| Objective To establish the rabbit model of tibial lengthening using the simple homemade monolateral external fixation.All rabbits are divided into different groups according to different distraction degree and different mineralized time. To observe histopathological changes of meniscus, so as to understand the meniscal organizational structure and histopathological changes under the impact of the tibial lengthening, and to provide a theoretical foundation for the understandings and preventions of knee complications during limb lengthening procedure. Methods Forty healthy white rabbits whose weihgts were 2.5-3.0kg. They were randomly divided into the experimental group and the control group. The rabbits in Group A(control group) just performed osteotomy without tibial lengthening,then they were killed and taken out meniscus before the start of distraction.According to the different distraction degree, the experimental group was divided into three groups, Group B(the rabbits’ tibia were prolonged 1cm,about 10% of the whole length of the tibia), Group C(the rabbits’ tibias were prolonged 2cm), Group D(the rabbits’ tibias were prolonged 3cm). Every group was subdivided into 3 Subgroups based on the mineralized time, including the Subgroup A1,B1,C1(the rabbit were killed at the end of each limb lengthening process immediately);Subgroup A2,B2,C2(the rabbit were killed after 30 days of each limb lengthening process), Subgroup A3,B3,C3(the rabbit were killed after 60 days of each limb lengthening process). The rabbits of experimental group were performed the tibial osteotomy fixed with the homemade monlateral external fixator and began distracted after 6 days of the operation with a rate of 1mm/d. They were killed at the time point when the mineralization process were finished. Before that the X-ray films of distracted limbs should be taken to observe the Axis line of prolonged tibia, the length accuracy, etc.Derived meniscal tissue did HE staining,toluidine blue staining and chondrocyte type Ⅱcollagen immunohistochemical staining to observed the histological morphology changes of chondrocytes in meniscus,the expression of Proteoglycan and type Ⅱ collagen during different mineralization time with different distraction degree. Result 1. The rabbit model established. With the increase of the lengthening, X-ray showed a gradual increased gap between the two bony fragments, and as mineralization period extended, new bone tissue is generated in the gap between the two segments, At last, the callus union was acquired without significant malunion. As the increase of the distraction degree,knee joint space became narrow correspondingly. 2. General appearance: The meniscus of control group showed light blue color, with shiny and smooth surface, normal shape, appearance plump; The meniscal appearances of GroupB and C are similar with that of Group A. The meniscal appearances of Group D showed visible pale, less smooth surface, little deformation of the inside edge. 3. With the increase of distraction distance,more and more meniscal chondrocytes lost their normal shape, cartilage lacuna disappeared gradually, meniscal fibers had disordered arrangement with fiber gap increased, and there were even some fibers repture phenomena occur. Low distraction distance group(1cm and 2cm),with the extension of mineralization period, the recovery of chondrocytes happened quickly,while chondrocytes degeneration of 3cm group is obvious, the recovery appeared slowly.The fiber damage had no significant signs of recovery. 4. Toluidine blue staining and Type Ⅱ collagen immunohistochemistry:At the end of distraction period,each group showed light staining with reduced Stained area;with the extension of the mineralization period,the staining colour became more heavy and Stained area became larger.Group B and C show obvious changes,while the staining colour of Group D was light and didn’t have significant changes. Conclusion 1. Rabbit is an optimal option of limb lengthening animal model. The rabbit limb lengthening model be applied to the following experiments entirely and can acquired the precise data. 2. Different meniscal pathological changes happened during limb lengthening period, Slight limb lengthening(extension<20% limb length), the damage of meniscus is slight. With the Significant extension of limb(extension > 30% limb length), meniscal morphology damages were significant increased. 3. Subclinical knee meniscus damage followed appropriate slow limb lengthening is temporary and reversible, the damage can be repaired by a certain degree of self-regulation; and when the significant extension cause meniscal injury,it is difficult to recovery. |
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