Error and risk factors in augmented reality-guided cup placement during total hip arthroplasty

Augmented reality (AR)-based navigation has gained popularity in total hip arthroplasty (THA) due to its imageless, user-friendly approach. However, factors influencing the accuracy of cup placement remain unclear. This study aimed to evaluate the accuracy of AR-guided cup placement and identify risk factors associated with placement error of 5°or more.

This retrospective, single-center study included 128 patients (132 hips) who underwent THA with AR-based navigation in the lateral decubitus position. Postoperative cup positioning was assessed via X-rays and computed tomography scans. Absolute errors in intraoperative and postoperative measurements, along with the achievement of the combined anteversion (CA) safe zone, were calculated. Patients were divided into two groups based on cup placement errors of ≥5°. The associations of patient demographics and spinopelvic parameters with cup anteversion and inclination malalignment were analyzed using logistic regression models with Firth's penalized likelihood.

Mean absolute errors were 2.8° ± 2.2° for cup anteversion and 3.1° ± 2.8° for cup inclination, with 92 % of cases achieving the CA safe zone. Errors of ≥5° were found in 28 hips (21 %) for anteversion and 24 hips (18 %) for inclination. After adjusting for confounders, Firth's penalized multivariable logistic regression analysis identified significant associations between malaligned anteversion and body mass index (BMI) (odds ratio [OR], 1.16; 95 % confidence interval [CI], 1.03-1.32; P = 0.01) and pelvic obliquity (PO) (OR, 1.47; 95 % CI, 1.11-1.98; P = 0.01). Malaligned inclination was also significantly associated with PO (OR, 1.96; 95 % CI, 1.47-2.78; P < 0.001).

AR-based navigation achieved cup placement accuracy comparable to previous reports. However, PO was associated with greater differences between intraoperative navigation and postoperative radiographic measurements for both anteversion and inclination, while higher BMI was associated with anteversion differences. Careful pelvic landmark registration is advised in such patients.