Induction of facial muscle neurotization by temporalis muscle transposition: Literature review and animal model evaluation using horseradish peroxidase uptake

Objective: To study the concept of facial muscle reinnervation from the tri geminal pathway following facial nerve paralysis. Design and Methods: We studied this phenomenon in an animal model using the neuronal marker, horseradish peroxidase (HRP). The temporalis transpositio n procedure was performed at varying intervals post facial nerve transectio n. To evaluate the trigeminal-facial reinnervation process and its timing, the zygomaricus major muscle was injected with HRP at varied periods after temporalis transposition, and histologic sections of the brainstem nuclei w ere examined for the final location of the MRP. Results: The presence of HRP in the trigeminal nucleus provided evidence of trigeminal-facial neurotization in those animals that underwent temporalis transposition up to 2 months following facial denervation and in which the HRP injection was performed 4 months after temporalis transposition. Conclusions: The findings of our pilot study are strongly supportive of the trigeminal-facial neurotization hypothesis in those animals that underwent temporalis transposition up to 2 months post facial denervation and in whi ch 4 months were allowed thereafter for adequate neurite ingrowth and neuro tization to occur. This suggests that the neurotrophic signals are greatest up to 2 months post denervation and denotes the optimal time for performan ce of reconstructive procedures. Future studies with a larger number of ani mals in each group will be necessary to ensure more potent statistical sign ificance and to augment our experimental evidence that trigeminal-facial cr ossover does occur and can be used as an adjunctive concept to maximize ear ly rehabilitation of the paralyzed face.