Patients With Simple Posterior Hip Dislocations Have Higher Rates of Hip Dysplasia and Borderline Dysplasia.

OBJECTIVES:To determine if patients suffering simple, posterior hip dislocations are more likely to display dysplastic characteristics of their acetabulum as compared with those suffering fracture dislocations. DESIGN:Retrospective cohort study. SETTING:Level 1 trauma center. PATIENTS/PARTICIPANTS:Eighty-six patients suffering posterior, native hip dislocations over a 5-year period. MAIN OUTCOME MEASUREMENT:The primary outcome was measurement of the lateral center edge angle (LCEA), acetabular index (AI), acetabular version, and femoro-epiphyseal acetabular roof (FEAR) index. RESULTS:Eighteen patients (20.9%) sustained simple dislocations, whereas 68 patients (79.1%) suffered fracture dislocations. Patients with simple dislocations had decreased LCEA (25.7 vs. 34.3; P < 0.001), increased AI (7.4 vs. 5.8; P = 0.019), and decreased acetabular anteversion (14.02 vs. 18.45; P = 0.011). Additionally, patients with simple dislocations had higher rates of dysplasia and borderline dysplasia (61.1% vs. 7.3%; P < 0.001). Patients with fracture dislocations had higher rates of concomitant injuries (60.9% vs. 29.4%; P = 0.039) and higher injury severity scores (8.1 vs. 12.3; P = 0.022). CONCLUSION:Patients who sustain simple hip dislocations are more likely to have undercoverage of the femoral head by the acetabulum as compared with patients suffering fracture dislocations. In addition, the simple dislocation group had a lower ISS and fewer concomitant injuries, which likely relates to a lower energy required for dislocation in the setting of lesser bony constraint. Surgeons treating these complicated injuries should consider measurements of LCE and AI when counseling patients on treatment strategies. LEVEL OF EVIDENCE:Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.