Surgical anatomy of the ovine sural nerve for facial nerve regeneration and reconstruction research

Surgical Training on Ex Vivo Ovine Model in Otolaryngology Head and Neck Surgery: A Comprehensive Review

Background: Nowadays, head and neck surgical approaches need an increased level of anatomical knowledge and practical skills; therefore, the related learning curve is both flat and long. On such procedures, surgeons must decrease operating time as much as possible to reduce the time of general anesthesia and related stress factors for patients. Consequently, little time can be dedicated for training skills of students and young residents in the operating theater. Fresh human cadavers offer the most obvious surrogate for living patients, but they have several limitations, such as cost, availability, and local regulations. Recently, the feasibility of using ex vivo animal models, in particular ovine ones, have been considered as high-fidelity alternatives to cadaveric specimens. Methods: This comprehensive review explores all of head and neck otolaryngology applications with this sample. We analyzed studies about ear surgery, orbital procedures, parotid gland and facial nerve reanimation, open laryngeal and tracheal surgery, microlaryngoscopy procedures, laryngotracheal stenosis treatment, and diagnostic/operative pediatric endoscopy. For each different procedure, we underline the main applications, similarities, and limitations to human procedures so as to improve the knowledge of this model as a useful tool for surgical training. Results: An ovine model is easily available and relatively inexpensive, it has no limitations associated with religious or animal ethical issues, and it is reliable for head and neck surgery due to similar consistencies tissues and neurovascular structures with respect to humans. However, some other issues should be considered, such as differences about some anatomical features, the risk of zoonotic diseases, and the absence of bleeding during training. Conclusion: This comprehensive review highlights the potentials of an ex vivo ovine model and aims to stimulate the scientific and academic community to further develop it for other applications in surgical education.

Facial nerve regeneration with bioabsorbable collagen conduits filled with collagen filaments: An experimental study

Introduction

A bioabsorbable collagen conduit (Renerve™) filled with collagen filaments is currently approved as an artificial nerve conduit in Japan and is mainly used for connecting and repairing peripheral nerves after traumatic nerve injury. However, there are few reports on its applications for reconstructing and repairing the facial nerve. The present study evaluated the efficacy of the conduit on promoting nerve regeneration in a murine model with a nerve defect at the buccal branch of the facial nerve.

Methods

Under inhalational anesthesia and microscopic guidance, the buccal branch of the left facial nerve in an 8-week-old Lewis rat was exposed, and a 7 mm gap was created in the nerve. The gap was then connected with either the nerve conduits (NC group) or an autologous nerve graft (the autograft group). At 13 weeks after the procedure, we compared the histological and physiological regenerations in the both groups.

Results

We found compound muscle action potential amplitude is significantly larger in the autograft group (2.8 ± 1.4 mV) than in NC group (1.3 ± 0.5 mV) (p < 0.05). The number of myelinated fibers of the autograft group was higher (3634 ± 1645) than that of NC group (1112 ± 490) (p < 0.01). The fiber diameter of the autograft group (4.8 ± 1.9 μm) was larger than that of NC group (3.8 ± 1.4 μm) (p < 0.05). The myelin thickness of the autograft group was thicker than that of NC group (0.6 ± 0.3 μm vs. 0.4 ± 0.1 μm) (p < 0.05). G-ratio of the autograft group (0.74 ± 0.19) was lower than that of NC group (0.79 ± 0.10) (p < 0.05).

Conclusion

This study demonstrated the efficacy of collagen nerve conduit for facial nerve reconstruction following nerve injury. However, the effectiveness of the conduit on the promotion of nerve regeneration was inferior to that of the autograft.

An electrophysiological evaluation method for the ovine facial nerve

Introduction

Large-animal models such as sheep for facial nerve regeneration research have not yet been established because of the lack of methods for assessing the electrophysiological function of regenerated nerves. In this study, we developed a percutaneous measurement method for the evoked compound muscle action potential (CMAP) of the facial nerve in sheep.

Methods

Six 3-year-old castrated male Corriedale sheep were used in this study. Under general anesthesia, an anatomical exploration was performed to identify the course of the buccal branch of the facial nerve and its innervating muscles on one side, followed by the application of surface stimulating electrodes to the contralateral side of the face along the course of the buccal branch of the facial nerve to obtain CMAP measurements of the nasolabial levator muscle.

Results

Percutaneous CMAP measurements of the nasolabial levator muscle could be obtained in all animals by placing stimulating electrodes 1 cm apart on the line coinciding with the course of the buccal branch of the facial nerve revealed by the preceding anatomical exploration. Mean values for electrophysiological parameters were amplitude 4.7 ± 0.7 mV, duration 2.1 ± 0.6 ms, and latency 3.6 ± 0.4 ms.

Conclusion

We have established a percutaneous measurement method for CMAP of the buccal branch of the facial nerve in sheep. This method is expected to be very useful in future studies of facial nerve regeneration for long nerve defects in sheep.

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A percutaneous CMAP measurement method for the ovine facial nerve was established.

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Anatomical experiment demonstrated the method's physiological accuracy.

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The ovine facial nerve enables a more realistic model of facial nerve regeneration.

Omega-7 oil increases telomerase activity and accelerates healing of grafted burn and donor site wounds

This study investigated the efficacy of Omega-7 isolated from the sea buckthorn oil (Polyvit Co., Ltd, Gangar Holding, Ulaanbaatar, Mongolia) in ovine burn wound healing models. In vitro, proliferation (colony-forming rate) and migration (scratch) assays using cultured primary ovine keratinocytes were performed with or without 0.025% and 0.08% Omega-7, respectively. The colony-forming rate of keratinocytes in the Omega-7 group at 72 and 96 h were significantly higher than in the control (P < 0.05). The percentage of closure in scratch assay in the Omega-7 group was significantly higher than in the control at 17 h (P < 0.05). In vivo, efficacy of 4% Omega-7 isolated from buckthorn oil was assessed at 7 and 14 days in grafted ovine burn and donor site wounds. Telomerase activity, keratinocyte growth factor, and wound nitrotyrosine levels were measured at day 14. Grafted sites: Un-epithelialized raw surface area was significantly lower and blood flow was significantly higher in the Omega-7-treated sites than in control sites at 7 and 14 days (P < 0.05). Telomerase activity and levels of keratinocyte growth factors were significantly higher in the Omega-7-treated sites after 14 days compared to those of control (P < 0.05). The wound 3-nitrotyrosine levels were significantly reduced by Omega-7. Donor sites: the complete epithelialization time was significantly shorter and blood flow at day 7 was significantly higher in the Omega-7-treated sites compared to control sites (P < 0.05). In summary, topical application of Omega-7 accelerates healing of both grafted burn and donor site wounds. Omega-7 should be considered as a cost-efficient and effective supplement therapy for burn wound healing.

Accelerated outgrowth in cross-facial nerve grafts wrapped with adipose-derived stem cell sheets

In this study, we devised a novel cross-facial nerve grafting (CFNG) procedure using an autologous nerve graft wrapped in an adipose-derived stem cell (ADSC) sheet that was formed on a temperature-responsive dish and examined its therapeutic effect in a rat model of facial palsy. The rat model of facial paralysis was prepared by ligating and transecting the main trunk of the left facial nerve. The sciatic nerve was used for CFNG, connecting the marginal mandibular branch of the left facial nerve and the marginal mandibular branch of the right facial nerve. CFNG alone, CFNG coated with an ADSC suspension, and CFNG wrapped in an ADSC sheet were transplanted in eight rats each, designated the CFNG, suspension, and sheet group, respectively. Nerve regeneration was compared histologically and physiologically. The time to reinnervation, assessed by a facial palsy scoring system, was significantly shorter in the sheet group than in the other two groups. Evoked compound electromyography showed a significantly higher amplitude in the sheet group (4.2 ± 1.3 mV) than in the suspension (1.7 ± 1.2 mV) or CFNG group (1.6 ± 0.8 mV; p < .01). Toluidine blue staining showed that the number of myelinated fibers was significantly higher in the sheet group (2,450 ± 687) than in the suspension (1,645 ± 659) or CFNG group (1,049 ± 307; p < .05). CFNG in combination with ADSC sheets, prepared using temperature-responsive dishes, promoted axonal outgrowth in autologous nerve grafts and reduced the time to reinnervation.

Polyurethane foam for skin graft fixation in clinical-relevant ovine burn wound model for wound repair and regeneration research

The availability of clinical-relevant large animal models for research in wound healing study is limited. Although a few reports described the wound dressing fixation method using polyurethane foam in patients, no animal studies were conducted to investigate efficacy of the polyurethane foam in grafted burn wounds. In the present study, we report a simple fixation method of grafted burned skin using polyurethane foam dressing (Allevyn Non-Adhesive, smith & nephew, UK) in a clinically relevant ovine grafted burn wound model. The dressing was removed at postoperative day 7 after skin graft. The grafted skin was completely engrafted without any complications. This method was safe and easy to perform and associated with good engraftment without any complications. We believe that the polyurethane foam fixation method may be successfully used in clinical practice as well as in preclinical studies for grafted burn wound repair and regeneration research.