Comparison of effect on nerve recovery underwent oncologic sterilization methods such as extracorporeal irradiation and liquid nitrogen on the rat sciatic autograft nerve model

Comparison of effect on nerve recovery underwent Oncologic Sterilization Methods such as extracorporeal irradiation and liquid nitrogen on the rat sciatic autograft nerve model Introduction – Objective; Tumor contaminated bone, tendon, vascular structures and neural tissue is removed through wide resection in skeletal malignant bone tumors and soft tissue sarcomas. One of methods used in the reconstruction of occurred bone and tendon defects is; extracorporeal (outside the body) irradiation of structures (devitalization of oncological sterilization) and than using these structures as autografts (reimplantation). These autograft preperation method has been used for reconstruction of tendon and bone defects in malign bone and soft tissue tumor patients. The purpose of this study is to reveal success of oncologically sterilized autograft method in nerve defects after wide resection operations ,which is already being used in the reconstruction of bone and tendon defects. Methods: 48 Sprague-Dawley rats ranging from 250 to 300 grams were used in this study . Subjects were divided into three groups as autograft, irradiation and nitrogen group. All rats were operated only on their right sciatic nerve. 10 mm long nerve defect created in the sciatic nerve was reconstructed with autograft obtained from the nerve itself. Group 1 underwent reconstruction with standard nerve autograft. Group 2 underwent reconstruction with devitalized nerve autograft treated through extracorporeal irradiation. Group 3: underwent reconstruction with devitalized auotograft treated through liquid nitrogen. Half of the subjects were evaluated in early stage at 12 weeks and the other half in late stage at 16 weeks . As the final evaluation; EMG, motor strength at the curved table and histomorphologically nerve changes were observed. Results: In spite of both irradiation and liquid nitrogen groups, better motor function values in early and late stage of the autograft group was obtained , however no significant statistical difference was distinguished among these 3 groups. EMG; autograft group exhibited the best latency time , while nitrogen group did the worst , where early period myelinisation process was under focus . There was no difference among 3 groups in the late period. CMAP amplitude assessment was made to detect axonal regeneration . Accordingly ; in early period nitrogen group determined as the worse. In late period autograft group was significantly better, whereas nitrogen and radiotherapy groups were similar. Histological study of myelinated nerve fibers ; the autograft group showed better results in all the assessments than both nitrogen and irradiation groups. According to assessment made in the late period; nitrogen group in the graft segment and irradiation group in distal segment of the graft showed high myelination rates . There was fibrosis in all 3 groups, but fibrosis and apoptotic cell rate in nitrogen group was higher than other groups. Also revascularization rate in irradiation and liquid nitrogen groups were lower than fresh autograft group. Conclusion: Autograft model was determined to be more superior to devitalized nerve autografts prepared with irradiation and liquid nitrogen, in experimental sciatic nerve graft modelling. Besides, devitalized nerve autografts prepared with irradiation and liquid nitrogen has an adverse effect axonal regeneration. Healing potential of nerve autografts prepared with oncologic sterilization methods such as irradiation and liquid nitrogen appears to be lower than normal autografts, however this method is shown to be appliable for nerve defects after tumor surgery. It is impossible to predict clinical results of our experiment performed on rat models. Keywords: extracorporeal devitalization, irradiation, liquid nitrogen, nerve autograft