Dislocation of an artificial knee component due to extraordinary function.

A rare complication, namely dislocation of a knee component without fracture of the prosthesis and not caused by a trauma, is described in a patient who was treated for osteosarcoma of the femur. Probably the dislocation, which occurred 2 years postoperatively, was caused by an extraordinary function of this prosthesis. A partial revision of the prosthesis was performed. The newly designed knee component, which prevents dislocation, is described.