Assessment of healing of grade III posterolateral corner injuries: an in vivo model.

The primary purpose of this study was to test the hypothesis that an in vivo model of posterolateral knee instability could be created in the rabbit and to develop a natural history model in animals. The biomechanical and gross features of the rabbit knee 12 weeks after rupture of the fibular collateral ligament (FCL) and popliteus tendon were investigated in 14 skeletally mature New Zealand white rabbits. In the operated leg both the FCL and popliteus tendon were traumatically ruptured near their respective femoral insertions and the contralateral leg served as the control. At 12 weeks, the legs were removed for analysis of healing by both gross analysis and by biomechanical testing of knee joint stability. Biomechanical testing of varus-valgus knee rotation as well as concurrent coupled external rotation was performed to measure the amount of force necessary to produce a uniform amount of displacement. Grossly, only one of the FCLs and none of the popliteus tendons healed. Biomechanical testing revealed a statistically significant difference in the amount of force necessary to achieve 10 mm displacement for the operative versus the contralateral control knee for varus at 30 degrees (p<0.001), 60 degrees (p<0.006), and 90 degrees (p<0.01). Our data supports the clinical observations of human grade III posterolateral corner (PLC) injuries, which appear to undergo minimal healing and generally result in poor outcomes with conservative treatment, that the FCL or popliteus tendon rarely heal when torn. This initial study of healing and knee stability after PLC injuries in rabbits supports the further study of in vivo animal models for evaluation of posterolateral knee injuries.