Novel rabbit model of moderate knee contracture induced by direct capsular damage.

The treatment of joint contracture continues to represent a challenging problem in orthopedic surgery and rehabilitation medicine. Existing animal models of knee contracture for evaluating new treatments are mostly created by extensive joint tissue damage with Kirschner-wire immobilization which requires a second surgery to remove Kirschner-wires. This study aimed to develop a less invasive rabbit model of moderate knee contracture through a single surgery. Skeletally mature New Zealand White rabbits had their right knee operated to create surgical damage to the posterior capsule under direct visualization. Operated knees were then held in a flexed position by suturing the superficial flexion muscles with absorbable sutures. The flexion contracture (net extension loss) was determined by comparing the extension angles between the operated and non-operated knees from 8 to 24 weeks post-surgery. The flexion contracture of the operated knees was significantly greater (p < 0.01/0.001) than the non-operated knees at each weekly measurement. The mean flexion contractures were 22° at 8 weeks, 19° at 16 weeks, and 18° at 24 weeks. No significant differences in the severity of flexion contracture were observed between 8-week and each of the following weeks, suggesting that the flexion contracture was essentially stabilized by 8 weeks post-surgery. Histopathologic analyses demonstrated intra-articular and peri-articular scar formation. This less invasive rabbit model of moderate knee contracture is more quickly established through a single surgery with lower risk of surgical complications compared to the previously reported invasive models, and could be an alternative animal model for joint contracture research. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2687-2695, 2018.