Description and validation of a portable system for biomechanical ex vivo knee kinematics and laxity assessment in simulated intra-operative scenarios.

Purpose: The analysis of knee joint biomechanics under intraoperative-like conditions is fundamental to support surgical decisions and improve clinical outcomes. Many experimental systems developed in recent years are characterized by high complexity and limited portability, which may restrict the reproduction of surgical intraoperative workflows. Therefore, this study describes the design and experimentally validates a compact and portable testing platform capable of accurately analysing knee tibio-femoral and patello-femoral kinematics and laxity under intraoperative-like conditions. Methods: The system integrates motion capture, mechanical fixation, motor-driven actuation, force measurement and dedicated software into a unique platform. It enables passive and active open-chain knee motions, as well as standardized ligament laxity testing. Tibio-femoral and patello-femoral kinematics are simultaneously recorded while quadriceps and external forces are measured respectively through mono-axial and tri-axial load cells. System accuracy and repeatability were assessed through load cell calibration and dynamic testing on a synthetic knee model. Transportability, setup time and overall performance were evaluated under realistic ex vivo experimental conditions. Results: Validation demonstrated close agreement between set and measured loads, with measurement accuracies of approximately 1% for quadriceps forces and 0.75% for externally applied knee forces. Motor-driven motion showed high repeatability, with mean standard deviations of 0.51° for flexion-extension cycles and 1.62° for multiple dynamic flexion tests. Motion capture calibration achieved a pointer tip positional error of approximately 0.20 mm. Ex vivo testing confirmed reliable reproduction of knee motion and highly reproducible measurement, with rapid set-up and workflow smoothness. Conclusion: The system represents a portable, accurate, repeatable and validated experimental platform for biomechanical assessment of knee joint kinematics and laxity under intraoperative-like conditions. Its modular design, rapid setup and capability to combine kinematic and kinetic measurements make it a valuable tool for investigating the biomechanical impact of surgical techniques or implants, and patient-specific joint behaviour in ex vivo settings. Level of Evidence: N/A.