| Background: Limb lengthening technology which applies distraction osteogenesis principle is one of the most effective strategies for treating limb shortening deformity.Many complications are involved in distraction osteogenesis, such as muscle contracture, joint stiffness, injury of peripheral nerves and blood vessels caused by traction. Paley et al proposed that the biggest challenge of limb lengthening is the protection of skeletal muscle, not the bone. Seldom study is available in the basic study field that the injury of muscle caused by bone extension. The functional protection of skeletal muscle is the main factor for performing bone extension successfully.Objective: The present study employed the single arm external fixation to established rabbit tibia lengthening model. Observe the histological changes of extended gastrocnemius in different length proportion with every mineralization point and discuss the bearing capacity of skeletal muscle extended,. Research the expression change of the force growth factor(MGF),Pax7 and myod and explore the molecular mechanism of adaptive remodeling of the gastrocnemius.Methods: Adult Japanese rabbits were used in the present study. They were randomly divided into experimental and control groups. The control group was only performed osteotomy without bone extension, the muscle samples were harvested after 1 week postoperation. According to extension length, the experimental groups were divided into prolong 10% of original tibia length, 20% and 30% groups. Based on the mineralization points, 3 groups were subdivided into consolidation 0d(prolong stop day, M0), mineralization 7d(M7), mineralization 14d(M14), mineralization 28d(M28), mineralization 56d(M56). The gastrocnemius was harvested in every time point and fixed, paraffin embedded, cut into slices. The HE staining and immunohistochemical staining were conducted to observe the histology changes of gastrocnemius and the expression of MGF,Pax7 and myod. The positive areas were performed the image analysis. Summarize the data change rule.Results: 1.All animal surgeries were performed successfully and precise obtained the experimental material because of optimize of the animal model preparative technique.According to the X-ray and limb appearance, the tibia extension length is less than20%, the amounts of callus decreased relative in the same mineralization period following the increase of the bone extension. At the same extension length, the callus showed gradually formatting and the callus amounts increased were observed with the mineralization increase. But when extension is more than 30% of its original length, the callus formatting is very slow and could not achiever the successful bone healing.2. In extension 10% and 20% groups, prolonged gastrocnemius showed obvious injury change in early stage, the degree of injury is aggravated along with the increase of extension length. In later period, the muscles appeared adaptive repair with normal myofiber structures. But in extend 30% group, gastrocnemius undergone maxlength pulling and showed the most serious damage and could not be repaired.3. Both MGF,Pax7 and Myod expressional level in gastrocnemius showed different and with certain law in different mineralization period and extension length of tibia.In the control group, MGF,Pax7 and Myod expression were negative or weakly positive. Following the tibia lengthening, MGF and Pax-7 expression showed strong positive in M0, it is still positive but with decrease in M7, the expression showed weakly positive or negative in M14 and M28, until M56 the expression is the same as the control group; Myod expressed negative in M0, the expression showed positive in M7, and the expression of TGF-β1 showed the highest level at M14, after that the expression level gradually decreased and showed weakly positive at M28; at M56,compared with the control group, the expression was no significant difference.Conclusion:1. Animal models updated carried effective experimental results. Bone lengthening must have a certain limit. Lengthening success rate is low if over the limit.2. Muscle injury caused by bone traction is transient and reversible under the appropriate bone extension length and slowly distracted rate. Damaged gastrocnemius was self-repaired with the development of the consolidation period. However, the irreversible injury will appear if 30% extension length occurred.3. The expression of MGF,Pax7 and Myod showed different results and with specific express peak during DO. Later period, they are all recover to the level of control group. The present results suggested the cellular factors play active roles in the process of muscle damage and recovery. |
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