Correlation Between Facial Nerve Axonal Load and Age and Its Relevance to Facial Reanimation
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BACKGROUND: Two-stage facial reanimation procedures with a cross-facial nerve graft often have unsatisfactory results in the older patient. Although the cause of result variability is likely multifactorial, some studies suggest that increased donor nerve axonal load improves function of a free muscle transfer after a crossface nerve graft. This study attempts to characterize the relationship between age and facial nerve (donor) axonal load. METHODS: 63 fresh, cadaveric heads were dissected to expose the facial nerve. For each hemi-face, two facial nerve samples were taken: one proximal as the nerve exits the stylomastoid foramen, and one distal at the buccal branch (at a point 1cm proximal to the anterior parotid border). Nerve samples were stained and quantified. Correlation analysis was completed using a Pearson's correlation coefficient. RESULTS: 36 females and 27 males were dissected with an average age of 71 (age range 22-97). At the proximal (r = -.26; p < .01; n=104) and distal (r= -.45; p <.0001; n=114) sampling points, there was a significant negative correlation between age and axonal load. CONCLUSION: As age increases, the axonal load of the facial nerve decreases at the buccal and zygomatic branches approximately 1cm proximal to the anterior parotid border. We previously suggested this location as significant for crossfacial nerve coaptation. These results propose that decreasing axonal load can be a factor in the unsatisfactory outcomes of cross-facial grafting in the aging population. Moreover, this underscores the importance of recruiting more donor axons in attempting to improve facial reanimation in the older patient.