Persistent motion loss after free joint mobilization in a rat model of post-traumatic elbow contracture

Background Post-traumatic joint contracture (PTJC) in the elbow is a challenging clinical problem due to the anatomical and biomechanical complexity of the elbow joint. Methods We previously established an animal model to study elbow PTJC, wherein surgically induced soft tissue damage, followed by 6 weeks of unilateral immobilization in Long-Evans rats, led to stiffened and contracted joints that exhibited features similar to the human condition. In this study, after 6 weeks of immobilization, we remobilized the animal (ie, external bandage removed and free cage activity) for an additional 6 weeks, after which the limbs were evaluated mechanically and histologically. The objective of this study was to evaluate whether this decreased joint motion would persist after 6 weeks of free mobilization (FM). Results After FM, flexion-extension demonstrated decreased total range of motion (ROM) and neutral zone length, and increased ROM midpoint for injured limbs compared with control and contralateral limbs. Specifically, after FM total ROM demonstrated a significant decrease of approximately 22% and 26% compared with control and contralateral limbs for injury I (anterior capsulotomy) and injury II (anterior capsulotomy with lateral collateral ligament transection), respectively. Histologic evaluation showed increased adhesion, fibrosis, and thickness of the capsule tissue in the injured limbs after FM compared with control and contralateral limbs, which is consistent with patterns previously reported in human tissue. Conclusion Even with FM, injured limbs in this model demonstrate persistent joint motion loss and histologic results similar to the human condition. Future work will use this animal model to investigate the mechanisms responsible for PTJC and responses to therapeutic intervention.