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Histomorphometric Analysis of Facial Nerve Regeneration through Cross-face Nerve Grafts in Facial Reanimation Surgery
Eva Placheta; Chieh-Han John Tzou; Igor Pona; Manfred Frey Division of Plastic and Reconstructive Surgery, Medical University of Vienna, Vienna, Austria
Introduction: Facial palsy leads to functional and aesthetic impairments. An option to emotionally reanimate the paralyzed face is the use of cross-face nerve grafts. These grafts guide healthy facial nerve axons to innervate the paralyzed face, by innervating the denervated mimic facial muscle directly (one-stage procedure) or power a free muscle transplant (two-stage procedure). Biopsies of the donor nerve (healthy facial nerve), the autografts and the recipient branches were harvested for histomorphometric analysis.
Materials and Methods: From 2007 to 2013, 376 nerve biopsies of 84 patients, who underwent cross-face nerve grafting alone, or combined with free gracilis muscle transplantation, were harvested. 75% of patients presented with total and 25% with partial facial palsy. 57% of facial nerve deficits were complete and 43% incomplete. The most common etiologies of the facial palsy were iatrogenic/postoperative (45%), developmental (31%) and idiopathic (9.5%). Biopsies from the cross-face nerve grafting procedure (stage 1) were available in 72 patients and from the free muscle transplantation (stage 2) in 31 patients.
Nerve biopsies were fixed in a 2.5% glutaraldehyde solution, postfixed with 2% osmium tetroxide and embedded in epoxy resin. For histomorphometric analysis, the samples were assessed with a semiautomatic image-analysis system.
Statistic analysis was performed using descriptive analysis, non-parametric tests and Spearman rank coefficient. The two-sided alpha was set at 5%.
Results: The mean axon counts of the buccal facial nerve branch (smile) were 1826.23 (SD: 1497.7) and 576.5 (SD: 341.0) for the zygomatic branch (eye closure). The mean axon count of the sural nerve used as cross-face nerve graft on the donor side was 4575.5 (SD: 1993.8). The mean number of myelinated axons at the distal end of the cross-face nerve graft (stage 2) which innervated the free gracilis muscle from the buccal facial nerve branch was 806.6 (SD: 1348.733) and 175 (SD: 173.0) from the zygomatic branch. Nerve biopsies harvested at both stages, showed that 46% of axons of the buccal facial nerve branch (smile) and 33% of the zygomatic branch (eye closure) reached the free gracilis muscle. Patient characteristic did not significantly correlate with the axon counts.
Conclusion: Objective histomorphometric analysis of the buccal and zygomatic facial branches revealed that ~50% and ~30% of axons reach the distal end of cross-face nerve grafts for the reanimation the paralyzed face with free gracilis muscle transplants.
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