NERVE GRAFTING
Of all the methods of free nerve grafting the most efficient is the autograft, taken intraoperatively (autotransplantation). Most often cutaneous nerves of little functional importance such as the sural nerve, or mixed nerves such as intercostal nerves or others are used as grafts. Ordinarily the graft is thinner than the recipient nerve. According to the classical method, some segments of the graft are united in the form of a cable and are sutured to the nerve gap by epineural sutures. On this account several pieces must be taken and placed side to side to one another, but so that the common diameter is the same. For instance, if it is necessary to make a transplantation of a 4-mm thick nerve, 4 pieces 2 mm thick must be taken. The cross-section nerve surfaces from which the graft is made are sutured one to another by an epineural suture, which remains in the middle. After that the nerve is sutured according to the general rules, applying microsurgical techniques (Figs. 19-14; 19-15). In delayed reconstruction when nerve grafting is performed, it is important to make motor and sensory alignment at the proximal and distal nerve stumps. The technique that can be used to identify motor and sensory fascicles in the proximal stump includes the use of anatomical clues (surgical identification of fascicles going to specific muscles or cutaneous territories), topography maps, awake stimulation and enzyme staining. It is not possible distally to use wake stimulation or enzyme staining and the surgeon must rely on anatomical dissection aided by anatomical maps to orient motor and sensory fascicular groups. In order to assess in advance which of the skin nerves are convenient for graft material in a given injury of the peripheral nerve, the approximate thickness of the more important nerves must be known beforehand.
According to T. Tarlov's data the average of the thickness of the more important peripheral nerves that need grafting is:
Median nerve at the beginning 4,1 mm
Median nerve at the elbow 3,5 mm
Radial nerve at the beginning 4,3 mm
Ulnar nerve at the beginning 3,8 mm
Ulnar nerve at the wrist 2,5 mm
Sciatic nerve at the middle of the thigh - 8-3 mm
Tibial nerve at popliteal fossa 4,7 mm
Tibial nerve at the ankle 3,5 mm
Peroneal nerve at popliteal fossa 3,6 mm
Femoral nerve at the inguinal region 4,8 mm
Most important nerves, used for grafts
have the following thickness and lengths:
Sural nerve – 25-40 cm length and 2-mm thickness.
Intercostal nerve – 15-20 cm length and 1-2 mm thickness.
Lateral cutaneous nerve of thigh – 15-20 cm length and 2 mm thickness.
Saphenous nerve – 40 cm length and 1 mm thickness.