The Coventry Award Paper - Mobility and contact mechanics of a rotating platform total knee replacement

Despite their increasing clinical use, mobile-bearing total knee replacemen ts have not been well characterized biomechanically. An experimental and fi nite element analysis was done to assess the mobility and contact mechanics of a widely used rotating platform total knee replacement. Parameters that varied were axial load, condylar load allocation, flexion angle, and stati c versus dynamic loading. Similar results from the physical model and finit e element model lend credence to the validity of the findings. The torque r equired to initiate rotation (static torque) was greater than that to susta in rotation (dynamic torque). At four times body weight axial load, peak re sisting torque measured was 9.47 +/- 0.61 and 5.51 +/- 0.38 N-m, for static and dynamic torque, respectively. A 60-40 condylar load allocation produce d slightly less resisting torque than the 50-50 load. For all practical pur poses, the polyethylene insert rotated simultaneously with the femoral comp onent, leading to maintenance of high contact area, desirable behavior clin ically. Walking cycle simulations produced a total axial rotation range of motion of 6 degrees. The high frictional torques observed at the mobile int erface may explain why a percentage of these mobile-bearings fail to rotate under routine functional load.