Acetabular morphology predicts the risk of dislocation following hemiarthroplasty for femoral neck fractures in the elderly

Background: Hip hemiarthroplasty dislocation is a devastating complication. Among other preoperative risk factors, acetabular morphology has been rarely studied. The purpose of the study was to evaluate the influence of preoperative native acetabular morphology on hemiarthroplasty dislocation. Material and methods: We retrospectively reviewed 867 patients who underwent hip hemiarthroplasty for femoral neck fracture between January 1, 2014 and January 1, 2019. The 380 patients were treated with an anterior-based muscle-sparing approach. Central-Edge Angle (CEA) and Acetabular Depth-to-Width Ratio (ADWR) of the fractured hip were measured pre-operatively on the antero-posterior (AP) pelvic view. Receiver Operating Characteristic (ROC) curves were performed to analyze the optimal cut-off for CEA and ADWR. Hemiarthroplasty dislocation occurred in 18 patients (4.7%) and the remaining 362 were used as the control group. Results: No significant differences in terms of sex, age, dementia, neuromuscular disease, and body mass index (BMI) were found between the 2 groups. The 18 patients who had a hip dislocation had significantly smaller mean CEA than the control group (p=0.0001) (mean 36.1±7.5° and 43.2±5.6°, respectively) as well as ADWR (mean 34±6 vs 37±4, respectively) (p=0.001). Using the ROC analysis, we report significant cut-offs of 38.5° for CEA (p=0.0001) and 34.5 for the ADWR (p=0.017). Conclusions: Higher rates of hemiarthroplasty dislocation were observed in patients who had a preoperative CEA of less than 38.5° and an ADWR of less than 34.5. Patients who have preoperative acetabular morphological risk factors for dislocation might be better candidates for a total hip arthroplasty.