A 6 degree-of-freedom testing rig for total knee replacements

Abstract

Osteoarthritis is the most common reason for loss of mobility in older patients, with knee replacement surgery being the only known cure for the disease. As the number of patients with osteoarthritis has increased over recent years, and with patient dissatisfaction after knee replacement surgery still common, testing of total knee replacements (=TKR) is required to improve implant performance. Evaluation of the performance of TKRs requires special testing rigs to be performed without resorting to patient implantation and subsequent testing. In this work a novel, 6 degree-of-freedom testing rig for TKRs is proposed. The rig is based on electromechanical actuators. It directly integrates the Grood and Suntay Joint Coordinate System for describing three-dimensional joint motion into the testing rig, featuring three rotational and three translational axes. The rig is designed to maximize stiffness to reduce measurement errors due to rig compliance. It allows for force and displacement control in all 6 controlled axes, using electromechanical actuators for all movements. Rotational movements are controlled using belt drives. The rig is designed for up to 6 kN axial load on the knee, allowing for simulation of running, jumping, or stair climbing.