Selective Cut Of Sensory/ Motor Nerve In Rats During Tibia Fracture Healing Process Experimental Study

Objectives Through the establishment of selective cut of sensory/motor nerve in rats with tibia fracture as animal model, to study the influence of sensory/motor nerve injury during fracture healing and to detect the influence of calcitonin gene-related peptide (CGRP) on osteoprotegerin (OPG)/osteoclast differentiation factor (RANKL) system during fracture healing process, a preliminary study of peripheral nerve injury regulation mechanism during fracture healing.Methods 60 Wistar Rats were divided into 3 groups: motor nerve (ventral root) cut off + tibia fracture group (Anterior rhizotomy group, ART group); sensory nerve (dorsal root) cut off + tibia fracture group (posterior rhizotomy group, PRT group); simple tibia fracture group (sham operated group, SO group); All rats'nerve roots at the exposed side were cut off by the transverse fracture of tibia, all treated by intramedullary nailing. The rats were killed respectively at 7d,14d,21d,28d post surgery, then took the bony calluses from about 0.5cm above and below the fracture site for HE and immunohistochemistry examination.Results The GCRP positive expression level: SO group showed strong positive expression in each time point, in ART group, the result was gradually decreased with time, which is 28d (0.152±0.018)was the lowest. In PRT group, 7d(0.151±0.016) was positive expression, while other time point only showed very low levels of expression. Post op 14d and 21d, there were statistically significant differences in comparisons at SO group, ART group and PRT group (P <0.05). The OPG positive expression level: In the SO group, 7d (0.202±0.025) showed strong positive expression, and then gradually decreased but remain high. In ART group, there were decreased in the expression levels, in which 14d (0.178±0.017) was the lowest. In PRT group, 14d(0.150±0.015)was the lowest. Post-op 14d, there was statistically significant difference between ART group and PRT group,PRT group and SO group respectively(P<0.05). Post-op 21d, there was statistically significant difference between SO group and PRT group, SO group and ART group respectively(P<0.05). The RANKL positive expression level: In SO group, 14d(0.189±0.015)was the highest peak, then gradually decreased. In ART group, 21d (0.188±0.016)was the highest peak, the gradually decreased. In PRT group, each time point showed strong positive expression. Post-op 14d, there was statistically significant difference between PRT group and ART group , PRT group and SO group respectively(P<0.05). Post-op 21d, there was a statistically significant difference between SO group and ART group, SO group and PRT group respectively(P<0.05).Conclusion During fracture healing process, the influence of sensory nerve fibers in fracture healing was significantly higher than motor nerve fibers. CGRP can regulate the OPG/RANKL expression ratio, thus affecting the healing process. Denervation (especially the sensory nerves) causes CGRP regulation on OPG/RANKL expression is reduced, which is not good for fracture healing. Complete innervation is a necessary condition for the normal healing of fractures.