An Intraoperative Method for Measuring Acetabular Cup Inclination and Anteversion in Total Hip Arthroplasty Using an Inertial Measurement Unit

Abstract

Aiming to guide acetabular cup placement within the “safe zone” (40°±10° inclination, 15°±10° anteversion), this paper introduces an intraoperative inertial measurement unit (IMU)-based method for measuring cup orientation in total hip arthroplasty (THA), featuring registration and measurement phases. The registration phase establishes human-body-to-world coordinate transformations without reliance on bony landmarks or invasive contact, while the measurement phase enables real-time estimation of cup inclination and anteversion. Four experiments were conducted using a 3-axis tilt table to validate: 1) IMU’s basic angle estimation accuracy (RMSE 0.315°–0.423°); 2) robust acquisition of rotation axis vectors during the registration phase; 3) high measurement accuracy for inclination (RMSE 0.278°) and anteversion (RMSE 0.296°), with an average error vector magnitude of 0.373° (well within clinical tolerance); and 4) acceptable errors due to IMU pose changes (average error: 0.987°) and IMU drift (error increase: approximately 3.5-fold over 20 minutes, mitigated by mid-procedure reregistration). While theoretically and experimentally feasible, the method relies on patient-operating table immobility and lacks clinical validation. Offering high accuracy and cost-effectiveness, it shows potential as a standard THA navigation method with further optimization.