An audit on the accuracy of freehand acetabular cup positioning in total hip arthroplasty with the direct lateral approach at a tertiary institution over seven years

Abstract

BACKGROUND : The direct lateral approach for total hip replacement has been traditionally reserved and described for neck of femur fractures. Advantages of this approach include technically easy access to the acetabulum and femur and low incidence of hip dislocation. Imperfect positioning of the acetabular component leads to increased risk for dislocations, accelerated wear, reduced range of motion and increased revision rate. Freehand technique has been the gold standard for many decades, but newer technologies like computer navigation and robotic-assisted surgery have shown to improve the accuracy of cup placement. This study reports on the accuracy of freehand cup positioning via the direct lateral approach with mention of the dislocation rate. METHODS : We retrospectively reviewed 253 patients who had total hip replacements done via the direct lateral approach. The patients’ files were evaluated for patient parameters, demographic details, aetiology of hip pathology, confirmation of approach used, comorbidities and history of previous relevant surgery. The postoperative radiographs were analysed for acetabular component position inclination and anteversion. Dislocation rates were calculated as a secondary objective. RESULTS : The radiographic analysis was performed using the Liaw method based on trigonometry of the eclipse generated. This showed a mean cup inclination of 42.3° (95% CI: 41.3–43.3°) and anteversion of 12.7° (95% CI: 12.0–13.7°). A total of 57% of the acetabular cups were within the safe zones described by Lewinnek. Of them, 78% were in the 30–50° range for inclination and 73% in the 5–25° range for anteversion. There were ten dislocations within one year from the index procedure: a dislocation rate of 4.0% (95% CI: 2.8–8.5%). CONCLUSION : The freehand technique using the direct lateral approach for acetabular cup placement produces a poor overall accuracy of only 57%. Although our study only commented on ten dislocations, the rate (4%) is significantly worse compared to the 0.43% reported in literature for the direct lateral approach. The radiographic results for inclination and anteversion are comparable to other freehand techniques, regardless of the approach used, but significantly worse than results achieved with navigation and robotics.