RESUMEN
<p><b>OBJECTIVE</b>To investigate the optimal timing for the repair of persistent incomplete facial paralysis by hypoglossal-facial 'side'-to-side neurorrhaphy in rats.</p><p><b>METHODS</b>A total of 30 adult rats with crushed and bulldog-clamped facial nerve injury were randomly divided into 5 groups (n = 6 each) that were subjected to injury without nerve repair or with immediate repair, 2-week-delayed repair, 4-week-delayed repair, or 8-week-delayed repair. Three months later, the effects of repair in each rat were evaluated by facial symmetry assessment, electrophysiological examination, retrograde labeling, and axon regeneration measurement.</p><p><b>RESULTS</b>At 3 months after injury, the alpha angle significantly increased in the group of rats with 4-week-delayed repair compared with the other four groups. Upon stimulation of the facial nerve or Pre degenerated nerve, the muscle action potentials MAPs were recorded in the whisker pad muscle, and the MAP amplitude and area under the curve in the 4-week-delayed repair group were significantly augmented at 3 months post-injury. Similarly, the number of retrograde-labeled motor neurons in the facial and hypoglossal nuclei was quantified to be significantly greater in the 4-week-delayed repair group than in the other groups, and a large number of regenerated axons was also observed.</p><p><b>CONCLUSION</b>The results of this study demonstrated that hemiHN-FN neurorrhaphy performed 4 weeks after facial nerve injury was most effective in terms of the functional recovery of axonal regeneration and activation of facial muscles.</p>