Design of an affordable, modular implant device for soft tissue tension assessment and range of motion tracking during total hip arthroplasty

Inexperienced surgeons undertaking hip arthroplasties are twice as likely to experience errors than their experienced colleagues, leading to dislocations, pain and discomfort for the patients. To address this issue, a new 3DOF force measurement system was developed and integrated in multiple new prototypes able to measure forces and movements intraoperatively in 3D. The prototypes were evaluated in three cadaver trials, with the goal of providing surgeons objective data to help determine the optimal implant fit and configuration. The devices comprise deformable polymer material that provide strain-based displacements measured with electromagnetic-based sensors and inertial measurement unit (IMU) for motion data. Device results show an accuracy of approx. 2 N and a sensitivity of approx. 1 N. Cadaver results indicated that soft tissue forces on the hip joint peak in the order of ~100 N and trend with positions of the leg during range of motion (ROM) tests, although force patterns differ between each cadaver. We propose that by monitoring forces and force patterns, in combination with standardised ROM tests, anomalies could be detected and corrected during surgery.