We describe 5 cases of failure of the locking mechanism of the polyethylene insert and tibial base-plate in one design of constrained condylar knee prosthesis due to disengagement of the locking screw. Loosening of the screw is believed to occur because of a counterclockwise torque created by the axial rotation of the femur on the tibia that occurs as the knee extends during gait. This torque is transmitted via the highly rotationally constrained femoral housing and tibial post to the locking screw. These failures suggest that an alternative locking mechanism should be considered for this prosthesis.
Copyright © 2011 Elsevier Inc. All rights reserved.