An Experimental Study On The Repair Of Massive Loaded Bone Defects With Compound Frozen Cortical Allograft

Objective: This study compared the effect of repairing massive loaded bone defects in rabbits with frozen cortical allograft dealt with different ways hi an attempt to provide a new approach for the reconstruction of clinical segmental loaded bone defects.Method: Forty New Zealand white rabbits were randomly divided into 5 equal groups (Group A, B, C, D, E), and a 2 cm bone defect was created for each animal in the mid-diaphyses of left femur. Type I absorbable collagen sponge(ACS) and type II recombinant human bone morphogenetic protein(rhBMP-2) were used to treat the allograft. All bone defects were implanted respectively with allograft+rhBMP-2+ACS, allograft+rhBMP-2, allograft+ACS, allograft and autograft. All groups were received SPECT (single photon emission computed tomography) and X-ray test after surgery at 3 weeks interval for observing the metabolism and the healing of allograft and measuring area of callus. All animals received tetracycline (250mg/kg, PO, weekly) for 12 weeks, and the dose was changed into 250mg/kg daily in the last three days before the rabbits were euthanatized. All rabbits were sacrificed after 12 weeks and specimens were taken for mechanical testing. The proximal and distal allograft-host junction and the central part of allograft were made into non-decalcified sections for performing histomorphometric analyses under fluorescent and regular microscope. Histomorphometric parameters included new bone formation rate, bone porosity, osteon radius and pore diameter.Result: Like group E, group A demonstrated better performance of X-ray, greater callus formation, higher maximal bending load, higher new bone formation rate, less bone porosity, larger osteon radius and smaller pore diameter as compared with group B, C, D. Group A and E showed more active metabolism of bone at the third and sixth week, but it became stable at the ninth and twelfth week.Conclusion: The allograft transplantation in combination with rhBMP-2 and ACS is a good measure for the repairing of massive loaded bone defects, which has high anddurable osteoinduction, provides adequate mechanical strength, balances bone formation and resorption and enhances the union of allograft and host bone. At the same time, it is an ideal substitute for autograft transplantation because of their similar efficacy of transplant.