Introduction STAR total hip arthroplasty (THA) approach preserves piriformis whilst providing sufficient visualization of the acetabulum, potentially comparable to technology-assisted systems. This multicenter study compared acetabular cup positioning within the Lewinnek safe zone between manual and technology-enabled STAR cohorts. We hypothesized comparable accuracy between methods, suggesting that the preservation of the piriformis does not obstruct the optimal access to the acetabulum in the manual STAR THA. Methods A total of 772 primary STAR THAs from two institutions were analyzed. Patients were matched 1:1 for age, sex, BMI, ASA class, and operative side, resulting in 386 manual and 386 technology-enabled cases. Technology-enabled THA included both computer-assisted and robotic systems. Cup inclination and anteversion were measured on postoperative supine anteroposterior pelvic radiographs using the Widmer method. A subset of 20 radiographs independently reviewed by an external observer, demonstrated excellent inter-observer reliability. Cup positioning was evaluated based on compliance with the Lewinnek safe zone criteria (inclination 30°–50°, anteversion 5°–25°). Groups were compared using two-sample proportion tests with significance set at p < 0.05. Results Groups were well matched across baseline variables (standardized mean differences < 0.10). Mean cup inclination was 42.8° ± 4.9° in the manual group and 44.3° ± 3.7° in the technology-enabled group. Mean anteversion was 20.1° ± 7.7° and 23.6° ± 5.4°, respectively. 65 % of manual and 68.4% of technology-enabled THAs were within the Lewinnek safe zone (absolute difference 3.4%, p = 0.36, 95% CI −10.3% to 3.5%). No significant differences in cup orientation or distribution were observed. Conclusion THA performed via the manual STAR approach, did not significantly differ by the technology-enabled systems with regards of the acetabular component positioning within the Lewinnek safe zone. These findings indicate that the STAR approach itself provides reliable and reproducible visualization, enabling precise cup placement, while preserving the piriformis.
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