Comparison between a Constrained Condylar and a Rotating Hinge in revision knee surgery.

The performance of Constrained Condylar and Rotating Hinge types of total knee replacement was compared by mechanical testing, by using the Knee Society Clinical and Radiographic evaluations, and by a self-assessment questionnaire. In mechanical tests to evaluate varus strength, Constrained Condylars developed at least 6 degrees of varus rotation, but there was minimal varus rotation in the Rotating Hinges. This was reflected in the stability scores in the Knee Society evaluation. The shorter stems used in the Constrained Condylars resulted in a higher variation in femoral-tibial angles, and a smaller than ideal valgus angle. Radiographically, the only radiolucent lines observed were those adjacent to the joint itself, and there was no difference between the two types of total knee replacement. From the questionnaire, there was a high correlation in the performances between the operated and non-operated knees in the Rotating Hinge group. This indicated the Hinges were capable of matching their performance to a required level, thereby producing a better overall clinical result. In summary, the study indicated that a Rotating Hinge type should be given greater consideration, particularly if the disadvantages of larger bone resection and longer stems could be overcome.