy within 1 month of the arthrogram were reviewed. Clinical and demographic variables including age, height, weight, body mass index (BMI) and quantitative hip measurements of acetabular anteversion, alpha and beta angles, femoral head extrusion index, lateral center edge angle, acetabular depth-width ratio, Sharp's and Tönnis' angles were measured, and compared based on acetabular tear location.

RESULTS: Ninety-six (96%) of patients had arthroscopically confirmed acetabular tears, and 4 (4%) patients had a normal acetabula labrum. Most (85 [88.5%]) patients had tears involving the anterior-superior labrum and another location, 41 (42.7%) patients had tears involving the anterior labrum and another location, and 35 (36.5%) had tears involving the superior-lateral labrum and another location. Tears commonly occurred in more than one location, with 37 (38.5%) patients having tears in both the anterior and anterior-superior labrum; 28 (29.2%) patients with tears in both the anterior-superior and superior-lateral labrum and 11 (11.5%) patients with tears in the anterior and superior-lateral labrum. Patients with isolated tears of the anterior-superior labrum had on average higher alpha angles than patients with isolated tears of the anterior labrum (P = 0.007). In patients with anterior-superior labral tears, increased BMI (P = 0.033), and weight (P = 0.024) were associated with having concomitant tears of the superior-lateral labrum.

DISCUSSION: MR arthrograms are 96% sensitive for detecting acetabular labral tears. Acetabular labral tears tend to co-occur in different locations, with anterior and anterior-superior labral tears most commonly co-occurring. Patients with isolated anterior-superior labral tears had on average higher alpha angles than patients with isolated anterior labral tears.