Validation of an Augmented Reality Based Functional Method to Determine and Render the Hip Rotation Centre During Total Hip Arthroplasty.

BACKGROUND: We present a method to determine and visualise the functional centre of rotation (FCOR) of the hip during total hip arthroplasty using an augmented reality head mounted display (AR-HMD). METHODS: We developed software allowing a HoloLens to provide inside-out infrared tracking of markers affixed to cadaver femurs and 3D printed acetabuli. Two observers rotated 20 cadaver femurs twice in a matching cup, producing 80 measurements. The FCOR of the acetabulum and femoral head was determined based on the point cloud generated from the displacement of the femoral trackers to the acetabular tracker. RESULTS: Compared to the ground truth, the FCOR resulted in an absolute error of 2.9 ± 1.4 mm for the acetabulum and 2.9 ± 1.2 mm for the femur, with 95th percentiles below 5.6 and 4.7 mm. CONCLUSION: The proposed AR-HMD system offers an accurate and reproducible way to determine the femoral and acetabular FCOR in an experimental setting.