Axonal regeneration through peripheral nerve grafts: the effect of proximo-distal orientation

Peripheral nerve transplants are used for the surgical repair of nerve loss. If normally oriented grafts contain branches, regenerating axons may be lost into them, limiting re-innervation and restoration of function in the denervated area. Since axons entering a reversed graft may not be lost in this way, we have investigated whether reverse implantation could enhance the number of axons that reach the distal stump. In young adult rats, a section of sciatic nerve, including one major branch, was removed and reinserted with either the normal or reversed proximo-distal orientation, using microsurgical techniques. After signs of recovery of function, the operated and contralateral unoperated nerves of each animal were fixed and processed for electron microscopy. Regenerated axons were seen to enter branches in normally orientated grafts, and there was substantial loss in the cross-sectional area of the graft distal to the branch termination. Reverse grafts are as well reinnervated by regenerating axons as normally oriented grafts and show a smaller loss in the cross-sectional area, even though the branches of these implants seemed to disappear.