Accuracy of leg length changes in total hip arthroplasty using a computed tomography-based augmented reality navigation system

Leg length is an important consideration in total hip arthroplasty (THA) as leg length discrepancies (LLD) after THA cause poor outcomes and medical litigation. This study aimed to investigate the accuracy of computed tomography (CT)-based navigation with augmented reality (AR) technology for measuring intra-operative leg length change using anteroposterior radiography (two-dimensional, 2D) and CT (three-dimensional, 3D).

This study included 71 patients (75 hips) who underwent primary cementless THA in the supine position between June 2022 and November 2023 using the HoloNavi One. To assess the accuracy of the HoloNavi One based on 2D and 3D measurements, the absolute error between the intra-operative leg length change and the 2D and 3D measurements was evaluated, and the correlations were investigated. Additionally, factors affecting the absolute error were examined using multivariate analysis.

The mean intra-operative leg length change when using the HoloNavi One was 6.5 ± 5.0 mm, while the mean leg length change on the 2D and 3D measurements were 5.9 ± 4.8 mm and 4.6 ± 5.7 mm, respectively. The mean absolute errors were 2.3 ± 2.7 mm between the HoloNavi One and 2D measurements, and 3.8 ± 3.3 mm between HoloNavi One and 3D measurements. The absolute errors in leg length changes for the 3D measurements were greater than those for the 2D measurements (p < 0.01). Positive correlations of leg length changes were found between the HoloNavi One and the 2D and 3D measurements. In the multiple regression analysis, no significant factors affecting the absolute error were identified in either the 2D or 3D measurements.

CT-based navigation with AR technology in the supine position provided acceptable accuracy for leg length change measurements.