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Porcine Model for training in Oncoplastic Breast Surgery

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B. Acea Nebril, A. García Novoa, A. Bouzón Alejandro, A. Centeno Cortes.
Journal of Plastic, Reconstructive & Aesthetic Surgery 2019.
https://doi.org/10.1016/j.bjps.2018.12.049

Breast surgeons need specific training in oncoplastic and reconstructive procedures for planning a surgery specific to the breast and the tumor (1,2,3). This training requires a training model whose anatomical and technical bases are similar to the human in order to step by step recreate the most complex surgical procedures. The porcine model provides an option for this training need thanks to its anatomical similarity to humans, manageability of young specimens and relative cost (4). As a result, its use has facilitated training in different areas of digestive and cardiovascular surgery. However, there are few publications that evaluate this model for breast surgery training (5) and none of them has evaluated its viability in a project for training in oncoplastic and reconstructive techniques in breast surgery.

The objective of this study is to describe a porcine model for performing latissimus dorsi muscle flaps  (LDMF) and transverse rectus abdominis muscle (TRAM) flaps during a continuous training program in breast surgery, as well as their evaluation by some of the students to learn about their strengths and weaknesses.

Material and Method

Course Description This oncoplastic and reconstructive breast surgery course was planned through a continuing training program of the Ministry of Health in Spain and was accredited through an assessment agency (6) that reports to the public health administration. This agency accredited 69 classroom hours with 14.6 credits from the Spanish Ministry of Health, equivalent to 104.2 CME credits.

Course of Oncoplastic & Reconstructive Breast Surgery. 14th Edition. 2018

The course program was organized around four modules: a first module on general subjects related to planning of oncological surgery (13 hours), a module on oncoplastic techniques (23 hours), a third module on reconstructive techniques (28 hours), and a fourth module for a practical workshop on muscle flaps (5 hours). The theoretical sessions were taught using multimedia projection (presentations, videos), and the practical part was organized through a practical workshop in the porcine model. At the end of each session, the students completed a questionnaire to evaluate the subjects taught and the teaching staff. Finally, a final exam was carried out to evaluate the training received.

The practical workshop on the porcine model consisted of the execution of an LDMF and TRAM flaps by each student, and was carried out at two training centers in A Coruña (Spain) and Mexico City (Mexico). Large white female pigs with a weight between 30-35 kg were used. The surgery was performed under general anesthesia with intubation and mechanical ventilation. The animals were handled within the ethical and legal framework established by Spanish (7) and Mexican (8) legislation. One animal (pig) was available for every two students and each student performed both procedures as surgeon and as assistant. The course teachers supervised the surgical interventions carried out by each student and evaluated the final result, especially the vascular viability of the flap at the end of the surgical intervention. Finally, the students responded to a questionnaire in which each technical procedure was evaluated individually to learn about their strengths and weaknesses.

Finally, a list was prepared to register eligible students (those who passed the theoretical and practical tests of the course) in the continuous training assessment agency, and diplomas accrediting this training course were granted.

Description of the Animal Model

Latissimus dorsi muscle flaps. The layout of the latissimus dorsi muscle in pigs is similar to humans in terms of its location and anatomical features. The muscle body is located at an intermediate point between the olecranon and the scapula, and thus the cutaneous island was designed in said location (Figure). Once the skin was incised, the panniculus adiposus was dissected subcutaneously to release the muscular surface and define the limits of the latissimus dorsi muscle with respect to the trapezius muscle. As in the human model, dissection in the medial direction allowed the identification of the trapezius muscle and finally the separation of the flap from the thoracic wall. During this maneuver, several intercostal perforators were visualized, dissected and ligated. The flap was then released cephalad to the pedicle allowing the identification of the serratus major muscle. Its identification and dissection are simple, which facilitated the progression towards the tendinous portion of the muscle and the vascular pedicle. In this tendinous portion, the thoracodorsal vessels were dissected and the tendon was sectioned for better release of the LDMF.

Dissection of the LDMF in the porcine model

TRAM flap. The anatomical layout of the anterior rectus abdominis muscle in the pig is similar to that of the human with the exception of an anatomical variant in this animal, i.e. the presence of the greater oblique muscle as the muscular front of the abdomen. Unlike the human, in whom the anterior rectus muscle constitutes the only anatomical element of the abdominal wall in its medial third, the porcine model has a greater oblique muscle that completely covers the abdominal cavity in the most superficial plane, from the paravertebral muscles to the midline, with the exception of the hypogastrium, where the abdominal wall is constituted exclusively by the anterior rectus muscle in its middle third.

Planning a TRAM flap in the porcine model should take into account three technical details. First, it is necessary to select a female animal for the procedure, since the urogenital apparatus of the male makes difficult to dissect the flap in the abdominal midline. Second, the presence of the greater oblique muscle above the anterior rectus makes it necessary to create the cutaneous island of the flap in the hypogastric region to recreate the same conditions as in humans. Third, mobilization of the muscle body of the anterior rectus should be performed underneath the greater oblique muscle, and not subcutaneously as in humans.

The TRAM flap in the pig begins by designing two cutaneous islands in the hypogastric region for better educational use of the animal. Once the skin was incised, the island remained attached to the aponeurosis and dissection was started cephalad, between the aponeurosis surface of the anterior rectus and the body of the anterior rectus to facilitate its mobilization with the cutaneous island. Once the muscle body was released, it was sectioned under the cutaneous island and the ligature of the epigastric vessels. After this maneuver, we were able to mobilize the TRAM flap cephalad, as is done in humans.

Dissection of the TRAM flap in the porcine model

Results

During the years 2015-2018, a total of 6 training courses were organized in oncoplastic and reconstructive breast surgery with the use of the porcine model as a complement to the theoretical part, four of which were held in Spain and two in Mexico. A total of 253 students participated in these courses (140 men and 113 women) with an average age of 42.3 years. The majority of the students were Spanish (122) and Mexican (68), although other students from European countries (Portugal 20, Italy 2, France 1, Greece 1) and Latin America (37) also attended. Oncological surgery was the surgical specialty of most of the participants (179), followed by gynecology (71) and plastic surgery (3).

Two students declined participating in the practical workshop for ethical reasons, while the remaining 251 students fully completed the execution of the two muscle flaps proposed in the program. The average time for performing the latissimus dorsi muscle flap was slightly longer (38.3 minutes) than the TRAM flap (32.6 minutes).

The main reasons for carrying out this course were the need for specific training in oncoplastic techniques, advancing knowledge in surgical techniques and providing better opportunities for patients. The students highlighted the clarity of the presentations, the practical orientation of the program and the accessibility of the teaching staff as the main positive elements of the course. On the contrary, the main criticism for the course was the excessively long hours each day and the density of the program.

The assessment of the porcine model for flaps was different for each technical procedure. Thus, in assessing the model for the LDMF, the students highlighted its similarities to the human regarding different technical aspects, among which they emphasized the mobilization of the muscle from the thorax, the section of the lumbar perforators, the identification of the thoracodorsal pedicle and the  section of the muscular tendon. On the contrary, they highlighted greater difficulty in the porcine model in regard to the identification of the anatomical boundaries of the muscle, especially its medial edge, as well as the paleness of the muscle fibers that limited their dissection. The students highlighted the similarity of the TRAM flap to the human model in terms of the dissection and release of the rectus abdominis muscle as well as its mobilization to the recipient area. On the contrary, they highlighted greater precariousness of the porcine model in regard to adherence of the cutaneous island to the aponeurosis of the rectus abdominis, and greater fragility of the peritoneum in the posterior sheath of the muscle. The majority of the students (246) considered the TRAM technique more accessible in this model with respect to the dorsal muscle flap.

The total cost of the six practical workshops amounted to 61,797 euros, which is an average of 244 euros per student. However, the cost of the workshop in the Spanish edition was significantly more expensive (297 euros/student) with respect to the cost of the Mexican edition (115 euros/student).

Discussion

Demand for education and training in oncoplastic and reconstructive surgery has been increasing among breast surgeons. Surveys carried out at a consensus conference on oncoplastic surgery (1) showed that surgeons believe that oncoplastic surgery should be performed by breast surgeons, which requires more training in these procedures. The majority of the participants believed that in the future oncoplastic and reconstructive procedures will be part of the training curriculum for breast surgery. Our results are also along this line, since the main reason our students took the course was the need for technical, general or specific improvement in oncoplastic techniques. Likewise, we must emphasize that 18% of our students state the benefit of their patients as their main motivation for training, which undoubtedly constitutes an ethical motivation that has not been previously reflected in other studies. As for the elements that were most valued during the training, our students highlighted the practical orientation of the course (program and practical workshop), the clarity of the presentations and the teaching staff. These results suggest that training in oncoplastic and reconstructive breast surgery should be based on practical description of the surgical procedures by surgeons who are experts in this subject, who also contribute their personal experience. The use and presentation of edited videos (10-15 minutes) that reflect the fundamental steps of each procedure is another outstanding element in the surgeon’s training, especially with regard to their availability (multimedia or online files), so that the surgeon can watch them at the hospital at the time of performing the procedure. Likewise, the introduction of oncoplastic training devices, such as the mastotrainer (9), can improve the options for specific training in pattern design and oncoplastic resection.

The similarity of the pig and human anatomies has advanced its use as a surgical training model in laparoscopy and organ transplantation. Its use in the context of breast surgery has focused on training for free flaps (4), execution of random flaps (10) and training for mobilization of the nipple-areolar complex (NAC)[Office1]  (11). This animal has also been used for researching lymphatic drainage in lymphedema (12), studying venous drainage alterations in the genesis of flap necrosis (13), and preparing three-dimensional models for the creation of flaps dependent on perforators (14).

The use of pigs as a training model for the LDMF is based on the studies of Millian (4), who in 1985 described the anatomy of this animal and compared it with the human anatomy. As far as we know, this publication is the first study that evaluates the use of this model for LDMF training by students. Our study confirms that the anatomical similarity of the porcine model to the human model is identified by the students as the main advantage of the model that justifies its inclusion in training programs. The main limitation of the model for this procedure is the initial difficulty in identifying the limits of the latissimus dorsi due to the paleness of the muscle with respect to human muscle, and the absence of an anatomical boundary between this muscle and the pectorals. In spite of this fact, all students have completed the execution of this flap in an optimal amount of time, which shows its validity for training.

The TRAM flap has been used as a research model on local circulation in this flap (15) and in the DIEP flap study (5). As in the porcine model for the LDMF, there are no studies that evaluate its use in the training of breast surgeons. Our study confirms that it is viable as a training model thanks to its morphological similarity to human anatomy. The great majority of the students identified this flap as a less complex procedure compared to the LDMF, certainly due to its better anatomical definition, as reflected in the shorter duration of surgical time.

In addition to the flaps analyzed, the porcine model offers other possibilities for training in oncoplastic and reconstructive breast surgery that have not been evaluated in this study. Procedures related to the NAC stand out since this model allows mobilization of the NAC by means of circular patterns, free NAC grafts, NAC reconstruction by local flaps, and NAC dissection of the with a vascular pedicle. Also, this model allows training with implants associated with the flaps described above by placing expanders or silicone prostheses.

Round-Block and inferior pedicle in the Porcine Model

The costs of this training model have varied depending on the country in which it was carried out, and thus our study shows a price reduction of more than 50% per student in Mexico with respect to Spain. These cost differences are related to the local price of the animals, the cost of labor and the maintenance of the training centers as well as the tax differences between the two countries. Despite these cost differences, we believe that the model has a good cost/benefit ratio since it allows the training of two surgeons not only for the execution of four pedicled flaps, but also for training in different procedures related to the NAC and the placement of implants.

This study has several limitations. First, the technical capacity of each attending student prior to the course has not been evaluated, which makes it impossible to know the degree of initial competence of the students. Second, there is no post-course evaluation that can inform us about the incorporation of these two procedures into surgical practice by the attendees.

This experience allows us to conclude that the porcine model is suitable for surgical training in LDMF and TRAM flaps thanks to its anatomical similarity to humans. The model allows most of the technical steps to be recreated in both flaps, which allows for training prior to its execution in humans. Finally, the use of an animal by two surgeons and the joint execution of flaps and local procedures, especially those related to the NAC, provides a model with a good cost/benefit ratio for surgical training.

References

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4. Millican P, Poole D. A pig model for investigation of muscle and myucutaneous flaps. Br J Surg 1985; 38: 364-368

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6. SAGa Portal of Providers. https://extranet.sergas.es/sagap/sagap/Inicio.aspx?Idioma=es (Spanish)

7. Royal Decree 53/2013, of February 1, which establishes the basic rules applicable for the protection of animals used in experimentation and other scientific purposes, including teaching. Official State Bulletin, Friday, February 8, 2013. https://www.boe.es/boe/dias/2013/02/08/pdfs/BOE-A-2013-1337.pdf.

8. Official Mexican Standards NOM-062-ZOO-1999, Technical specifications for the breeding, care and use of laboratory animals. http://www.ibt.unam.mx/computo/pdfs/bioterio.NOM-062.pdf.

9. Zucca-Matthes G, Lebovic G, Lyra M. Mastotrainer new version: Realistic simulator for training in breast surgery. Breast 2017; 31: 82-84.

10. DeLuca L, Beckenstein M, Guyuron B. Yucatan pig: An optimal hairless model for a true random cutaneous flap. Aesthetic Plast Surg 1997; 21 (3): 205-6.

11. Christofides E, Potgieter A, Chait L. Nipple migration in a pig using the technique of serial excision. Br J Plast Surg 2005; 58 (7): 908-13.

12. Ito R, Suami H. Lymphatic Territories (Lymphosomes) in Swine: An Animal Model for Future Lymphatic Research. Plast Reconstr Surg 2015; 136 (2): 297-304.

13. Minqiang X, Jie L, Lanhua M, Dali M. A new experimental venous super-drained transmidline abdominal skin flap model in pig. J Plast Reconstr Aesthet Surg 2010; 63 (10): e764-5.

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15. Dorion D, Boyd J, Pang C. Augmentation of transmidline skin perfusion and viability in transverse rectus abdominis myocutaneous (TRAM) flaps in the pig. Plast Reconstr Surg. 1991; 88 (4): 642-9.

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