The Effection Of Different Cortical Bone Contents Of Allografts On Impaction Bone Grafting:a Rabbit Animal Experiment

Objective:To explore the different cortical bone contents of allografts to the affection of impaction bone grafting,we compare general observation,X-ray radiograph,and HE staining of three allografts in different periods postoperatively.Moreover,we compare micro-CT data of three allografts in different periods to provide experimental basis for quantitative criteria of bone graft in clinical operations.Methods:This experiment is performed on fifty-five healthy New Zealand White rabbits.All the rabbits weight 2.5-3.0 kg,aged between 10 weeks and 12 weeks.Ten rabbits are treated as donors to provide cancellous and cortical bone allografts.The allografts are weighted and mached as three standards based on cortical bone contents which are 0%,25%and 50%,respectively.The residual forty-five New Zealand White rabbits are completely randomly divided into A,B,C three groups(n=15).Column bone defect is constructed by drilling at the medial femur condyle for each rabbit both legs(diameter=7mm,depth=9mm).Group A:the bone defect is filled with cancellous bone allografts.Group B:the bone defect is filled with 25%cortical bone and 75%cancellous bone allografts.Group C:the bone defect is filled with 50%cortical bone and 50%cancellous bone allografts.Each group of rabbits are euthanized at 4 weeks,8 weeks,and 12 weeks postoperatively.In each group,five rabbits are euthanized at each period.Every rabbits is examined by general observation,X-ray radiography of knee,Micro-CT scaning and HE staining.The general status and wound healing are observed by general observation.The state of bone absorption,new bone trabecula formation and bone-bone grafting interface are observed by X-ray radiography.The mineral substance data and stereology data were obtained by Micro-CT scaning.The coutinuity of bone grafting,the fiber formation,new bone trabecula and the amount of osteocyte and osteoblast are examined by HE staining.Results:Of all the rabbits,one died from anesthetic accident two from diarrhea and one from infection.All the died rabbits were supplied.Histological observation:At 4 weeks postoperatively,we found plenty of atrophic and necrotic trabecular surrounded by large number of proliferous fibrous tissue and fat necrosis vacuoles in the centre of the allograft in three groups.But the number of proliferous is lager in group A and the number of osteoclast is larger in group C.At 8 weeks postoperatively,a large number of osteoblasts are observed surrounding the the new trabecular.Partial allografts trabecula atrophy and be absorbed in the central part.In group B:plenty of osteoclast were on the allograft trabecula surface.A small amount of new trabecula formed.In group C:a little residual cortical bone pieces were surrounded by osteoclasts.At 12 weeks postoeratively,in group A and B,new trabecular was significant proliferation surrounding by reactive new trabecula with numerous osteocyte.In group C,a small amount of trabecular was formed.The new trabecular is thinner than anther two groups’ and the allograft trabecular necrosis is still ongoing.Micro-CT scanning observation:(1)mineral substance parameter:At 8 weeks postoperatively,there are significant differences between group A and group B,C in BV/TV parameter(P=0.001).At 12 weeks postoperatively,there are significant differences between group A,B and Group C in BV/TV parameter(P=0.016),The BMD of group C is larger than group A,B(P=0.029).The TMD of three groups are similar(P=0.600).(2)stereology parameters:At 12 weeks postoperatively The Tb.N of three groups are similar(P=0.210).But the Tb.Sp of group C is larger than group A,B(P=0.000).The trabecular of group C is obviously disorder and the Tb.Th of the group C is thinner than group A,B(P=0.001).Conclusion:(1)All of three allograft are effective to restore the bone defects.Cortical bone delays the bone healing of allograft.(2)The group of pure cancellous bone and the group of 25%cortical bone have the similar outcome at 12 weeks postoperatively.But the group of 50%cortical bone needs more than 12 weeks to heal.(3)The structure of group of 25%and 50%cortical bone are more unstable at 8 weeks postoperatively than any other peroids.