The skeletally fixed knee hinge for the grossly unstable knee.

This study examined whether a skeletally fixed prefabricated knee hinge can provide the intact or unstable knee with normal motion through a specific arc of motion. Eight cadaveric knee specimens were used. The amount of motion mismatch between knee and hinge motion was evaluated at six different knee flexion angles. With all knee ligaments intact, addition of the hinge resulted in increasing amounts of joint compression with knee flexion. When all knee ligaments were cut, there was some degree of distraction with 0 degrees of knee flexion, which seemed to gradually decrease and become compressive at 80 degrees of flexion. These values were not statistically significant. In contrast, the mismatch between anterior and posterior tibial translation mismatch was statistically significant. With the ligaments intact, the addition of the hinge resulted in increased amounts of posterior tibial translation, which became significant at 80 degrees of flexion. Similarly, when the ligaments were cut with the hinge intact, there was an increasing amount of posterior tibial translation, which became significant at 60 degrees of flexion. There was also a significant amount of anterior tibial translation at 0 degrees in this group. These results indicate that the hinge allows only a limited range of motion that does not significantly alter tibial translation or joint compression or distraction. Whether this amount of motion is enough to improve the outcome of the grossly unstable knee is unknown. The use of a more sophisticated hinge system might accomplish a greater range of anatomic motion before significant mismatch occurs between hinge and knee motion.