Experimental Research On The Repair Of Massive Bone Defects By Using Vascularized Free Ulna Autograft Compounding Bone Allografts

Traffic accidents and various traumas at peace or wartime cause severe bone and joint injuries resulting in defects in long bones. The repair of massive defect in the long bone long since has been a challenge facing the orthopaedic surgeons. The conventional treatment has been allografting which can provide a structural support to the affected limb, however, failure of the allograft to heal to the host tissue more often than not occurs due to its very low abundance of osteoinductive power. Vascularized autograft also is used in repairing massive defect in long bones with its advantage of rapid healing to the host bone, but with its insufficient strength the graft is prone to fracture during the early rehabilitation period after operation. So the orthopaedic community are working in search of a more effective and safer method for repair of large bone defects, and this is the very purpose of the present study.PartⅠPilot studies of allograft combined with vascularizedautograft in repairing bone defects.Objective Todetermine the appropriate locations for tissue retrieval and defect modeling, suitable approach and operation method, fixation method and grouping of animals, providing a basis for further research. Methods The animals were assigned to a study group and three controls. Study group: allograft combined with vascularized autograft; Empty controls: both ulna and radius absent; transplantation of allograft only; vascularized autogaft only. Operation method: 1,contralateral vascularized autograft and allograft; 2,transposition of ipsilateral vascularized autograft and allograft. Fixation: nine-hole plate, external fixation.Results There was a distinct contrast between the study group and the control, group where allograft alone was used. Method two was safe and easy to perform. Firm fixation could be obtained with the use of external fixator. Conclusions It is advisable to assign the animals who receive the vascularized autograft combined with allograft as the study group and use those who receive allograft alone as the control. As to the operative method and the fixation device, transposition of the ipsilateral vascularized ulna and external fixator for immobilization are preferred to others.PratⅡPreparation of allograftsObjective To design and produce long segments of slotted allografts six cm in length which have decreased antigenicity while retaining their strength. Methods The goats were sacrificed and their radii harvested. The radius bone was stripped of periosteum and other soft tissues, then it was cut into more than six cm long segment according to the predetermined design and slotted along its longitudinal axis with marrow being removed. It was subjected to gradient dehydratin with 25%, 50% and 75% alcohol, defatting at 20℃for 4 hours, rinsed thrice with distilled water. The graft was then treated with Co60 γ-irradiation(20KGy,12hours), precooled at 4℃for 12 hours, and finally stored at -80℃until used. Results The ulnas' maximum diameters were measured at a mean of 0.65-0.75cm, and the radii were slotted along their longitudinal axes by reference to these values, making the autograft fit tightly into the allograft. The graft material was then defatted, irradiated and deep-frozen to further reduce its antigenicity, and its contour and strength had not changed markedly after these treatments. Conclusions A graft suited for ues in this study was thus successfully prepared by serial procedures of modeling and processing of the starting material.PartⅢExperimental research on the repair of massive bone defects by using vascularized free ulna autograft compounding bone allograftsObjective To investgate the effects of repairing massive bone defects after bone tumor resection by using vascularized free ulna compounding bone allografts.Methods Six-month goats were chosen as the experimental animals. A 6.0 cm bone defect in diaphysis and periosteum was made at the shaft of ulna and radius. The defects of the animals in experimental group were filled with ipsilateral vascularized free ulna combined with allograft bone. In the controls, the defects were filled with allografts only. Exteranl fixation instrument and plaster were used to keep the grafts steady. X-ray, micro-CT and histological observation were performed after operation or 12 , 24 weeks post-operationly. Results Plenty of new bone were found in the group of experimental group and the defects were completely repaired by the grafts at weeks 24. The healing rate of bone defects were 12/12 by X-ray. On the contrary, no evidense of bone repairing or repairing deformity were found in the control group. After the constrution of Micro-CT, the proximal and distal end of the defects were repaired completely and numorous new bone were formed between the implated allograft and vascularized autografts in the experimental group. Moreover, the defects of allografts were filled with new bone and medullary cavity were formed. The bone mineral density of allografts bone in the control group were declined and obvious bone resorption were found. The new bone formation in experimental group was obviously more than that of control group. Creeping substitution took place not only in the proximal and distal ends but also in the middle of the bone defects in the experimental group by histological investigation. Conclusion With combined use of allograft andvascularized autograft,we produced extensive and profuse new bone formation that extended from the distal and proximal end of the graft to its middle part of the shaft, thus accelerating creeping substitution of the allograft. Bone defects as long as more than six cm have been successfully repaired.In the present study we designed a plan for animal experiments through a preliminary pilot study,and prepared useful allografts from goats. We elected to use a composite graft material that consists of an allograft and a vascularized autograft. The combined use of the two has theoretical advantages over any of them when used alone.In this way we have successfully repaired massive defects in long bones up to six cm long, thus providing scientific basis for its possible clinical ues in suitable cases.