Repair of the mandibular branch of the rat facial nerve through transmedian grafting in one or two stages. Functional evaluation.

A previous study examined the morphological outcome of axonal regeneration in the mandibular branch (ramus marginalis mandibulae) of the rat facial nerve after transmedian nerve grafting in one or two stages. The present study supplements the morphological data with a functional evaluation. Recordings of the force of tetanic muscle contractions elicited through stimulation of the mandibular branch showed that upper and lower lip data obtained from animals grafted in one stage did not differ significantly from control data. However, animals grafted in two stages exhibited significantly lower muscle forces compared to one-stage data and to control data. Electromyographic recordings of the M-response showed multiple prolonged potential fluctuations with subnormal amplitudes in grafted cases. In both groups of grafted rats, the mean voltage amplitudes recorded from the upper lip were weaker than the amplitudes seen at the angle of the mouth or the lower lip. The two-stage cases exhibited the most obvious deficit. In conclusion, the present results show that, with respect to the functional restoration achieved three months after nerve injury, repair through transmedian grafting in one stage gives better results than repair in two stages. This finding, which conforms with previous morphological data, suggests that the one-stage procedure should be considered for clinical use.