Establishment Of Animal Model Of Patella-patellar Tendon Junction Injury From Jumping And Effect Of Post-exercise Cryotherapy On Injury

Objective:The purpose of this study was to establish patella-patellar tendon junction(PPTJ) injury model from jumping and eccentric exercise model, which were used to investigate the effects of acute and chronic jumping on histological changes and expression of related cytokines in patella-patellar tendon junction, and to explore the effect of post-exercise cryotherapy.Method:part Ⅰ:15 18-week old New Zealand rabbits were divided into 2-week group (W2) and 4-week group (W4) and control group (Con). The animals was trained to jump by self-devised rabbit jumping instrument for 150 times a day,5 consecutive days a week. The PPTJ was harvested and sections were stained by HE and safranin 0 to evaluate histological changes, and immunohistochemistry was used to display the expression of factors related with angiogenesis, inflammation, tissue repair and et al. Part Ⅱ:The rabbits were divided into exercise group and cryotherapy group and control group, exercise scheme was the same with part Ⅰ, This study was to explore the interventional effect of post-exercise cryotherapy on PPTJ injury, and to observe the effect of post-exercise cryotherapy on muscle physical state. Part Ⅲ:The rabbits were divided into acute exercise group and post-exercise cryotherapy group and control group. The rabbits were trained to accomplish drop-landing exercise for 200 times by the novel eccentric exercise instrument. Histological changes and levels of growth factors and inflammatory factors was evaluated at 2h and 24h and 48h after exercise, and effect of post-exercise cryotherapy on muscle physical state was also observed.Result:part Ⅰ:Compared with Con group, W4 group displayed disorganized collagen fibers and uneven distribution of cells and glycosaminglycans, cell density was increased significantly(p<0.05),fibrocartilage zone thickness was increased (p<0.01). The density of cells expressing Collagen Ⅲ was significantly increased(p<0.01), the ratio of ColⅢ/Col Ⅰ was increased significantly, The density of cells expressing IL-6, COX-2, HIF-1Alpha, VEGF, TGF-beta 2, BMP, Caspase-3 was increased significantly (P<0.01), The density of cells expressing SP was increased (P<0.05). Part Ⅱ:There was no significant difference in histomorphology and collagen expression between exercise group and cryotherapy group, The density of cells expressing IL-6 and Cox-2 in cryotherapy group was lower than that of exercise group. cryotherapy can reduce muscle hardness and muscle tension in the first week. Part Ⅲ:In the acute exercise group,there was no obvious changes in histomorphology compared with control group, the density of cells expressing IL-6 and COX-2 reached maximum value at 2h after exercise, the density of cells expressing Collagen Ⅰ, Collagen Ⅲ, and TGF-beta 2 reached maximum value at 24h after exercise, the density of cells expressing bFGF reached maximum value at 48h after exercise, significantly higher than that of Con group (P<0.01). The density of cells expressing IL-6 and COX-2 of post-exercise cryotherapy group was significantly lower than that of acute exercise group at 2h after exercise. Muscle hardness in post-exercise cryotherapy group was significantly lower than that of acute exercise group at three time point (P<0.05).Conclusion:Patella-patellar tendon junction injury model was successfully established by 4-week jumping, hypoxia and angiogenesis, inflammation, increased expression of collagen Ⅲ and increased apoptosis were involved in pathology of patella-patellar tendon junction injury. Long-term post-exercise cryotherapy had no significant interventional effect on patella-patellar tendon junction injury. Post-exercies cryotherapy can suppress PPTJ inflammation and relieve pain, and have a certain role on decreasing muscle hardness.