Dysplastic Hips Have Decreased Iliofemoral Ligament Thickness on Coronal Sequences in Magnetic Resonance Imaging: A Matched Cohort Analysis.

ABSTRACT

PURPOSE: To characterize hip capsule thickness on advanced imaging in patients with and without hip dysplasia and to also evaluate differences in capsular thickness between patients with borderline and patients with true dysplasia. METHODS: Patients evaluated by the senior author for concerns of hip pathology from June 2020 to June 2021 were queried and images reviewed to determine dysplasia status by lateral center-edge angle (LCEA) ≤25°. A group of patients without dysplasia was identified and matched for age, sex, and body mass index. Hip capsular thickness was quantified using magnetic resonance imaging. A subanalysis was conducted to compare patients with true dysplasia (LCEA < 20°) with patients with borderline dysplasia (LCEAs between 20° and 25°). The analysis included independent samples t tests, χ2 tests, and multivariable regression. RESULTS: A total of eighty patients were included, with a mean age of 31.8 ± 11.7 years, a mean body mass index of 26.6 ± 6.5 points, and 70% (56) female patients. Patients with dysplasia had a mean LCEA of 19.8 ± 4.3°. Patients with dysplasia had decreased capsular thickness compared with patients without dysplasia (2.75 ± 0.96 mm vs 3.52 ± 1.22 mm, P = .003). Multivariable regression showed decreased capsular thickness associated with decreased LCEAs (ß = 2.804, R = 0.432, P < .001) and dysplasia (ß = -0.709, R2 = 0.056, P = .004). Results of a subanalysis of the dysplastic group examining differences between accepted definitions of borderline dysplasia and true dysplasia showed no significant differences in capsular thickness between the 2 groups (P = .379). CONCLUSIONS: Patients with hip dysplasia were found to have thinner iliofemoral ligaments in the coronal plane on magnetic resonance imaging on magnetic resonance imaging. Further investigation is needed to evaluate any potential implications with hip instability, given the thinner hip capsule demonstrated in this study. LEVEL OF EVIDENCE Level III, retrospective comparative prognostic trial.