A Prospective Study on Acetabular Cup Positioning Using Anatomical Landmarks in Primary Total Hip Arthroplasty at a Tertiary Care Center in Mumbai

Background: Accurate acetabular cup positioning in total hip arthroplasty (THA) reduces complications such as dislocation and wear. While the Lewinnek safe zone guides placement, freehand methods vary. Anatomical landmarks like the transverse acetabular ligament offer a cost-effective alternative. This study evaluated their accuracy and early outcomes at a Mumbai tertiary center. Material and Methods: This prospective observational study included 50 patients (52 hips) undergoing primary uncemented total hip arthroplasty at a tertiary care hospital in Mumbai over one year. All surgeries were performed by a single experienced surgeon using a posterolateral approach, with acetabular cup placement guided by anatomical landmarks. Intraoperative stability and range of motion were assessed. Postoperative evaluation used standardized anteroposterior pelvic radiographs, with CT scans when required, to measure inclination and anteversion using the modified Murray method. Ethical approval and informed consent were obtained. Data were analyzed descriptively, with outliers defined beyond the Lewinnek safe zone, and functional outcomes assessed using Harris Hip Score at follow-up. Results: The mean radiographic inclination was 41.2° ± 4.8° (range 32°–52°), and mean anteversion was 16.8° ± 5.2° (range 6°–28°). Overall, 88% of cups (46/52) fell within the Lewinnek safe zone for both parameters, with 94% within safe inclination and 90% within safe anteversion. Only four hips (7.7%) were outliers, primarily in patients with severe preoperative dysplasia or obesity (BMI >30). No intraoperative complications related to cup placement occurred, and mean surgical time was 78 ± 12 minutes. At 3-month follow-up, the mean HHS improved significantly from 42.6 ± 8.4 preoperatively to 88.4 ± 6.2 (p<0.001), with no dislocations reported. Two patients had transient sciatic nerve palsy that resolved conservatively. Conclusion: Anatomical landmark-guided positioning of the acetabular cup in primary THA achieved high accuracy within the safe zone in the majority of cases, comparable to more resource-intensive navigation techniques. This simple, reproducible method offers a reliable alternative in settings with limited access to advanced technology, promoting consistent outcomes and low early complication rates. Further long-term studies are warranted to confirm durability.

Keywords: Acetabular cup positioning, anatomical landmarks, transverse acetabular ligament, total hip arthroplasty, Lewinnek safe zone, prospective study.