Central and peripheral adaptation after nerve repair with a synthetic biocompatible adhesive

Sammanfattning: The epineural repair technique is currently the accepted standard for peripheral nerve repair. However, due to the demanding nature of this method, it is not uncommon to delay or even omit action, especially in situations which are associated with extensive traumatic injuries. Some of these situations may involve natural disasters, (traffic) accidents, or times of war. Consequently, there is a need for a complementary surgical technique that offers a rapid and reliable primary repair of transected peripheral nerves. Suggestions for techniques using a biocompatible adhesive have been proposed to meet the need. An adhesive would need to have certain qualities such as being simple to apply, having good binding strength with the ability to adhere in a moist environment and being biodegradable in nature and compatible with tissue. In this research, our aim was to create an experimental model that evaluates peripheral nerve transection and repair with a synthetic adhesive and thereafter to compare the results with conventional microsuturing. We also compared two different synthetic adhesives with regard to the cytotoxic effect of a human neuroblastoma cell line. In Studies I, II, and IV unilateral sciatic nerve transections were performed on rats. The nerve endings were readapted microsurgically with cyanoacrylate or epineural sutures. Local tissue showed an increased accumulation of ED-1-immunoreactive macrophages on both sides of the repair site. Neurofilament labelling was less pronounced distal to the repair site seven days after reparation with cyanoacrylate compared with sutures. After six months, when reinnervation had been completed, we examined the tibial branch to the lateral gastrocnemius muscle and the caudal sural cutaneous nerve, in both cases electrophysiologically, as well as morphologically. Functional reinnervation of motor and sensory nerves was observed in both groups. This was shown by equivalent recovery of motor and sensory conduction velocities, as well as motor nerve action potentials. Histological examination showed no significant difference with regard to the mean diameter, fibre density, or the number of regenerated myelinated motor and sensory axons distal to the repair site. The difference in ED-1-immunoreactivity on each side of the repair site was less noticeable. Using the cholera toxin B technique of retrograde axonal tracing over the repair seam, the morphology, the number and the three-dimensional location of alpha-motoneurons innervating the lateral gastrocnemius muscle were evaluated and related to the recorded wet muscle weight. Regardless of which repair method was used, the redistribution of the alpha-motoneuron pool had increased, was disorganised, and was scattered throughout a larger volume of the spinal cord grey matter. The synaptic coverage had decreased and the muscle weight was reduced. In Study III the cytotoxic effect of ethyl-cyanoacrylate was examined on a human neuroblastoma cell line (SH-SY5Y) and compared with the effects of butylcyanoacrylate (Histoacryl®), commonly used for skin closure. Both were applied to confluent SH-SY5Y cultures. The cultures were photographed and analysed digitally. At corresponding intervals, cell death was quantified using a 51Cr release assay. In cultures exposed to either of the two adhesives, cell death was observed predominantly in conjunction with the adhesive causing a halo devoid of cells, which diminished over time. At the 28-day mark, cells had reached the margin of the adhesive in the ethylcyanoacrylate group. The surviving cells showed neurodegenerative properties up to three days post exposure. The cell death, indicated by the 51Cr assay, rapidly decreased during the first 14 days. No significant differences were found between the adhesives. Conclusions: Anastomosis of a transected peripheral nerve with ethyl-cyanoacrylate adhesive supports morphological and functional recovery, a recovery which is comparable to that of conventional epineural sutures. Ethyl-cyanoacrylate causes a transient cytotoxicity, which appears to induce an increased local inflammatory reaction, leading the way to accelerated Wallerian degeneration.. Ethyl-cyanoacrylate does not have any negative influence on the selectivity of motor reinnervation following nerve transection and repair compared to that following conventional microsuturing. This method could therefore offer benefits over conventional sutures in the reconstruction of peripheral nerves.