Failed digital nerve reconstruction by foreign body reaction to Neurolac® nerve conduit

We read with great interest the recent excellent report by Dr. Meek and Dr. Den Dunnen evaluating the shortterm effects of porous Neurolac nerve conduits to bridge sciatic nerve gap of 10 mm in male Black Hooded rats. They assumed that the use of semipermeable conduits allows the exchange of metabolites through the lumen wall, possibly improve the regeneration process, and allow tissue to grow into the tube wall to form an extra tissue sheath to prevent collapse during nerve regeneration. The clinical results showed a combination of automutilation and flexion contractures in the operated limbs of the rats and lack of nerve function improving over time. Very fast degradation of the porous DL-lactide-e-caprolactone conduits with swelling, fragmentation, and a severe foreign body reaction, hampering the nerve regeneration, could be observed at light-microscopical analysis. The given explanation was that the porosity of the wall of these nerve guides results in an enlarged surface area for hydrolysis that favor a fast degradation of these conduits. Although the wall was made porous, the swelling was so severe that the lumen was blocked and nerve regeneration through the nerve guide was impossible. After a short personal series of four patients with poor results in digital nerve reconstruction in the hand with Neurolac nerve conduits, we have found similar histopathological lesions to those described by Meek and Den Dunnen in a 17-year-old girl, who sustained a painful posttraumatic neuroma in the ulnar collateral nerve of the right thumb. After neuroma resection, the nerve defect was reconstructed with poly DL-lactide-e-caprolactone nerve guide (Fig. 1A). Four months postoperatively, the pain in the volar side of the thumb recurred without sensibility improving. Three months later, the patient asked for revision surgery. At the operation, we observed the degeneration of the nerve guide reconstruction segment (Fig. 1B). It was removed and sent for histopathological study. The new nerve defect was bridged with a posterior interosseous nerve graft. The biopsy showed next to the proximal stump of nerve, which conserved Schwann cells (S-100 protein positives) (Fig. 2A), a severe granulomatous foreign body reaction-type inflammatory response compounds by histiocytes (CD68 positives) (Fig. 2B) with scatter multinucleated cells and widespread necrosis that prevented nerve regeneration. The presence of plasma cells and lymphocyte infiltrate focus together developed of intervened incipient fibrosis between nerve fiber and granulomatous reaction also was evident (Fig. 2C). This experimental study and our clinical experience made us think about human biocompatibility of the material. The use of biodegradable synthetic nerve conduits for the reconstruction of segmental nerve defects has been extensively reported in both animal and human studies. In vitro studies concluded that poly DL-lactide-e-caprolactone nerve guides are biocompatible and show good in vitro degradation characteristics. There are published animal and prospective clinical studies concluding that the Neurolac nerve guides are suitable for the repair of transected peripheral nerves, even they seem to yield better results than collagen and polyglycolic acid conduits. Nevertheless, clinical results are still controversial. Ekholm et al. found that e-caprolactone-lactide copolymer in paste form induces a severe inflammatory reaction *Correspondence to: Pedro Hernández-Cortés, M.D., Ph.D., Rector Marin Ocete, 10, Granada 18014, Spain. E-mail: hdezcp@hotmail.com Received 11 October 2009; Accepted 20 October 2009 Published online 16December 2009 inWiley InterScience (www.interscience.wiley. com). DOI 10.1002/micr.20730