Experimental Study Of Adaptive Remodeling Of Gastrocnemius During Distraction Osteogenesis Of Rabbit Tibia

Background:During recent 30 years, many clinical and basic researches have been done in distraction osteogenesis. But most of them are concentrated on the principles and acceleration factors of bone formation patterns and clinical application. Less research focuses on changes of surrounding tissues caused by distraction osteogenesis. During the process of distraction osteogenesis, peripheral soft tissues are distracted at the same time, so the surrounding soft tissues such as nerves, vessels, muscles and joints are often injuried. Recently numbers of soft tissue problems are concerned. In the 1980s, Illizarov himself had researched and writen some papers about these problems. In 1990, Paley pointed out that the prominent problem in DO is about muscle but not bone. In recent years, the researches about soft tissue problem were increasingly deepened, especially about skeletal muscles.Objective:To observe the structural changes of gastrocnemius and changes of IGF-1 expresssion during rabbit tibia distraction osteogenesis, so as to understand the ability of adaptive remodeling and change rule of gastrocnemius and discuss the remodeling mechanism.Method:Healthy Japan rabbits were performed by upper one-third tibia osteotomy of right hind limb and conducted by unilateral external distractor (distract 0.5mm for each time, twice per day for 10 days after a 7-day lag phase postoperation). Applying the ordinary X-ray is to know growth condition of callus at osteotomy site during distraction and consolidation periods. Fourty-two animals were divided into five experimental groups and one control group randomly. The control group animals were conducted external distractor as the experimental groups but not to be distracted. The animals were killed at the different time. To observe the histological morphology and ultrastructure changes at each consolidation time point by means of light microscope (HE staining) and transmission electron microscopy. The extended gastrocnemius of different groups were performed immunohistochemi-cal staining to determine IGF-1 expression during different time.Result:1. Establish the animal models successively. It can be seen by X-ray that callus images gradually changed clearly following the consolidation period, the amount of callus increased comparing with the previous callus images, the cortical bone combined, the medullary cavity appeared, clearly boundary between the cortical bone and medullary cavity. At last, the callus union is strong, good alignment of prolonged limb, no deformity union.2. Distracting tibia induces the injury of gastrocnemius, but gastrocnemius can repair by itself during consolidation period. The structural changes were observed by light microscope including the muscle fibres' degradation, muscle plasma crumbling degeneration, muscle nuclei internalization; some changes were observed by transmission electron microscopy including myofibrils atrophy and disordered arrange, swelled mitochondrion, muscle nuclei internalization. During the consolidation period, muscle repaired gradually itself, until the late stage of consolidation period (8 weeks),the structure of gastrocnemius returns normal structure.3. The expression of IGF-1 were different during the progress of tibia distraction osteogenesis. The IGF-1 expression of control group was negative; at consolidation 0 day the expression of IGF-1 was strong positive; at consolidation 7 days was also active, but less than the group of consolidation 0 day; from the consolidation 14 days, the expression of IGF-1 began decline; at the consolidation 14 days, the expression of IGF-1 further decline, at the consolidation 56 days, the expression of IGF-1 was the same as the control group.Conclusion:1. Rabbit is an optimal option for limb lengthening animal model. X-ray is a traditional examination way to detect the new bone formation in different lengthening stages. The rabbit limb lengthening model were established successfully. This model can be applied to the following experiments entirely and can acquired the precise data.2. During slow limb lengthening, the subclinical peripheral muscle injury is reversible. The natural repair of the injuried muscle has begun as soon as the muscle was injuried.3. During the process of tibia distraction osteogenesis, the rule of expression changes of IGF-1 was in accordance with the rule of structure changes of gastrocnemius. This result may cues that IGF-1 mediates the functional remodeling of gastrocnemius.