A Specific Anteversion of Cup and Combined Anteversion for Total Hip Arthroplasty Using Lateral Approach

OBJECTIVE: To determine the implant orientation, especially the combined anteversion measurements in total hip arthroplasty (THA) using lateral approach, and to compare with implant orientation using posterior‐lateral (P‐L) approach. The secondary goal was to identify the factors associated with implant orientation. METHODS: Five hundred and one patients (545 hips) who underwent primary THA with the modified Hardinge approach between January 2016 and November 2019 by one senior surgeon in our department in a retrospective study were followed up. A survey to inquire about the history of dislocation of the hip after THA was designed and responses were gathered by telephone, WeChat software, and outpatient follow‐up. The mean age of the patients was 61.97 ± 11.72 years, and there were 254 males and 247 females. The average follow‐up time was 25.2 ± 13.7 months (range, 3.2–49.7 months). Among the patients who were followed up, 97 patients (104 hips) underwent computed tomography (CT) scans from L(4) to the tuberosity of the tibia. The implant orientation, including the anteversion and inclination of the cup, anteversion of the stem, combined anteversion, and pelvic tilt were measured based on CT scans of these patients. The results were compared with the implant orientation reported in previous reports measured by CT. Factors that may be associated with implant orientation were investigated, including the patient's age, sex, body mass index (BMI), and diagnosis; size of the cup; diameter of the femoral head component; and pelvic tilt. Data and statistical analyses were performed using SPSS 20.0. RESULTS: No cases of dislocation were found in the 501 patients (545 hips) who underwent primary THA during this period. The mean inclination and anteversion of the cups were 38.83° ± 5.04° (24.5°–53.1°) and 9.26° ± 11.19° (−15°–48°), respectively. The mean anteversion of the stem was 13.83° ± 10.7° (−10.2°–42.3°). The combined anteversion was 23.1° ± 13.4° (−7.4°–54.6°). Compared with the reported combined anteversion and anteversion of the cup, the mean anteversion of the cup and combined anteversion using the lateral approach were much lower than the reported values in the literature using the P‐L approach. Pelvic tilt was found to be the only independent factor for cup anteversion. Factors including age, sex, BMI, diagnosis, cup size, and diameter of the femoral head component were not associated with implant orientation. CONCLUSION: THA using the lateral approach yields smaller cup anteversion and combined anteversion values than using the P‐L approach. Pelvic tilt is the only predictor for cup anteversion.