Axonal Regeneration In Autologous Grafts: Does A Single-Stage Muscle Transfer Improve Functional Outcomes?
Scott R. Echternacht, BA1,2, Miranda A. Chacon, BS2,3, Michael F. Catanzaro, MD2, Adriaan O. Grobbelaar, MB, ChB, MMed, FCS4,5, Jonathan I. Leckenby, MD, PhD, MRCS2,4.
1University of Rochester School of Medicine and Dentistry, Rochester, NY, USA, 2Division of Plastic Surgery, University of Rochester Medical Center, Rochester, NY, USA, 3Geisinger Commonwealth School of Medicine, Scranton, PA, USA, 4Department of Plastic and Reconstructive Surgery, The Royal Free Hospital, London, United Kingdom, 5Division of Surgery and Interventional Science, University College London, London, United Kingdom.
Facial nerve palsy affects 27-133 people per 100,000 per year. The current optimal surgery for unilateral facial paralysis is a two-stage procedure: the first being a cross facial nerve graft (CFNG) from the active to the paralysed side of the face, and the second, a free vascularised muscle transfer to the paralysed side with attachment of the transposed muscle’s nerve to the CFNG. This permits reanimation of the face in response to emotion, as opposed to the use of an alternative donor nerve which requires extensive relearning to achieve little, if any, emotional response. However, only 60% of patients obtain an excellent result. This study sought to investigate the cause for poor axonal regeneration.
A prospective study was conducted in three phases. Functional outcome measures were combined with histological analysis of axon counts obtained using serial section electron microscopy.
First, 15 patients underwent a two-stage CFNG. Biopsies could only be obtained from the donor nerve and the distal end of the CFNG without negatively impacting outcomes.
Second, a facial nerve mouse model was developed using the posterior auricular nerve as the donor. 80 6-week-old female C57BL6 mice were divided into two groups; half had the nerve transected and directly repaired (DNR group), and the other half had the nerve transected and repaired using an interposed peroneal nerve graft (NGr group).
Third, 10 patients underwent a single-stage procedure utilizing a vascularised latissimus dorsi muscle. The nerve was transplanted from the paralysed side of the face to be coapted to a buccal ‘donor’ nerve.
The functional eFACE score of the 15 patients significantly improved from 44 (32-56) to 78 (63-97) at two-years follow-up. At the first stage, the mean axonal count of the buccal ‘donor’ nerve was 639 (408-1208). At the second stage, the mean axonal count of the CFNG was 309 (76-784); only 48% of the original axons regenerated across the first neurorrhaphy.
At post-operative week 48, the DNR group had significantly better nerve function as measured by recovery of ear movement than the NGr group (76% vs 30%). There was no difference in axonal counts of the donor nerve between the groups. In the DNR group, 79% of axons successfully regenerated across the neurorrhaphy. In the NGr group, the ability of axons to successfully regenerate across a neurorrhaphy was significantly worse (61% and 52%) with only 32% of the original axonal count being available for reinnervation.
The functional eFACE score of the 10 patients significantly improved from 41 (35-51) to 89 (72-96) at two-years follow-up; these scores were significantly better than the two-stage patient group. A biopsy of the buccal nerve made prior to coaptation (702, 337-1154) confirmed there was no significant difference in axonal counts between the two human groups.
The results conclude that the CFNG is detrimental to axonal regeneration. In order to effect optimal emotional outcome in facial palsy, a single-stage procedure with a muscle that has a nerve able to reach from the paralysed side to the active donor nerve is preferred.
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