Abstract
Objective
To evaluate a fresh, ovine/sheep head and neck tissue model to teach otolaryngology-head and neck surgical techniques.
Study design
Observational animal study.
Setting
A university animal resource facility.
Methods
Tissue was collected from pre-pubescent sheep (n = 10; mean age: 4 months; mean mass: 28 kg) following humane euthanasia at the end of an in vivo protocol. No live animals were used in this study. The head and neck of the sheep were disarticulated and stored at 5 °C for 1–5 days. The tissues were tested in a variety of simulated procedures by a medical student and four fellowship-trained otolaryngology faculty. Practicality and similarity to human surgeries were assessed.
Results
While ovine head and neck structures are proportionally different, the consistencies of skin, subcutaneous tissues and bone are remarkably similar to that seen in human dissection. Particularly useful were the eyelids and orbits, facial nerve and parotid gland, mandible, anterior neck and submandibular triangle. Surgeries performed included blepharoplasty, ptosis repair, orbital floor exploration, facial nerve dissection and repair, mandibular plating, tracheotomy, laryngofissure, tracheal resection and laryngectomy. The model was also useful for flexible and microsuspension laryngoscopy.
Conclusion
Fresh, ovine tissue provides a readily available, anatomically compatible, affordable, model for training in otolaryngology-head and neck surgery. The use of sheep tissues carries a low risk for disease transmission and is ethically defensible. Structural variations in the sheep temporal bone, paranasal sinuses and skull base anatomy limit the usefulness of the model for surgical training in these areas.
1
Introduction
Simulation has gained wide acceptance in medical student and resident education – providing trainees with first-hand exposure to emergency situations and complex procedures while minimizing risk to patients. This is particularly true for surgical training, where simulation allows students to acquire mechanical skills and teachers to document technical competence in standardized fashion . The Consortium of American College of Surgeons–Accredited Education Institutes now supports simulation as a requirement for accreditation of surgical residency programs and the Accreditation Council on Graduate Medical Education lists simulation and skill laboratories as a core competency in surgery graduate medical education .
Researchers have proposed a wide variety of models for head and neck surgical training, ranging from virtual reality to live animals . None is ideal. Fresh human cadavers offer the most obvious surrogate for living patients. Unfortunately, the 2007 United States Safe Tissue Act has markedly limited access to human tissues . Further, human tissues are expensive and pose the greatest risk of disease transmission of any proposed teaching model . Animal rights concerns, and anesthesia and facility expenses limit the usefulness of live animals in surgical education .
Tissues from non-living laboratory or farm-raised animals thus have gained in popularity. Porcine and avian models for soft tissue surgery as well as goat, sheep and dog models for airway reconstruction have been explored with mixed results . Animal hides are structurally quite different from human integument. Endoscopy using excised, mounted larynges is useful for surgical manipulation, but this model does not contain the structure needed to learn suspension laryngoscopy and intubation skills .
We have explored the use of a fresh, saline-perfused sheep head and neck model for surgical simulation. This article describes our initial experience including useful applications and limitations. We believe the ovine model will prove a versatile, flexible and inexpensive teaching tool for simulation of a wide range of otolaryngology-head and neck surgeries.
2
Methods
The ovine tissue collection was conducted at the Temple University Center for Inflammation, Translational and Clinical Lung Research. Storage, dissections and procedures were all conducted at the Temple University Laboratory Animal Resource Facility (ULAR). The tissues utilized were of pre-pubescent sheep ( Ovis aries ), collected at the completion of live animal non-survival lung research being concurrently conducted under Institutional Animal Care and Use Committee (IACUC) approval. The sheep were inspected by a licensed veterinarian to assure good health. Animals were routinely tested for Q fever ( Coxiella burnetii ) according to Centers for Disease Control and Prevention (CDC) protocol. No live animals were used nor were any animals euthanized solely for this study – therefore an IACUC protocol was not required. Tissue was collected from pre-pubescent sheep (n = 10; mean age: 4 months; mean mass: 28 kg). The animals were humanely euthanized as part of the approved initial study (100 mg/kg sodium pentobarbital solution; followed by perfusion with cold physiological saline solution). Post-euthanasia, the head and neck tissue of the sheep was disarticulated 4–6 cm above the sternal notch. The tissue was stored at 5 °C for between 1 and 5 days. After storage, additional dissection was performed to prepare the tissue for pilot training sessions.
Prior to working with fresh ovine tissue, study personnel were enrolled in the university’s occupational health program and were screened for Q-fever antibodies. Personal protective equipment was required, including disposable gowns, head covers, shoe covers, and gloves. Dissection table surfaces were disinfected with MicroChem-Plus™, a detergent/disinfectant recommended for the control of Q fever by the CDC. Changing/showering facilities were available and access to the dissection room was limited via key card security. Sheep tissues were transported in double plastic disposable bags and all carcass material was disposed as biomedical waste through a commercial waste management company. The university has Q fever standard operating procedures in place, which are routinely reviewed and revised by the institution’s occupational health physician.
Cervical and facial dissections were performed on an operating table with the ovine head and neck stabilized with sand bags and/or adhesive tape. Dissection was conducted with the naked eye, loupe magnification or operating microscope using conventional operating room cold-steel instruments and electrosurgical devices. Hospital operative services provided expired suture material and Zimmer Biomet Corporation™ donated mandibular plating equipment.
For the endoscopic procedures, the ovine head and neck preparation was supported in supine position with adhesive tape passed around the operating table. This provided counter-traction against the Karl Storz™ (Tuttlingen, Germany) adolescent Parsons laryngoscope and its Benjamin–Parsons suspension. A Karl Storz™ Tele Pack X system was used for illumination and endoscopic video recording. A Karl Storz™ flexible nasopharyngoscope was used for flexible nasopharyngolaryngoscopy and for transnasal endoscopic intubation. Karl Storz™ Shapshay–Ossoff microlaryngeal instruments were used for endolaryngeal dissection. A 2.7 mm 30° Karl Storz™ rigid rod endoscope provided illumination and magnification.
2
Methods
The ovine tissue collection was conducted at the Temple University Center for Inflammation, Translational and Clinical Lung Research. Storage, dissections and procedures were all conducted at the Temple University Laboratory Animal Resource Facility (ULAR). The tissues utilized were of pre-pubescent sheep ( Ovis aries ), collected at the completion of live animal non-survival lung research being concurrently conducted under Institutional Animal Care and Use Committee (IACUC) approval. The sheep were inspected by a licensed veterinarian to assure good health. Animals were routinely tested for Q fever ( Coxiella burnetii ) according to Centers for Disease Control and Prevention (CDC) protocol. No live animals were used nor were any animals euthanized solely for this study – therefore an IACUC protocol was not required. Tissue was collected from pre-pubescent sheep (n = 10; mean age: 4 months; mean mass: 28 kg). The animals were humanely euthanized as part of the approved initial study (100 mg/kg sodium pentobarbital solution; followed by perfusion with cold physiological saline solution). Post-euthanasia, the head and neck tissue of the sheep was disarticulated 4–6 cm above the sternal notch. The tissue was stored at 5 °C for between 1 and 5 days. After storage, additional dissection was performed to prepare the tissue for pilot training sessions.
Prior to working with fresh ovine tissue, study personnel were enrolled in the university’s occupational health program and were screened for Q-fever antibodies. Personal protective equipment was required, including disposable gowns, head covers, shoe covers, and gloves. Dissection table surfaces were disinfected with MicroChem-Plus™, a detergent/disinfectant recommended for the control of Q fever by the CDC. Changing/showering facilities were available and access to the dissection room was limited via key card security. Sheep tissues were transported in double plastic disposable bags and all carcass material was disposed as biomedical waste through a commercial waste management company. The university has Q fever standard operating procedures in place, which are routinely reviewed and revised by the institution’s occupational health physician.
Cervical and facial dissections were performed on an operating table with the ovine head and neck stabilized with sand bags and/or adhesive tape. Dissection was conducted with the naked eye, loupe magnification or operating microscope using conventional operating room cold-steel instruments and electrosurgical devices. Hospital operative services provided expired suture material and Zimmer Biomet Corporation™ donated mandibular plating equipment.
For the endoscopic procedures, the ovine head and neck preparation was supported in supine position with adhesive tape passed around the operating table. This provided counter-traction against the Karl Storz™ (Tuttlingen, Germany) adolescent Parsons laryngoscope and its Benjamin–Parsons suspension. A Karl Storz™ Tele Pack X system was used for illumination and endoscopic video recording. A Karl Storz™ flexible nasopharyngoscope was used for flexible nasopharyngolaryngoscopy and for transnasal endoscopic intubation. Karl Storz™ Shapshay–Ossoff microlaryngeal instruments were used for endolaryngeal dissection. A 2.7 mm 30° Karl Storz™ rigid rod endoscope provided illumination and magnification.
3
Results
3.1
Facial plastic and reconstructive procedures
The model was used for the following facial plastics procedures: 1) upper and lower lid blepharoplasty, 2) lateral canthotomy and cantholysis, 3) transcutaneous, subciliary and trans-conjunctival approaches to the orbital floor, 4) open microplating of the mandibular body and ramus fractures, 5) superficial and total parotidectomy, 6) facial nerve dissection, division, and micro-anastomosis.
3.2
Assessment
For orbital procedures the soft tissues were very similar in thickness and consistency to human tissues. The eyelid structure was similar to the human and there was a well-defined orbital septum ( Fig. 1 ). The orbital fat pad was not prominent. The ungulate orbital floor was readily recognizable but different in orientation and shape compared to that of binocular primates. Mandibular soft tissues and bone were similar in consistency and thickness to that of humans. Intraoral access was less challenging than expected because of the sheep’s large mouth ( Fig. 2 ). A modified Blair incision was used for parotid and facial nerve exposure. The sheep has three major branches to the facial nerve (auriculo-palpebral, dorsal buccal, ventral buccal). The palpebral division of the auriculo-palpebral branch is subcutaneous and easily found as it crosses the zygoma ( Fig. 3 ). It can be used to trace the nerve retrograde to its trunk. The trunk is similar in diameter and structure to the human facial nerve and served as a good model for microscopic anastomosis ( Fig. 4 ).
