Smartphone-assisted technique in total hip arthroplasty can improve the precision of acetabular cup placement: a randomised controlled trial

Background: Malposition of the acetabular component mainly results from intraoperative pelvic motion and manual errors during cup placement. We investigated the outcomes of a device that uses a level indicator application of a smartphone to function as a pelvic tilt goniometer to assess intraoperative motion. The cup positions outside Lewinnek’s safe zone were compared between the smartphone-assisted technique and the conventional method that uses a mechanical alignment guide. Methods: A randomised controlled trial was conducted among 64 patients receiving primary cementless total hip arthroplasties (THAs) via a posterolateral approach from June 2015 to February 2017. Acetabular components were implanted either by conventional technique ( n = 32) or using smartphone technique ( n = 32). Inclination and anteversion angles were measured in supine pelvic radiographs. Results: The inclination angle in the smartphone group was not significantly different from the conventional group (41.2° ± 3.9° vs. 40.3° ± 7.9°, p = 0.567). The anteversion angle was also similar (19.3 ± 3.8° vs 19.1° ± 5.9°, p = 0.856). However, the standard deviation of the angle in the smartphone group was significantly lower for inclination ( p < 0.001) and anteversion ( p = 0.016). There were 3 outliers (9.4%) in the smartphone group, but 13 (40.6%) in the conventional group ( p = 0.008). The risk ratio was 0.23 (95% CI, 0.07–0.73). The risk difference was −0.31 (95% CI, –0.51– –0.11). Conclusion: The smartphone-assisted technique in THA improves the precision of cup placement and decreases the percentage of safe zone outliers. Thai Clinical Trials Registry (ID: TCTR20151123002).