An Ex Vivo Patellofemoral Force-Sensing System for Next-Generation Prostheses Validation

Real-time measurement of patellofemoral (PF) contact forces could transform prosthesis design, surgical alignment, and rehabilitation protocols, yet no commercially available patellar component offers dedicated force sensing. We present a dual-channel acquisition system based on bisected Tekscan FlexiForce A401 sensors, a compact signal-conditioning board, and an Arduino Nano 33 BLE Sense for 10-bit digitization and real-time data streaming at 100 Hz. A fourth-order Butterworth filter (cutoff 5 Hz) cleans the raw voltages, which are then linearly mapped to force via bench-calibrated conversion factors, yielding a gain of $477\frac{{\text{N}}}{{\text{V}}}$ for the lateral channel and $347\frac{{\text{N}}}{{\text{V}}}$ for the medial channel. The instrumented patellar component was evaluated in an ex vivo cadaveric study (ethical approval obtained), in which a TKA-implanted lower limb was mounted in a customized fixture and subjected to three cycles of flexion–extension under quadriceps loads (20–280 N). The system clearly captured both lateral and medial contact forces with consistent peak–valley patterns and variability reflecting native trochlear geometry. Finally, we introduce a next-generation integrated PCB combining an ESP32-S3 wireless module for acquisition, processing, and streaming, dual-channel MCP6002 signal conditioning, and a Li-ion battery with on-board management—paving the way for future intraoperative use. This work establishes the quantitative and methodological groundwork for patient-specific, force-guided PF arthroplasty.