[A study on proliferation of chondrocyte in callus during second fracture healing].

OBJECTIVE

To understand the regulation of chondrocyte proliferation in callus.

METHODS

The histological structure of callus was observed and the percent of positive cells of Cylin D3, Cyclin E, Cyclin A, PCNA and BrdU in callus of 20 male SD rats were caculated in the fracture healing model by HE staining and immunohistochemical staining at 1, 2, 3 and 4 weeks after fracture.

RESULTS

The callus under light microscope could be divided into four zones: resting zone(RZ), proliferating zone(PZ), mature zone(MZ) and hypertrophic zone(HZ). The arrangement of chondrocytes in callus was irregular and the boundary between the neighboring zones not as clear as on growth plate. The findings indicated that the proliferation and differentiation of the cells in cambium layer of periosteum and RZ played an important role during fracture healing in the first week; the proliferation of chondrocytes in PZ was very active in the second week, meanwhile the cells in cambium layer became quiet; the proliferating activity of chondrocytes in all these zones became declining and the chondrocytes came to be mature and hypertrophic gradually in the fourth week.

CONCLUSION

The proliferating cells in the early stage of fracture healing should have supplied enough chondrocytes, after that time these cells would no longer proliferate; the skeletal repair would be carried out and be accompanied with the proceeding proliferation and differentiation of chondrocytes. After all, the proliferation of chondrocytes in callus is closely related to skeletal repair. Additional characters and elucidation of fracture healing will lay the foundation of subsequent studies aimed at identifying mechanisms for skeletal repair.