Evaluating the Impact of Initial Injury Severity on Post-Traumatic Joint Contracture in a Rat Elbow Model

Post-traumatic joint contracture (PTJC) is a common complication following elbow injuries, often leading to stiffness, pain, and impaired limb function. A simple elbow dislocation model in Long-Evans rats has been validated to replicate clinical PTJC. However, real-world elbow trauma frequently involves more complex injuries such as chronic instability or fracture dislocation. The objective of this study was to evaluate outcomes of two newly developed, more severe elbow injuries in vivo for the first time. A three-tiered injury model of increasing severity was implemented: Tier I (simple dislocation), Tier II (instability), and Tier III (fracture dislocation). Mechanical hyperalgesia thresholds, forelimb strength, gait, and elbow range of motion were assessed. Results showed that all injury groups exhibited significantly reduced mechanical hyperalgesia thresholds and forelimb strength ratios compared to controls, but no significant differences were observed between the three injury groups. These findings suggest that despite increased initial injury severity, PTJC outcomes were largely similar among dislocation, instability, and fracture injury models. Limitations include small sample sizes and ongoing data collection for gait, ROM, and post-mortem analysis. This study is an important step in understanding how different injury mechanisms contribute to PTJC progression and may inform future clinical strategies for prevention and treatment.