Abstract:

BACKGROUND: Construction of bone-tendon junction is similar to endochondral ossification, and the constructed ligament would play its role only a direct tendon-to-bone enthesis regenerates. Recombinant human bone morphogenetic protein-2 (rhBMP-2) can induce undifferentiated mesenchymal cells, fibroblasts, myoblasts and bone marrow stromal cells differentiate into bonelines cells.   
OBJECTIVE: To evaluate the influence of the rhBMP-2 and post-operative immobilization on the entheses reconstruction in rabbits.
METHODS: New Zealand white rabbits were allocated averagely to 3 groups. Totally 20 µL rhBMP-2 solution was injected into the tendon at the point of the entry of bone tunnel in the rhBMP-2 short period immobilization and rhBMP-2 long period immobilization groups. Post-operatively, the operated limb was immobilized by plaster for 1 week in the rhBMP-2 short period immobilization group, and 8 weeks in rhBMP-2 long period immobilization and model groups. The expression of type Ⅰ, Ⅱ collagen, bone alkaline phosphatase (ALP) and osteocalcin (OCN) were examined by immnunohistochemistry and RT-PCR. 
RESULTS AND CONCLUSION: rhBMP-2 could increase the expressions of type Ⅰ collagen, bone ALP and osteocalcin with time prolonged. The expression of type Ⅱ collagen reached a peak at 4 weeks after operation, and then slightly decreased after 8 weeks. However, rhBMP-2 had no significant effect on type Ⅰ collagen mRNA expression, but increased the mRNA expression of type Ⅱ collagen, bone ALP and osteocalcin (P < 0.05), which could be obtained by reducing immobilization duration (P < 0.05). rhBMP-2 not only could upgrade the expression of type Ⅰ, Ⅱ collagen, bone ALP and osteocalcin, but also able to induce the ectopic endochondral ossification in tendon, thus, it makes possible that the entheses healed in the classic anatomical way. By the way, long period immobilization of operated limb has a negative effect on the entheses reconstruction.