Abstract: BACKGROUND: Previous studies have shown that the modified Tsuge suture method can be used to repair chicken tendon injuries. However, the lack of post-repair functional exercise leads to obvious tendon adhesions. Therefore, a functional exercise after tendon repair is very important.
OBJECTIVE: To explore a scheme for passive functional exercise against tendon adhesion in a chicken model of flexor toe tendon rupture following repair using the modified Tsuge suture method.
METHODS: A total of 100 Sanhuang chickens, 10 months of age, were taken to make animal models of deep flexor tendon II rupture of the third toe of the right foot. Animal models were randomized into five groups (n=20 per group): groups A, B, C and D were given plaster immobilization for 3 weeks after surgery, and were simultaneously given passive functional exercise 1, 2, 3, and 0 times a day for 3 weeks, respectively; group E had  neither plaster immobilization nor passive functional exercise after surgery. The gross morphology of the chicken claw, the morphology of the tendon anastomosis end and the degree of peritendinous adhesion were observed. The slipping distance of the deep flexor tendon of the third toe, the flexion angles of all joints, the pathological morphology of the tendon at the anastomotic end and the hydroxyproline content were measured. 
RESULTS AND CONCLUSION: The tendon of group E was completely ruptured around 6 day after surgery and was removed from the experiment. The chicken claws in groups B and C had better grasping morphology, group D had almost no grasping morphology, and group A had worse grasping morphology than groups B and C. In groups B and C, the tendon anastomosis end was not obviously expanded, with the texture similar to that of normal tendon tissue. Compared with group C, tendon adhesion was relatively mild in group B. In group D, the tendon anastomosis end was obviously expanded, with the hard texture, obvious peritendinous scar and serious adhesion. Expansion at the tendon anastomosis end was more obvious than groups B and C but less severe than group D. The slipping distance and the related flexion angles of the deep flexor tendon of the third toe were better in groups B and C than groups A and D (P < 0.05). The content of hydroxyproline in the tendon of chickens in group B was higher than those in groups A, C and D (P < 0.05). Findings from hematoxylin-eosin and Sirius red staining showed that collagen fibers of the tendon in groups A, C and B were gradually arranged in a directional manner, where the number of bright red and thick type I collagen fibers was gradually increased and the number of tiny green type III collagen fibers was gradually decreased. In group E, collagen fibers of the tendon were poorly arranged in a directional manner and type I and type III collagen fibers were cross-distributed. To conclude, adequate passive functional exercises twice a day following repair with the modified Tsuge suture method could effectively alleviate tendon adhesion and reduce tendon rupture in the chicken model of deep flexor tendon rupture.

Key words: tendon injury, animal experiment, tendon adhesion, passive functional exercise, deep flexor tendon, plaster immobilization