Treatment Of Rabbit Femoral Head Necrosis Model By Tissue Engineering Bone: An Experimental Study

[Objective]To study the procedure of tissue engineering bone (BCBB /BMP/bFGF/MSCs) and femoral head necrosis(FHN) model of rabbits induced by microwave heating, and the tissue-engineered bone was transplanted to repair the prepared rabbit FHN for evaluate the effect of this tissue engineering bone on the treatment of the FHN in angiogenesis, osteogenesis and the feasibility applied in clinic.[Methods]This study was done in two parts.In part one, a femoral head necrosis model of rabbit was induced by microwave heating. 84 rabbits were randomly divided into three groups according to the microwave temperature and heating time. At six time point after surgery, these specimens were examined by X-ray, histology and MRI to observe the zone of necrosis and repair of femoral head, to determine the optimum microwave temperature and heating time.In part two, the tissue engineering bone was implanted to repair the rabbit femoral head necrosis models. Rabbit femoral head necrosis models were made in 64 femoral heads of 32 rabbits which made by the optimum temperature and time. About 50 percent of femoral head cancellous bone was pared off at 8 weeks after microwave treated. 64 femoral heads in 32 rabbits were randomly divided into four groups, group A implanted by BCBB/BMP/bFGF/MSCs; group B implanted by BCBB/BMP/bFGF; group C implanted by cancellous bone autograft; In group D implanted with nothing. The specimens were harvested separately at 2, 4, 8 and 12 weeks after surgery. 4 femoral heads were examined at each time phase in every group. All specimens were examined to observe the angiogenesis and osteogenesis of the femoral head necrosis of rabbits by gross observation, X-ray, histology, immuhistochemical staining, and to evaluate the repair effect of the tissue-engineered bone (BCBB/BMP/bFGF/MSCs) on FHN.[Results]In part one, in group A the microwave heating at 50℃in 10min could induce partial osteonecrosis of rabbit femoral heads, and this osteonecrosis was self-repaired at 8 weeks. In group B, the microwave heating at 55℃in 10min, there was low density change and cystis degeneration could been seen from x-ray, osteonecrosis and repair occurred at the same time at 4 weeks. But the repair stopped at 8 weeks, 69% femoral heads collapsed at 12 weeks. In group C, the microwave heating at 60℃in 10min, 94% femoral heads collapsed at 12 weeks.In part two, (1) gross observation: Granulation and fibrillar tissue began to proliferate actively in group A and group B at 2 weeks. The boundary between the grafting substance and the host bone was unclear in group C at 12 weeks. Two femoral head collapsed in group D at 8 and 12 weeks respectively.(2) X-ray: The density of the grafting area was higher than the host bone in group A and B, and in group C it was consistent. At the 2nd week, the density was low in group D. At 12 weeks, X-ray grade point showed that it was in group A , B, C superior to that was in group D (p<0．05) , there was no significant difference among group A, B, and C (p>0．05) .(3) Histology: A lot of new bone formed at 8 weeks and BCBB was partly degraded at 12 weeks in group A. In group B: There were many osteoprogenitor cells and osteoblasts and no inflammatory cell infiltration at 4 weeks, and a lot of new bone formed at 8 weeks, and BCBB was partly degraded at 12 weeks, and the chondrocytes and cartilage matrix were abundant. Cancellous bone autograft was absorbed completely at 8 weeks in group C, and the new bone remodeled completely at 12 weeks. There was only a little osteoid tissue formed in group D at 12 weeks. The zone of new bone formation in Group A was more than that in group B (p<0．05) , and there was no significant difference between group A and C (p>0．05) .(4) The amount and zone of new blood vessel: The amount and zone of new blood vessel in group A and B was much at 2, 4 and 8 weeks. There was little in group D . There was no significant difference between group A and B (p>0．05) , but among group A and B, group D, C difference was significant (p<0．05) . This result indicated that bFGF had the effect on angiogenesis.[Conclusions] (1) Femoral head necrosis(FHN) model of rabbits induced by microwave heating was innovated. The microwave heating at 55℃in 10min was the optimum temperature and time for the development of femoral head necrosis model of rabbits. This method has some advantages include the low rate of animal death, the high successful rate, controllable temperature and time, repeatability and operative qualities, and so on. So it is suitable for the repairing study of earlier stage FHN that mimics the clinical situation with trapdoor bone-grafting.(2) The tissue-engineered bone(BCBB/BMP/bFGF/MSCs) showed a good biocompatibility when it was transplanted to repair the rabbit femoral head necrosis model. The BMP can induce MSCs differentiate into osteoprogenitor cells and chondroblast cells. The bFGF can promote differentiate MSCs propagate and stimulate capillary to grow and speed up new bone formation. The tissue-engineered bone (BCBB/BMP/bFGF/MSCs) is superior to BCBB/BMP/bFGF, and it nearly equal to the cancellous bone autograft on repair rabbit femoral head necrosis model. The tissue-engineered bone could be used to repair the FHN patients in clinic.