Smartwatch-based pelvic tracking system for augmented reality navigation in total hip arthroplasty: a preliminary clinical study

BACKGROUND: Accurate assessment of pelvic orientation is essential for acetabular cup placement during total hip arthroplasty (THA). Conventional pelvic tracking systems generally rely on dedicated tracking hardware and optical tracking infrastructure. We developed a smartwatch-based pelvic tracking system integrated with an augmented reality (AR) navigation platform and evaluated its preliminary clinical performance. METHODS: This retrospective study included 30 hips of 27 consecutive patients who underwent primary THA using a smartwatch-based pelvic tracking navigation system between May 2025 and April 2026. The system utilizes a commercially available smartwatch fixed to the iliac crest as a pelvic tracking device and communicates orientation information to a smartphone-based AR navigation platform via Bluetooth. Acetabular cup orientation was evaluated using postoperative CT. Absolute radiographic inclination (RI) and anteversion (RA) errors were calculated as absolute differences between the final intraoperative navigation measurements and postoperative CT measurements. RESULTS: The mean absolute RI error was 2.8° ± 2.1°, and the mean absolute RA error was 3.6° ± 2.2°. Postoperative CT measurements were within 5° of the final intraoperative navigation measurements for RI and RA in 86.7% and 70.0% of hips, respectively. Navigation was successfully completed in all 30 hips, with no conversion to a backup technique. Additional bench testing demonstrated reproducible smartwatch reattachment and reduction of time-dependent relative orientation differences following FPP invocation. CONCLUSIONS: This study demonstrated the feasibility of integrating a commercially available smartwatch into a pelvic tracking system for THA navigation. The smartwatch-based pelvic tracking platform achieved a preliminary range of cup-positioning accuracy without requiring continuous optical visualization of a pelvic reference marker while utilizing a compact and widely available consumer wearable device. This study represents the first step toward wearable-device-based navigation in arthroplasty.