An in vivo injury model of posterolateral knee instability

Background: Posterolateral knee instability is a difficult clinical problem to diagnose and treat. To best evaluate its natural history and the effects of interventional treatments, it is important to develop an in vivo model in an attempt to validate human cadaveric and clinical observational studies. Purpose: To develop an in vivo model of posterolateral knee instability in the rabbit and to determine the natural history of untreated posterolateral knee injuries at 6 months postoperatively. Study Design: Controlled laboratory study. Methods: The fibular collateral ligament and popliteus tendon were surgically transected in 1 knee in each of 10 skeletally mature New Zealand White rabbits, with the contralateral knee serving as a control knee. At 6 months postoperatively, the rabbits were euthanized, the knees were removed, and biomechanical testing of knee joint stability was performed. After biomechanical testing, histological sections of each proximal tibia and distal femur were evaluated, and each proximal tibia was graded using an osteoarthritis grading scheme. Results: Biomechanical testing revealed a statistically significant difference in amount of rotation in the operated knees compared with the unoperated control knees to varus moments at 30°, 60°, and 90° and to external rotation torques at 30° and 60°. Morphological analysis revealed no significant difference in lesions of osteoarthritis in the medial compartment of the operated knees compared with the unoperated knees. Conclusions: Although the presence of posterolateral knee instability was validated 6 months after surgery in this model, the authors did not identify significant differences in lesions of osteoarthritis in the operated knees compared with the unoperated control knees. Clinical Significance: This study confirms that posterolateral knee instability can be created in an animal model. It also recapitulates the clinical observation in humans that untreated posterolateral knee injuries do not heal. Similar to animal models of medial collateral ligament sectioning, further studies to validate a posterolateral instability knee model may lead to interventional studies to determine the best way to treat this complex knee instability pattern.