The Study of Contact Pressure of a Customized Knee Spacer Using Finite Element Analysis

摘要

With one-third of patients having osteoarthritis predominantly in one compartment of the knee, unicompartmental knee spacers have been introduced as a less invasive alternative to total knee replacement. However, patients with the knee spacer implanted were seen to have persistent pain, resulting in high revision rates. A static computational finite element model of the knee at full extension and 90° flexion, mimicking the peak tibio-femoral force at heel strike during gait and peak joint forces during an ascending motion from a squatting position was used to study the tibio-femoral contact pressure of different designs and proper-ties of the knee spacer. Three designs (contoured - conventional, flat and C-shaped) of the knee spacers were created and simulated with three different materials (cobalt-chromium, UHMWPE and polyurethane). The average contact pressures acting at the medial compartment of the femoral condyle were extracted for analysis. Spacers made out of soft material exerted lesser contact pressure onto the femur cartilage. In the full extension model, using a soft material of polyurethane, the C-shaped spacer exhibited the lowest femoral cartilage contact pressure with a 31% and 18% decrease from the flat and contoured spacers respectively. In the 90° knee flexion model, the contoured spacer had the lowest contact pressure among the other spacers. Contoured spacers made of polyurethane exhibited a 13% and 20% decrease from the flat and C-shaped spacers respectively. Therefore, it is suggested that the knee spacers should be made out of a softer material that can withstand the joint forces in various motions and have a geometry that would increase the contact area of the between the joints.