Pilot validation study on a quasi-static weight-bearing knee rig

This article presents a pilot study on a quasi-static knee rig designed to investigate the influence of pathologies and surgical interventions on the patellofemoral kinetics of cadaveric knees. The knee rig allows cadaveric knees to flex and extend under a simulated body weight by transmitting a force to the quadriceps tendon. During the squat simulation, the ground reaction force stays within physiological values. Before using this device to answer clinical questions, two knee specimens were tested to assess the repeatability of the rig. Four repeated flexion–extension cycles were performed under a simulated body weight of 700 N, with an isolated force on the quadriceps tendon up to 2700 N and with a ground reaction force close to 350 N. The resulting patellofemoral contact area shifted from distal to proximal during knee flexion. From 20° to 60° of knee flexion, the mean contact area and pressure increased from 80.2 ± 3.3 to 349.5 ± 10.1 mm² and from 0.9 ± 0.2 to 5.9 ± 0.7 MPa, respectively. The transmitted force on the quadriceps tendon, the ground reaction force and the patellofemoral contact area and pressure were continuously measured and showed a relative variability of 1.6%, 2.4%, 2.8% and 3.2%, respectively. The presented knee rig shows a good repeatability that allows us to use this knee rig to quantify the influence of anatomical changes on the patellofemoral contact area and pressures during a squat simulation.