Acetabular retroversion and cam morphology are contributing risk factors for posterior hip dislocation independent of the trauma mechanism.

Introduction: A high-energy trauma impact is generally considered the crucial factor causing native hip dislocation. However, femoroacetabular variations are assumed to contribute to low-energy posterior hip dislocations, especially in adolescent athletes. The study aimed to analyze the femoroacetabular morphology of adults who sustained traumatic posterior hip dislocations, comparing high-energy, sports-related, and low-energy trauma mechanisms.

Materials And Methods: One hundred forty-one patients with traumatic posterior hip dislocations were analyzed and matched to a control group of 141 patients with high-energy trauma mechanisms without hip or pelvic injury, matched for age, gender, and Body Mass Index (BMI). The trauma mechanism was analyzed, and the femoroacetabular morphology and concomitant femoral head or posterior acetabular wall fractures were assessed using computed tomography (CT) scans. Acetabular version, coverage, and pincer morphology were evaluated by measuring the lateral center-edge angle, acetabular index, acetabular depth/width ratio, cranial and central acetabular version angles, and the anterior and posterior acetabular sector angles (AASA, PASA). The caput-collum-diaphyseal (CCD) angle and coronal and axial alpha angles were measured to detect cam morphology.

Results: A high-energy trauma caused posterior hip dislocations in 79.4%, sports-related mechanisms in 7.8%, and a low-energy impact in 12.8%. Patients with high-energy and sports-related dislocations exhibited a higher disposition for acetabular retroversion (p < 0.001). However, the acetabular version in low-energy mechanisms did not differ from the control group (p ≥ 0.05). Acetabular retroversion was associated with isolated dislocation, while acetabular overcoverage correlated with concomitant posterior acetabular wall fractures (p < 0.05). Alpha angles were significantly increased in patients with hip dislocations, independent of the trauma mechanism (p < 0.001).

Conclusion: Acetabular retroversion contributes to posterior hip dislocation in high-energy and sports-related trauma mechanisms and decreases the likelihood of sustaining concomitant fractures. Acetabular morphology was subordinate to causing hip dislocation following a low-energy impact. Increased alpha angles were identified as a risk factor contributing to posterior hip dislocations, regardless of the trauma mechanism.