Extract
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.