Biomechanical study of myogenic factors in the contracture period of traumatic elbow joint

Elbow contracture is a common complication following elbow trauma. Soft tissue fibrosis is an important cause of exogenous joint contracture. The most effective non-surgical method for preventing and treating elbow contracture is stretching exercise. However, there is currently a lack of understanding of the local mechanical environment of the joint, and difficulties exist in the timing and mode of loading during treatment.

This study established an animal model of elbow contracture and built a mechanical experimental platform to explore its morphological evolution patterns. The range of motion, stiffness changes of the contracted joint caused by myogenic contracture, and the mechanical and morphological changes of the biceps brachii were evaluated at 2, 4, 6, and 8 weeks, respectively.

We found that the joint extension stiffness decreased by 24.4 %, 19.8 %, 7.3 %, and 5.3 % compared with the control group at 2, 4, 6, and 8 weeks, respectively. Within 2-6 weeks of elbow contracture, the dynamic stiffness, static stiffness, and viscosity of the muscle all increased with time, and the cross-sectional area of the biceps brachii continued to decrease until it stabilized at 6 weeks, with a reduction of 30 % compared to the control group. Within 2-8 weeks of elbow contracture, the proportion of collagen deposition in the biceps brachii continued to increase. Compared with 2 weeks, the percentage of collagen deposition in the biceps brachii increased by 164.7 % at 8 weeks.

During traumatic joint contractures, as the contractures developed over time, myogenic contractures could continue to limit joint range of motion and affect joint stiffness.The changes in muscle mechanical properties during joint contracture could be attributed to changes in muscle cross-sectional area and collagen deposition.