Stress and strain analysis on the anastomosis site sutured with either epineurial or perineurial sutures after simulation of sciatic nerve injury

The magnitude of tensile stress and tensile strain at an anastomosis site under physiological stress is an important factor for the success of anastomosis following suturing in peripheral nerve injury treatment. Sciatic nerves from fresh adult cadavers were used to create models of sciatic nerve injury. The denervated specimens underwent epineurial and perineurial suturing. The elastic modulus （40.96 ＋ 2.59 MPa） and Poisson ratio （0.37 ＋ 0.02） of the normal sciatic nerve were measured by strain electrical measurement. A resistance strain gauge was pasted on the front, back left, and right of the edge of the anastomosis site after suturing. Strain electrical measurement results showed that the stress and strain values of the sciatic nerve following perineurial suturing were lower than those following epineurial suturing. Scanning electron microscopy revealed that the sciatic nerve fibers were disordered following epineurial compared with perineurial suturing. These results indicate that the effect of perineurial suturing in sciatic nerve injury repair is better than that of epineurial suturing.

The reasons for end-to-side coaptation:how does lateral axon sprouting work?

Nerve fibers are attracted by sutureless end-to-side nerve coaptation into the recipient nerve. Opening a window in the epineurium enhances axon attraction and myeliuation. The authors analyze the features of nerve repair by end-to-side coaptation. They highlight the known mechanisms of axon sprouting and different hypotheses of start up signals （presence or absence of an epineurial window, role of Schwann cells, signaling from the distal trunk）. The clinical literature is also presented and differences between experimental and clinical applications are pointed out. The authors propose their point of view and perspectives deriving from recent experimental and clinical experiences.

variation in expression of small ubiquitin-like modifiers in injured sciatic nerve of mice

Small ubiquitin-like modifiers (SUMOs) have been shown to regulate axonal regeneration, signal transduction, neuronal migration, and myelination, by covalently and reversibly attaching to the protein substrates during neuronal cell growth, development, and differentiation. It has not been reported whether SUMOs play a role in peripheral nerve injury and regeneration. To investigate any association between SUMOylation and potential neuroprotective effects during peripheral nerve injury and regeneration, C57/BL mice were randomly divided into sham and experimental groups. The sciatic nerve was exposed only in the sham group. The experimental group underwent neurotomy and epineurial neurorrhaphy. Real-time quantitative polymerase chain reaction and western blot assay results revealed different mRNA and protein expression levels of SUMO1, SUMO2, SUM03 and UBC9 in sciatic nerve tissue (containing both 5 mm of proximal and distal stumps at the injury site) at various time points after injury. Compared with the sham group, protein levels of SUM01 and SUMO2/3 increased in both their covalent and free states after sciatic nerve injury in the experimental group, especially in the covalent state. UBC9 protein levels showed similar changes to those of SUMO1 and SUMO2/3 in the covalent states. Immunohistochemical staining demonstrated that SUMO1 and SUMO2/3 immunopositivities were higher in the experimental group than in the sham group. Our results verified that during the repair of sciatic nerve injury, the mRNA and protein expression of SUMO1, SUMO2, SUMO3 and UBC9 in injured nerve tissues changed in varying patterns and there were clear changes in the expression of SUMO-related proteins. These findings reveal that SUMOs possibly play an important role in the repair of peripheral nerve injury. All animal protocols were approved by the Institutional Animal Care and Use Committee of Tianjin Fifth Central Hospital, China (approval No. TJWZXLL2018041) on November & 2018.

Autologous nerve graft repair of different degrees of sciatic nerve defect:stress and displacement at the anastomosis in a three-dimensional finite element simulation model

In the repair of peripheral nerve injury using autologous or synthetic nerve grafting, the mag- nitude of tensile forces at the anastomosis affects its response to physiological stress and the ultimate success of the treatment. One-dimensional stretching is commonly used to measure changes in tensile stress and strain; however, the accuracy of this simple method is limited. There- fore, in the present study, we established three-dimensional finite element models of sciatic nerve defects repaired by autologous nerve grafts. Using PRO E 5.0 finite element simulation software, we calculated the maximum stress and displacement of an anastomosis under a 5 N load in 10-, 20-, 30-, 40-mm long autologous nerve grafts. We found that maximum displacement increased with graft length, consistent with specimen force. These findings indicate that three-dimensional finite element simulation is a feasible method for analyzing stress and displacement at the anas- tomosis after autologous nerve grafting.