A quantitative morphological comparison of cat lingual nerve repair using epineurial sutures or entubulation

Extracting structural features of rat sciatic nerve using polarization-sensitive spectral domain optical coherence tomography

We present spectral domain polarization-sensitive optical coherence tomography (SD PS-OCT) imaging of peripheral nerves. Structural and polarization-sensitive OCT imaging of uninjured rat sciatic nerves was evaluated both qualitatively and quantitatively. OCT and its functional extension, PS-OCT, were used to image sciatic nerve structure with clear delineation of the nerve boundaries to muscle and adipose tissues. A long-known optical effect, bands of Fontana, was also observed. Postprocessing analysis of these images provided significant quantitative information, such as epineurium thickness, estimates of extinction coefficient and birefringence of nerve and muscle tissue, frequency of bands of Fontana at different stretch levels of nerve, and change in average birefringence of nerve under stretched condition. We demonstrate that PS-OCT combined with regular-intensity OCT (compared with OCT alone) allows for a clearer determination of the inner and outer boundaries of the epineurium and distinction of nerve and muscle based on their birefringence pattern. PS-OCT measurements on normal nerves show that the technique is promising for studies on peripheral nerve injury.

Histomorphometric changes in repaired mouse sciatic nerves are unaffected by the application of a scar-reducing agent

Microsurgical repair of transected peripheral nerves is compromised by the formation of scar tissue and the development of a neuroma, thereby limiting the success of regeneration. The aim of this study was to quantify histomorphometrically the structural changes in neural tissue that result from repair, and determine the effect of mannose-6-phosphate (M6P), a scar-reducing agent previously shown to enhance regeneration. In anaesthetised C57-black-6 mice, the left sciatic nerve was sectioned and repaired using four epineurial sutures. Either 100 μL of 600 mm M6P (five animals) or 100 μL of phosphate-buffered saline (placebo controls, five animals) was injected into and around the nerve repair site. A further group acted as sham-operated controls. After recovery for 6 weeks, the nerve was harvested for analysis using light and electron microscopy. Analysis revealed that when compared with sham controls, myelinated axons had smaller diameters both proximal and distal to the repair. Myelinated axon counts, axonal density and size all decreased across the repair site. There were normal numbers and densities of non-myelinated axons both proximal and distal to the repair. However, there were more Remak bundles distal to the repair site, and fewer non-myelinated axons per Remak bundle. Application of M6P did not affect any of these parameters.

Facial nerve repair with expanded polytetrafluoroethylene and collagen conduits: an experimental study in the rabbit

PURPOSE

This study evaluated autogenous nerve grafts and expanded polytetrafluoroethylene (e-PTFE) and collagen tubes as conduits for the repair of continuity defects in the facial nerve of rabbits.

MATERIALS AND METHODS

The buccal division of 24 facial nerves was isolated, transected, and separated 10 mm. The gap between the 2 nerve ends was then repaired with an autologous nerve graft or an e-PTFE or collagen conduit. Fifteen days and 1, 2, and 4 months after the procedure, the animals were subjected to electrophysiologic tests, killed, and the nerves were removed for histologic examination.

RESULTS

At 15 days postsurgery, no regeneration was observed through the e-PTFE and collagen tubes or across the autologous nerve grafts at the midpoint of the specimens. However, regeneration across the chambers and autologous nerve grafts was seen in the following 4 months, although the number of axons regenerated was small.

CONCLUSIONS

The results of the study indicate that e-PTFE and collagen tubing may be effective in the repair of continuity defects in peripheral nerves. However, further research will be necessary for generalization of this procedure.

A prospective, quantitative study on the clinical outcome of lingual nerve repair

We previously showed in laboratory studies that the most effective method for repair of damaged lingual nerves was by excision of the neuroma, mobilization of the stumps, and direct reapposition with epineurial sutures. We have now undertaken a prospective study in a series of 53 patients treated by this method and have evaluated the outcome by quantifying and comparing the results of tests of sensation before and after operation. The outcome in individual patients was variable. However, pooled data from all patients showed a highly significant improvement in sensation at the final assessment 12 months or more after the repair. The proportion of patients who responded to most or all light touch stimuli increased from 0% to 51% after repair, and the proportion who responded to pin-prick stimuli increased from 34% to 77%. There was no correlation between the final results of any of the tests and the delay before repair. None of the patients regained completely normal sensation and there was no reduction in the number with spontaneous paraesthesia or pain. However, fewer patients tended to bite the tongue by accident and most of them considered the operation worthwhile. These data show that lingual nerve repair is effective in most patients and we suggest that it should be offered to all those who show few signs of spontaneous recovery after injury.

Experimental trigeminal nerve injury

The successful reinnervation of peripheral targets after injury varies with the axonal population of the nerve that is injured and the extent of the dislocation of its central component from the peripheral endoneurial tube. Larger-diameter axons such as those supplying mechanoreceptors recover more readily than narrower axons such as those supplying taste. A complex, bi-directional interaction between lingual epithelium and sprouting nerve results in the redifferentiation of taste buds after denervation. Dentin and the dental pulp provide a strong attraction to sprouting nerves and will become reinnervated from collateral sources if recovery of the original innervation is blocked. The most effective repair technique for transected lingual nerves is one which brings the cut ends together rather than one that provides a temporary bridge. Injuries can result in cell death in the trigeminal ganglion but only if the injury is severe and recovery is prevented. Lesser damage results in chromatolysis and the increased expression of neuropeptides. All nerve injuries bring about changes in the trigeminal nucleus. These occur as changes in receptive field and the incidence of spontaneously active neurons, effects which are consistent with the unmasking of existing afferents. These functional changes are short-lived and reversible. Morphologically, nerve injury results in terminal degeneration in the nuclei and an increased expression of the c-Fos gene and some neuropeptides. Only a chronic constriction injury induces behavioral changes. The adult trigeminal system retains considerable plasticity that permits it to respond successfully to nerve injury. Much remains to be learned about this response, particularly of the trophic factors that control peripheral recovery and the central response to more severe injuries.