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 ( = 32) or using smartphone technique ( = 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°,  = 0.567). The anteversion angle was also similar (19.3 ± 3.8° vs 19.1° ± 5.9°, = 0.856). However, the standard deviation of the angle in the smartphone group was significantly lower for inclination (< 0.001) and anteversion (= 0.016). There were 3 outliers (9.4%) in the smartphone group, but 13 (40.6%) in the conventional group ( = 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).