Bio-Mimetic Design and Performance Analysis of Passive Polycentric Knee Joint

Polycentric knee prosthesis use four bar mechanism to enable natural gait performance by amputees. Human knee primarily comprising of 3 bones, namely femur, tibia and patella along with ligaments called ACL (anterior cruciate ligament), the PCL (posterior cruciate ligament) which restrain the motion between bones. Conventional Single axis knee prosthesis rely on friction adjusted by a bolt for gait control. Other expensive knee prosthesis use hydraulic system to regulate swing of prosthetic shin with change in walking speed. Both hydraulic and friction knees can be either single axis (or polycentric) in nature. A polycentric human knee joint enables the femur to roll and slide on tibial plateau. This paper talks about a passive prosthetic knee joint design which has coupler link acting as ligaments and knee stiffness similar to that of natural knee. Resistive torque by tendons in natural knee was replicated using non-linear spring element in prosthetic model. Spring element tested under tensile load showed 3 phase stiffness characteristics similar to that of knee tendons. Kinematic analysis of linkages and stress analysis of knee joint was carried out. 3D printed prototype was tested to validate kinematic performance of prosthetic knee joint in comparison with the natural knee torque characteristics.