Understanding a Rare Injury: An Observational Study of Anterior-Superior Hip Dislocations.

OBJECTIVE. The goals of this study were to assess the prevalence of anterior hip dislocation and to highlight the distinctive imaging features of anterior-superior hip dislocation. MATERIALS AND METHODS. A retrospective chart review was conducted of all hip dislocations seen at one university hospital from January 2005 to January 2019. The radiology database was queried for all reports of hip or pelvis radiographs with the word "dislocation." Cases of developmental dysplasia of the hip, infection, tumor, arthroplasty, Girdlestone procedure, surgical dislocation, and prior hip surgery were excluded, leaving 237 traumatic hip dislocations. Electronic medical records of the 18 cases of anterior hip dislocation were reviewed to determine the mechanism of injury, treatment, and subsequent outcomes. RESULTS. Among 237 traumatic hip dislocations, 18 (7.6%) were anterior hip dislocations. Among the 18 were three (17%) anterior-superior dislocations and 15 (83%) anterior-inferior dislocations. All anterior-superior dislocations had poor outcomes. One patient had persistent hip pain and instability and underwent follow-up imaging. In one case, MRI performed at the time of injury and 11 months later showed tears of the superior capsule, iliofemoral ligament, and ligamentum teres. The iliofemoral ligament tear did not heal, resulting in a persistent anterior capsule defect, a finding previously associated with instability in patients who have undergone arthroscopic surgery. CONCLUSION. The incidence of anterior hip dislocation was lower than some studies have suggested. Anterior-superior hip dislocation is a rare injury in which ligamentous defects are visualized at MRI and possibly contribute to anterior hip instability and pain.