Biomechanical study of protonation movement during the healing phase after elbow joint capsule and ligament trauma in rabbits.

Purpose: This study aimed to construct a forelimb contracture model in rabbits to mechanically quantify pronation-supination movements during the healing phase following joint capsule and ligament injuries. Additionally, a finite element model of the human elbow joint was developed to investigate the mechanical environment of the elbow joint during pronation-supination movements in the healing phase. Methods: White rabbits were randomly assigned to either a control group (no injury) or an injury group (joint capsule and ligament injury). The injured forelimbs were immobilized for 2, 4, 6, and 8 weeks (designated as 2IM, 4IM, 6IM, 8IM groups, respectively), and mechanical tests were performed on the joints. A finite element model of the human elbow joint was utilized to simulate elbow joint protonation from 0° to 50° during different healing periods, and changes in soft tissue forces within the elbow joint were analyzed. Results: During the healing phase, the injured group experienced significant reductions in total range of motion (ROM), with decreases of 26.8°, 43.8°, and 57.4° at 4 IM, 6 IM, and 8 IM, respectively. These reductions were accompanied by histological phenomena such as cellular adhesion within the joint capsule. Additionally, internal soft tissue stress gradually increased over time, with the highest stress observed in the annular ligament. Throughout the healing process, stress on the humeral cartilage consistently exceeded that on the ulnar cartilage, with the maximum stress reaching 15.8 times that of the ulnar cartilage. Stress on the joint capsule also increased progressively, rising by 69.5 %, 87.5 %, and 139.2 % at 4, 6, and 8 weeks post-injury, respectively. Conclusion: Healing time is significantly negatively correlated with total joint range of motion, as evidenced by the continuous accumulation and transfer of internal soft tissue loading. These findings are associated with worsening histological changes within the joint capsule. These results are of great significance for further understanding the biomechanical environment within the joint cavity during elbow contracture and for guiding elbow contracture release surgery.