ABSTRACT
The classic hypoglossal transfer to the facial nerve is invariably followed by complications
caused by tongue atrophy. In 1984, Terzis introduced the “baby-sitter” procedure which
involved a formal cross-facial procedure, in addition to partial neurectomy of the
hypoglossal nerve, and an end-to-side coaptation with the ipsilateral facial nerve.
This reported study provides, for the first time, quantification of the number of
hypoglossal motor fibers needed to successfully restore eye sphincter function, using
an end-to-side coaptation with preservation of the tongue. Thirty adult Sprague-Dawley
rats were divided into six groups: control, denervated, perineurial window, 20 percent
partial neurectomy (PN), 40 percent PN, and 80 percent PN. The procedure involves
interposing a nerve graft (saphenous) between the partially severed XII nerve and
the upper zygomatic branch of the facial nerve. Evaluation of the behavioral data
(blink reflex) revealed good-to-superb return of the blinking mechanism in the 40
percent group, without significant tongue atrophy. Electrophysiologic data in the
40 percent neurectomy group demonstrated superiority to the other groups. Quantitative
axonal morphometry of the coaptation sites and graft, as well as motor end-plates
of the orbicularis oculi muscle and tongue showed the 40 percent partial neurectomy
group to be the optimal group.
