Combined Lateral Osseolabral Coverage Is Normal in Hips With Acetabular Dysplasia

Purpose: To compare the lateral osseolabral coverage between groups of patients with different degrees of acetabular bony coverage using a magnetic resonance imaging parameter known as the combined lateral center-edge angle (cLCEA). Methods: The cLCEA was measured among a consecutive series of patients presenting to a dedicated hip preservation surgeon with a magnetic resonance imaging scan. The cLCEA was measured using a coronal T1 or proton density image and was defined as the angle subtended by (1) a line through the center of the femoral head and orthogonal to the transverse line passing through the teardrops of both hips and (2) an oblique line drawn from the center of the femoral head to the free edge of the lateral acetabular labrum. The average difference between the lateral center-edge angle (LCEA) and the cLCEA was calculated and compared between groups based on acetabular bony coverage: dysplasia (LCEA <20 degrees), borderline dysplasia (LCEA 20 degrees-24.9 degrees), normal coverage (LCEA 25 degrees-39.9 degrees), and overcoverage (LCEA >= 40 degrees). Results: In total, 341 patients (386 hips) were included. There were no significant differences in cLCEA between hips with normal acetabular coverage and dysplasia (P = .10) or borderline dysplasia (P = .46). Despite the large difference in mean LCEA between dysplasia (14.8 degrees +/- 3.9 degrees) and acetabular overcoverage (43.1 degrees +/- 2.8 degrees), the mean cLCEA values exhibited only a modest difference (44.7 degrees +/- 4.9 degrees vs 52.7 degrees +/- 4.5 degrees, respectively). Concordantly, hips with dysplasia exhibited the largest difference between mean LCEA and cLCEA (delta = 29.9 degrees +/- 4.7 degrees) and hips with acetabular overcoverage had the smallest difference between measures (9.6 degrees +/- 5.2 degrees). Conclusions: With decreasing acetabular bony coverage, there is increasing labral size such that the total osseolabral coverage, measured by the combined LCEA, remains equivalent between hips with normal acetabular coverage versus dysplasia.