RE-INNERVATION OF FACIAL-NERVE TERRITORY USING A COMPOSITE HYPOGLOSSAL NERVE - MUSCLE AUTOGRAFT - FACIAL-NERVE BRIDGE - AN EXPERIMENTAL-MODEL IN SHEEP

The hypoglossal nerve has been used both entirely and in part to repai r the facial nerve. Using the partial technique it may be difficult to obtain sufficient length and a free interposed graft is then required to extend the hypoglossal element. In six sheep the facial nerve was excised between its emergence from the stylomastoid foramen and its bi furcation in the parotid gland. The hypoglossal nerve was exposed and split longitudinally producing a limb which was reflected towards the distal stump of the facial nerve. This left a gap of 4-5 cm which was bridged with a freeze-thawed coaxially aligned skeletal muscle autogra ft. The sheep were examined at 8 months. Laser doppler blood-flow stud ies showed the blood-flow distal to the graft to be about 25% of that at an equivalent site on the normal side. Peak nerve conduction veloci ties were also reduced on the repaired side but stimulation of the pro ximal hypoglossal nerve was nevertheless capable of causing adequate c ontraction of both facial and tongue muscles. Histological comparison of the repaired facial nerves with equivalent sites on the normal side showed a reduction in mean axon and fibre diameters with normal myeli n sheath thickness for the regenerated axon sizes. All of these featur es are to be expected in a regenerated nerve and are consistent with a good level of recovery of function.