A nerve allograft (a graft from a donor) may be used from a living or dead donor. If the allograft is inserted fresh, with all the nerve cells intact, the patient, like an organ recipient, will often have to be on medication that reduces the activity of the immune system. Otherwise, the patient’s immune cells will attack and destroy the foreign tissue of the allograft.
These medications often have severe side effects and increase the risks of serious infections. However, if the allograft is prepared in a way that removes the cells but preserves the connective tissue structure, the immune system will not attack. The connective tissue structure then provides a scaffold for the nerve cells to regenerate and grow beyond the gap.
The method of nerve repair also depends on the type of injury and the amount of nerve that is injured. The simplest method of repair is called direct repair and it works best when the injury is a clean cut through the nerve.
Direct repair re-connects the two nerve ends and uses small suture to re-attach the cut ends of nerve tissue. Direct repair has been in use since the late nineteenth century. In the 1960’s direct repair began to be performed under a microscope. This is the method currently in use for clean cuts through a nerve, where the nerve can be repaired without tension.
Nerve repair becomes much more challenging when a gap exists between the two nerve ends or where there is tension on the nerve repair when the cut ends are approximated. The gap may be caused by the actual injury or may result when the surgeon has to remove injured nerve tissue that did not recover well. In this case, the ends of the nerve cannot be simply re-connected because of the gap between the ends.
If the gap is very small, a nerve conduit (basically a tube) may be placed to connect the ends and guide the growth of the recovering nerve. For a longer gap, a piece of nerve (either from the patient or a donor), called a graft, will need to be inserted to span the gap. A patient’s own sensory nerve, called an autograft (a graft from the patient him/herself), may be used as a graft to re-connect an injured nerve.
The downside to this is that, since a sensation-carrying nerve was cut out and used as a graft, the patient will be left with an area that no longer has sensation. The patient also has a limited amount of nerves that can be used as grafts and the procedure to harvest the graft involves a second surgery site. Alternatively, a nerve allograft (a graft not from the patient) may be used from a donor.
Avance nerve allograft (AxoGen) is a human nerve allograft that is processed to remove cells while preserving the connective tissue structure. The tissue structure of human nerve is retained throughout processing, so recovering nerve is able to regenerate across existing structural elements.
Avance allografts are used in nerve repair to bridge a gap when direct repair is not possible, or when there is tension when the cut ends are approximated. They are available in various lengths and diameters to conform to various gap lengths and injured nerve sizes.