Dislocation of rotating hinge knee prostheses. A report of four cases.

The rotating hinge knee mechanism was designed to provide a stable total knee reconstruction when the intrinsic stability of the knee has been lost as a result of severe soft-tissue compromise1-5. It is not recommended for routine total knee arthroplasty because it has been associated with high rates of revision2,3. Rotating hinge knee designs have a transversely (horizontally) oriented hinge axis for flexion-extension motion and a vertically oriented post-in-channel axis for internal and external rotation (Fig. 1). The post-in-channel design also allows distraction up to the limits imposed by soft-tissue tension. As a result, component dislocation due to distraction disengagement is prevented only by the restraint of the soft-tissue envelope. Once distraction occurs, the degree of tilting of the central rotational stem within the channel directly reflects the intrinsic stability of the component design. The amount of distraction required for implant dislocation is directly related to the length, degree of taper, and tolerance of the stem in the cylinder (Fig. 1). To our knowledge, only one design (Link America, Pine Brook, New Jersey) possesses an antisubluxation feature that specifically prevents implant distraction. There have been few reports in the literature with regard to the clinical stability afforded by these rotating hinge knee prostheses1,2,5, and we are aware of no reports comparing the clinical stability provided by the various rotating hinge knee mechanisms. We therefore conducted a retrospective review to assess the prevalence of instability and dislocation in a consecutive series of rotating hinge total knee prostheses of various designs, and we identified four dislocations. Fig. 1 Line diagrams illustrating the minimal varus-valgus toggle and hence the excellent stability provided by designs that employ a long (7-cm) vertical, cylindrical rotational stem within a cylindrical channel compared with the excessive …