Lateral Acetabular Coverage Predicts the Size of the Hip Labrum

Abstract

Background: Bony morphological abnormalities of the hip joint are often accompanied by adaptive soft tissue changes. These adaptive changes, if better understood and characterized, may serve to inform clinical decision making. Purpose: To investigate the correlation between the size of the hip labrum and lateral acetabular coverage in patients at our hip preservation clinic. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A cohort of 236 patients seen at a dedicated hip preservation service between June 2013 and June 2015 were retrospectively analyzed. Patients were grouped according to the degree of acetabular coverage, as measured by the lateral center-edge angle (LCEA): normal acetabular coverage (25°-39.9°), acetabular overcoverage (≥40°), borderline dysplasia (20°-24.9°), and frank dysplasia (<20°). Preoperative magnetic resonance imaging was utilized to measure the length of the labrum at 3 locations: laterally, anteriorly, and anteroinferiorly. Results: Frankly dysplastic and borderline dysplastic hips exhibited larger values of labral length at all locations when compared with hips with normal acetabular coverage ( P < .001) or acetabular overcoverage ( P < .001). Interestingly, mean labral length values in frank dysplasia were statistically similar to corresponding measurements in borderline dysplasia. In hips with frank dysplasia, borderline dysplasia, or normal acetabular coverage, labral length was consistently greatest at the lateral labrum and correspondingly lowest at the anteroinferior labrum ( P < .001). In hips with acetabular overcoverage, labral length did not vary significantly between the lateral, anterior, and anteroinferior locations. Multivariate analyses confirmed LCEA to be the strongest predictor of labral length, irrespective of measurement location. Conclusion: Patients with borderline dysplasia and frank dysplasia exhibited increased values of labral length in the weightbearing zone, potentially indicating a compensatory reaction to the lack of bony coverage. Labral length may serve as an instability marker and inform clinical decision making for patients with borderline dysplasia.