The Pathogenesis Of Bone Tendon Junction Overuse Injury Induced By Progressive Cyclical Loading

PurposeThe purpose of this study was to evaluate histomorphology, the expression of growth factor, C Reactive Protein and extracellular matrix in the Patella-Patella Tendon Junction (PPTJ) during the early stage of PPTJ overuse injury.MethodForty five female New Zealand rabbits (2.37±0.14kg) were randomly divided into5groups(nine for each group) according to different cumulative cyclical loading. The left rectus femoris muscles were electrically stimulated to contract repetitively for60repetitions/min at30%of peak tetanic force for2h,4h,6h,12h and24h cumulative loading respectively. We randomly choosed, nine contralateral limbs served as controls. The PPTJ were harvested, and sections were stained with H&E, Safrain0, immunostained with antibodies of growth factor, C Reactive Protein and extracellular matrix. We used microscopic imaging system to get the histomorphology measurement and immunostained data. We used SAS6.1.2to make the Statistics. P;<0.05was considered statistically significant.ResultCompared with C, cell density in6h group increased significantly(p<0.01), the fibrocartilage zone increased significantly(p<0.01) in12h and24h group, collagen fiber arrangement in4h,6h,12h and24h group disordered significantly(p<0.01).24h group’s tendon thickness was significantly lower than that of12h group(p<0.05). Positive staining cell density of bFGF in4h group was significantly higher than other groups (p<0.01). Positive staining cell density of CTGF in C group was significantly lower than that of other groups(p<0.01).Positive staining cell density of TGF-β2, PDGF-B in2h group were significantly higher than that of C,6h,12h and24h group(p<0.01). With the increase of cyclical loading, the rate with positive staining of VEGF samples increased significantly(p<0.05), specimens of positive staining BMP-7showed a increase trend of linear(p<0.05). Positive staining cell density of Tenascin-C was significantly quadratic polynomial trend(p<0.05). Positive staining cell density of Collagen Ⅲ in2h and24h was significantly higher than that of C group(p<0.05).Conclusion149759±7285N/kg of body weight cyclical loading can be successfully established PPTJ overuse injury animal model. In the process of overuse injuries occur, there were a sequential pathological changes from disordered arrangement of collagen, cell density increase to fibrocartilage zone broadening. The increase in VEGF expression caused vascular proliferation, the decrease of bFGF lowed PPTJ repair capacity. The decrease expression of TGF-β2reduced ability of tendon to resist pull. high expression of CTGF increased collagen cross-linking. All the expression changes in growth factor above may be the pathogenesis of overuse disease in PPTJ. Increased expression of collagen type Ⅲ and decreased expression of Tenascin-C in extracellular matrix may promote overuse injuries occuring.