What Factors Increase the Risk of Dislocation after Primary Total Hip Arthroplasty Using the Direct Anterior Approach?

Abstract

While the direct anterior approach (DAA) for total hip arthroplasty (THA) is associated with a lower risk of dislocation, this complication has not been eliminated and can be acutely disabling when it occurs. This study aimed to identify patient, surgical, and radiographic factors that contribute to dislocation risk for the DAA based on primary THAs performed over a 15-year period. Using an institutional database, we identified 8,658 DAA THAs performed by four surgeons from March 2009 through May 2024. A Cox proportional hazards regression was performed to determine how patient demographics and implant characteristics were associated with dislocation. Patients who dislocated were also compared to a matched control cohort without dislocation to evaluate the influence of radiographic parameters, including acetabular cup orientation, offset, limb length changes, and preoperative acetabular coverage. The dislocation rate among all primary THAs was 0.5% (45 of 8,656). Women had a higher dislocation rate than men (0.7 versus 0.2%), and Cox regression identified an increased risk among women with 28 mm (hazard ratio (HR) 7.5; 95% confidence interval (CI) 3.2 to 17.6) and 32 mm heads (HR 3.8; 95% CI 1.9 to 7.5). Radiographic analysis showed no significant differences in total offset (P = 0.13) or limb length change (P = 0.41), but controls demonstrated significantly lower variance in cup inclination (P = 0.01). Although the incidence of dislocation after THA using the DAA is low, women who have smaller diameter femoral heads are at increased risk of dislocation. The significantly lower variance in radiographic inclination among controls also underscores the importance of precise cup positioning.