| Part one:Establishing the model of delayed union after internal fixation surgery with LCP of tibial fracture in rabbitsObjective:To build an experimental model for delayed union of tibial fracture in New Zealand rabbits after locking compression plate fixation,Providing an objective animal experimental basis for the experimental study of fracture delayed union.Methods:Twenty-four mature male New Zealand white rabbits were selected to establish a model of delayed healing of the right tibia fracture,all of them were randomly divided into two groups:the rabbits of control group were subjected to transverse osteotomy at 1 cm below the right tibiofibular syndesmosis,and locking compression plate was internally fixed on the fracture site,Three locking screws at each side of the plate were placed in the locking holes,with protecting the periosteum and bone marrow,and the fracture ends were closely contacted without any spacing.The rabbits of experimental group were underwent transverse osteotomy on the right tibia at the same position.The locking compression plate was used to maintain a gap of 1 mm between the fracture ends,what's more,1 cm of the periosteum at the distal and proximal ends of the fracture line was peeled off,1 cm of bone marrow on each side of the fracture end was removed too.X-ray examination was performed at the time of 2,4,6,8,10,and 12 weeks;at the time points of 4,8,and 12 weeks after operation,the tibial specimens was generally observed,and the HE and safranin fast green staining were used to observe the histomorphology and cartilage formation of callus.Results:X-rays,gross specimens,and histopathological examination showed that the control group achieved bone union at 4 weeks after the fracture;the experimental group reached bone union at about 12 weeks,and there was no case of nonunion in the experimental group.Conclusion:The animal experimental model of fracture delayed union established in this research can not only meet the requirements for prolonging the fracture healing time,but also ensure the final fracture uniting without bone nonunion.It can be considered as a reliable and practical animal experimental model.Lay the foundation for the successful development of subsequent experimental research.Part two:The dynamization of LCP-Biomechanical analysis of micromotion in the fracture site of rabbit tibial shaftObjective:To investigate the effect of different types of screws and screw holes combination methods on locking compression plates(LCP)on the axial micromotion of rabbit tibial shaft fracture site by biomechanical analysis,and to provide experimental basis for the clinical application of LCP dynamization.Methods:Eighteen mature male New Zealand white rabbits were divided into three groups of A,B and C according to the random number table method,with six rabbits in each group,After obtaining the whole fresh right tibial specimens,cut off transversely from the middle,and fixed with LCP,The distal side of the fracture end was fixed with locking screws in locking holes of all the specimens.Locking screws were fixed in locking holes at proximal end in Group A;In group B,common screws were fixed in locking holes at proximal end;While in Group C,common screws were fixed in compression holes at proximal end.All specimens were subjected to a dynamic axial load of 0 to 50 N on a universal test machine,Through the instrument's own system to measure the distance of the micromotion of the fracture site,calculate the axial compression stiffness corresponding to each fixing method,And evaluate above datas.Results:All specimens generated corresponding axial displacement under the axial load.Under an axial load that approximated a body weight(25N),the axial displacement value of the fracture end was(0.101±0.017)mm in group A,(0.164±0.007)mm in group B,and(0.305±0.041)mm in group C;Under the axial load of approximately two body weights(50N),the axial displacement value of the fracture end was(0.218±0.012)mm in group A,(0.285±0.013)mm in group B,and(0.513±0.051)mm in group C.Under the same load,the average axial displacement value of fracture site was C>B>A(P<0.01);The axial stiffness of the fixing device was A>B>C(P<0.01).Conclusion:"Dynamization" of LCP(fixed with common screws or via compression holes)can significantly increase axial micromotion of the fracture end,and the effection is more obvious when combined application of the two;It can reduce the stiffness of the LCP device and provide experimental evidence for fracture healing.Part three:Efficacy observation and preliminary mechanism research on delayed union in rabbit's tibial fracture treated by the dynamization of LCPObjective:Based on the study of the first and second part,to observe the treatment effect by dynamization of LCP on rabbit's tibia fracture delayed union.and to explore the primary mechanism of LCP dynamization promoting fracture healing.Methods:Fifty-four mature male New Zealand white rabbits were selected to establish an experimental model of delayed union of right tibia fractures.All rabbits were divided into three groups randomly.Group A:no special treatment was performed after internal fixation of the tibia fracture;Group B:At the time of 4 weeks after fracture internal fixation,taking "dynamization" on the LCP,that is,the three locking screws at the proximal end were removed,and the holes were re-drilled through the plate compression holes and fixed with common screws;Group C:At the time of 4 weeks after fracture internal fixation,taking "dynamization" on the LCP,and using a syringe needle to drill and grind around the fracture site to perform"freshness".The experimental models of each group were performed x-ray examination of the right tibia at 2,4,6,8,10,and 12 weeks after fracture internal fixation,Lane and Sandhu radiographic scoring was used to evaluate the fracture healing,and recording the time of fracture union.6 rabbits' right tibia specimens were randomly obtained at 6,8,and 12 weeks after fracture internal fixation in each group.Observing the healing of tibial fractures.Three of them were examined by micro-CT analyses.The total volume(TV),bone volume(BV),bone volume fracture(BV/TV),bone surface(BS),trabecular thickness(Tb.Th),trabecular separation(Tb.Sp),trabecular number(Tb.N),bone surface(BS),and bonemineral density(BMD)were measured,and comparing the differences in healing quality of tibia fractures among the three groups.Morphological observations were performed on the other 3 specimens,including HE and saffron solid green staining to observe the morphology of the callus and cartilage formation;the expression of BMP-2,TGF-?1 and VEGF in bone tissue were detected by immunohistochemistry.Rabbit serum samples of each group were collected at the time of preoperative and 2,4,6,8,10,and 12 weeks after surgery,and detected the amount of osteogenic markers(BALP and PINP),osteoclast markers(CTX),and bone calcification markers(TGF-?1).The differences in the above data were compared and evaluated among the three groups.Results:The X-ray scores of groups B and C were higher than those of group A at 2,4,6,and 8 weeks after the second stage surgery(P<0.05),and the fracture healing time was faster than that of group A(P<0.05),but there was no significant statistical difference between group B and group C in the above two indicators.Micro-CT test showed that all the indexes of group B and C were higher than those of group A at 2 and 4 weeks after the second stage surgery(P<0.05).and the three indexes of TV,BV/TV and TB.N in group C were significantly higher than those in group B at 4 weeks(P<0.05).At 8 weeks after the second stage:TV of group B and C are smaller than group A,and group C is smaller than group B too,there are significant statistical differences;In BV/TV,TB.Sp and BMD indicators,the two groups of B and C were higher than group A(P<0.05),and on BV/TV,group C was higher than group B(P<0.05).HE and saffron solid green staining of bone specimens showed that at 2 and 4 weeks after operation of the second stage,the callus tissues and fracture healing process in groups B and C were better than those in group A.Bone tissue immunohistochemical results showed that the expressions of BMP-2,TGF-?1,and VEGF at each time point were higher in the B and C groups than in the A group.And at 4 weeks after the second stage,the three osteogenic factors in group C were higher than those in group B(P<0.05).ELISA tests showed that the serum osteogenic activity markers(BALP,PINP)in the B and C groups were higher than those in the A group in the early period of the second stage,and the BALP level in the group C was significant higher at 2 and 4 weeks after the second stage Compared with group B,The serum levels of TGF-?1 in group B and C were higher than those in group A at 2,4,and 6 weeks after the second stage(P<0.05),and group C was also significant higher than group B at 2 and 4 weeks;The CTX in the group B and C were significantly higher than that of the A group at 2w after the second stage,and were significantly lower than those of the A at 6 and 8weeks after the operation,There was no significant statistical difference between group B and C.Conclusion:LCP "dynamicization" has a greatly positive effect on the delayed union of rabbit tibia fractures,which can accelerate the healing time of fractures,improve the quality of fracture healing,and promote fracture healing.LCP"dynamicization" improved the expression of local osteogenic activity factors during fracture healing,stimulated the differentiation and maturation of osteoblasts and chondrocytes in the epiphyseal tissue,accelerates the formation of new bone,and promotes fracture healing.The effect is more significant when LCP"dynamicization" combined with "broken end freshened". |
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