The mechanical placement of orthopedic magnets within the human knee joint

Abstract

A mechanical analysis of an orthopedic knee implant is presented. The analysis is performed on an orthopedic knee implant that utilizes repelling magnets placed on the articulating surfaces of the tibia and the femur. The repelling magnets theoretically serve to decrease the contact force and friction within the knee joint. A three-dimensional mathematical model of the human knee joint is utilized to analyze the mechanical effects of the implants within the knee. The geometry of the surface and the effects of the ligaments are incorporated into the model. The model is evaluated at several flexion angles. The placement of the magnets within the knee joint is varied, and magnet strengths are proposed. The model is then solved for the contact forces at the knee joint with and without the implanted magnets. The decrease in contact force due to the presence of the magnets within the knee joint is evaluated. The initial implant design consisted of a total of four magnets on the femoral surface, two medial and two lateral, and two magnets on the tibial surface, one medial and one lateral. The initial design was evaluated and the conclusion was made that a more effective design could be proposed. An implant that utilized a series of three magnets on both the medial and lateral femoral surfaces repelling against a single magnet placed on both the medial and lateral aspects of the tibial plateau was analyzed. The final conclusion was made that the alternate design using six magnets on the femoral articulating surface and two on the tibial articulating surface is indicated to be the preferred mechanical placement for magnets within the human knee joint. A summary of results for the initially proposed implant design and the alternative design options are presented.