Influence of total knee arthroplasty on patellar kinematics and contact characteristics

Femoro-patellar complications are one of the most common problems after total knee arthroplasty (TKA). TKA components that reduce patellar loads and preserve physiological patellar kinematics should reduce these problems. Therefore, we evaluated the patellar kinematics and the retro-patellar contact characteristics in both the intact knee and in the TKA-knee. Eight Thiel-embalmed cadaver knees were tested first intact and then after TKA using rotating as well as gliding inlay and with additional patellar resurfacing while flexing the knee from 0A degrees to 100A degrees. During the examination quadriceps and hamstring forces were applied. TKA with additional patellar resurfacing led to an increased retro-patellar pressure, a decreased contact area and an increased lateral movement. Although patellar kinematics could not be changed by using a gliding inlay compared to a rotating inlay, the gliding inlay improved retro-patellar contact characteristics by reducing the pressure and increasing the contact area, especially in higher flexion. The increased retro-patellar pressure together with the increased lateral movement of the patella after TKA may be one important cause for anterior knee pain appearing after TKA. In view of the improved retro-patellar contact characteristics using a gliding inlay this inlay should be preferred, providing that the posterior cruciate ligament is intact.