Investigation of the intrameniscal forces : experiment on porcine knee joints and formulation of mathematical models

Abstract

Mechanisms of the knee joint have always been of interest to orthopaedic surgeons, prosthesis designers and biomechanical engineers. Meniscal injuries are common and the impact of such injuries on the patients is tremendous. Therefore, it is of great interest to investigate the load transmission mechanism in the knee and especially in the menisci. In this project, the load transfer mechanism was investigated through the direct measurement of the intrameniscal forces of the porcine knee joint using miniature sensors. Such attempts will provide quantitative indications into the load distribution and provide insights into the failure mechanism of the natural knee. In this report, variation of intrameniscal stress with joint angulations, applied torque and time were determined. This approach is unique as there has been no attempt in measurement of the forces inside the meniscus. In addition, mathematical models of the articular cartilage and meniscus are derived to explain the variation of intrameniscal stress with time. From the investigations done on the intrameniscal force, it was found that measurement of intrameniscal force is possible. In a porcine knee joint, anterior region of the lateral meniscus experienced high stresses during hyperextension. During hyperflexion, posterior regions of both lateral and medial menisci were under high stresses. Anterior region of the lateral meniscus was under highest stresses during external rotation and posterior region of the lateral meniscus was under highest stresses during internal rotation of the knee joint. In general, higher stresses were observed during external rotation as compared to internal rotation of the porcine knee. Highest stresses typically occur in extreme joint positions (hyperextension, hyperflexion, internal rotation and external rotation) and these suggest that extreme positions with high applied torque and a combination of extreme positions on the knee joint should be avoided. Experimental results for variation of intrameniscal stress with time implied that there was a load transfer from articular cartilage to meniscus with time. This load shift behaviour will protect the articular cartilage if the knee joint is under static loading. This stress versus time behaviour can be explained by a viscoelastic power-law model.