A Sensorized 3-D Printed Gap-Gauge Aiming to Improve Knee Prosthesis Survival

Balancing unicompartmental knee arthroplasty is a knee replacement surgery routinely employed to relieve symptoms of arthritis. Knowledge of the forces applied by the ligaments to the prosthesis, as measured during the operation, is hypothesized to improve its longevity. This work builds upon the recently proposed 3-D printed depth gauge, an assistive tool as a means to quantify applied normal forces. We present an integrated sensor system consisting of a multimaterial (MM), 3-D printed, four-material sensor. The sensor is based on a differential capacitive measurement principle, measuring up to 15 N, and includes co-printed shielding which we show to be extremely effective in reducing parasitic capacitance fluctuations (35.7-53.9 dB). The integrated system includes an electronic interface based on a commercial capacitance-to-digital converter (CDC) and a ditto microcontroller. The sensor is printed into a 3-mm thickness gap-gauge that closely resembles the conventional spoon-shaped structure. The proposed design is characterized for both dynamic (0.1-0.7 Hz) and static excitations (2-14 N) and last, the shielding effectivity is demonstrated.