METHODS: Eight spinal cord nerve guides were placed in a 5-mm gap in the cords of Sprague-Dawley rats. Gaps were created after microlaminectomy and cord exposure at the T8 level. The dura was then sutured closed around the guide’s tubing for inflow and outflow ports. The injection ports were tunneled subcutaneously and sutured in position for post-operative injection. Rats were subjected to gentle injection of saline beginning 1 week post-operatively to assess guide and port patency. Five sham animals underwent microlaminectomy, cord exposure, removal of a 5-mm gap of spinal cord, and dural closure without guide placement.

RESULTS: The first three animals survived a mean of 68 days (range 57-81 days), until sacrifice due to urinary tract infection. Post-operative care was amended to include antibiotic coverage, increased infection control, and a modified bladder-emptying technique. Of the next 5 animals, 4 survived until planned sacrifice at 90 days; 1 animal exhibited autophagia and was sacrificed at 75 days. All 8 guides and ports remained patent and all rats tolerated injections of saline without exhibiting spinal shock. The 5 sham animals survived for a mean of 11 days (range: 7-14 days) until euthanization after exhibiting signs of spinal shock, exemplified by poor feeding, respiratory distress and obtundation. Post-mortem dissection revealed a regenerated cable that spanned the 5-mm gap in all 8 animals in which a nerve guide was placed. The diameter of this cable was significantly smaller than the native cord, yet histologic sections contained a significant number of axons. The mean axon count in the initial group of experimental animals (n=3) was 4256 + 154 (range 1807-6324). A marked fibrotic reaction was observed exterior to the guide’s lumen; while the regenerated cord was sequestered within the lumen. No regenerated cables were seen in sham animals.

CONCLUSIONS: We have designed a spinal cord nerve guide that spans a 5-mm gap in the spinal cord of the Sprague Dawley rat. This nerve guide employs inflow and outflow ports, which should allow trophic factors to be injected into the lumen of the guide, while sequestering the proximal and distal stumps from the mechanical and possibly biochemical impediment of neurite outgrowth by the reactive gliosis and fibrotic components of the lesion scar. Studies are also underway to assess the functional capacity of these regenerated cables.