Latex-Infused Porcine Abdominal Model: A Novel Microsurgery Simulator for Deep Inferior Epigastric Perforator Dissection

Abstract

Background Perforator dissection and flap elevation are routinely performed for microsurgical reconstruction; however, there is a steep learning curve to mastering these technical skills. Though live porcine models have been utilized as a microsurgical training model, there are significant drawbacks that limit their use, including cost, limited ability for repetition, and obstacles associated with animal care. Here we describe the creation of a novel perforator dissection model using latex augmented non-living porcine abdominal walls. We provide anatomic measurements that demonstrate valuable similarities and differences to human anatomy to maximize microsurgical trainee practice.

Methods Six latex-infused porcine abdomens were dissected based on the deep cranial epigastric artery (DCEA). Dissection was centered over the abdominal wall mid-segment between the second and fourth nipple line. Dissection steps included exposure of lateral and medial row perforators, incision of anterior rectus sheath with perforator dissection, and dissection of DCEA pedicle. DCEA pedicle and perforator measurements were compared with deep inferior epigastric artery (DIEA) data in the literature.

Results An average of seven perforators were consistently identified within each flap. Assembly of the model was performed quickly and allowed for two training sessions per specimen. Porcine abdominal walls demonstrate similar DCEA pedicle (2.6 ± 0.21 mm) and perforator (1.0 ± 0.18 mm) size compared with a human's DIEA (2.7 ± 0.27 mm, 1.1 ± 0.85 mm).

Conclusion The latex-infused porcine abdominal model is a novel, realistic simulation for perforator dissection practice for microsurgical trainees. Impact on resident comfort and confidence within a microsurgical training course is forthcoming.

Keywords

resident education - microsurgery - surgical simulation

Utilization of the deep inferior epigastric artery perforator (DIEP) flap for breast reconstruction has increased in popularity over the last decade, mainly due to the reduced morbidity at the abdominal donor site.[1] [2] However, per the 2020 statistics report of the American Society of Plastic Surgeons (ASPS), it was performed in only 9% of breast reconstructions.[3] [4] In addition to other factors contributing to this low incidence, the technical skill needed for performing perforator dissection requires extensive training that may not be readily available at all institutions.[5] [6] Therefore, augmentation of perforator dissection training with simulation is critical.

Options for perforator dissection simulation have primarily been limited to human cadavers or live animal models.[7] Despite the well-described nature of cadaver practice and living animal models, significant roadblocks exist that limit their use. These include resource limitations such as availability, expense, time, and specialized facilities. Additionally, these models require significant preparation, complex disposal processes, and challenges with obtaining and maintaining animal care and use protocols.[8] Non-living animal models are increasingly popular for microsurgical skill acquisition but require perfusion to create adequate realism, such as the blue-blood perfused chicken thigh model.[9] [10] To date, the development of a perfused, non-living animal model for perforator dissection has yet to be successfully described.

This work aims to evaluate the anatomic similarity of the deep cranial epigastric artery (DCEA) perforator flap to the human DIEP flap in a deceased porcine model using latex infusion and confirm the usefulness of this model as a simulator for perforator dissection for microsurgical trainees.

Methods

Six abdomens from adult Wisconsin Miniature Swine were harvested after the terminal surgeries of other institutionally approved studies. The pig's abdomen was cut directly from below the costal margin and extended below the urogenital tract to at least the fifth or sixth nipple line to confirm all anatomic structures were included. Twelve complete dissections were performed after latex perfusion through the DCEA.[11] Anatomic measurements were obtained and compared with existing human DIEP pedicle and perforator measurements from the literature.[6] [12] [13] [14] Measurements included: pedicle diameter at the site of cannulation, the average diameter of dissected perforator (measured at the level of the fascia), and the length of perforator from pedicle to cutaneous insertion.

Additionally, the total number of perforators identified, number of dissected medial and lateral perforators, type of branching pattern (e.g., Type I–III),[15] perforator course (direct cutaneous vs. musculocutaneous), and total dissection time were recorded. Determination of which perforators to dissect was based on clinical judgment. Direct cutaneous perforators were defined as perforators without muscular branches. Musculocutaneous perforators were defined as perforators extending from a muscular branch. A comparison of average perforator number and perforator and pedicle diameter to human measurements was performed using one sample t-test. Statistical analysis was performed with IBM SPSS Statistics version 28 (IBM Corp., Armonk, NY).

Results

Description of Porcine Anatomy

The DCEA flap is the terminal branch of the porcine internal thoracic artery. The flap is centered on the abdominal midsegment between the second and fourth nipples, cranial to the urogenital opening. The pedicle runs in the sub-rectus muscular plane, directly below the nipple line. The medial and lateral perforator rows are adjacent to the nipple line bilaterally ([Fig. 1]).

Fig. 1 Deep cranial epigastric artery perforator flap, centered on the abdominal midsegment between the second and fourth nipples. The pedicle runs in the sub-rectus muscular plane, directly below the nipple line. The medial and lateral perforator rows are adjacent to the nipple line bilaterally.

Apart from the panniculus carnosus, the layers of the porcine abdominal wall are overall similar to human anatomy (e.g., linea semilunaris and linea alba, paired external oblique, internal oblique, transversus abdominis, and rectus abdominis muscles). The panniculus carnosus is a subcutaneous muscle layer that should be identified and maintained with the flap during elevation.

Porcine Perforator Dissection Technique

Dissections were performed under 2.5× loupe magnification by a senior plastic surgeon with specialized training in microsurgery (W.Z.) and post-graduate year-4 plastic surgery resident (E.C.S.). The abdomen was initially placed in the prone position to identify the DCEA vessels running beneath the rectus abdominis bilaterally. The vessels were cannulated using 3 mm angiocatheters and secured with a 4–0 Vicryl suture ([Fig. 2]). Approximately 1 mL of red latex was infused per side using a 3-cc syringe and by applying gentle, constant pressure on the syringe until firm resistance was met. The latex was allowed to set for 20 minutes ([Video S1], available in the online version).

Fig. 2 Cannulation technique. After the abdomen is placed in the prone position, the deep cranial epigastric artery can be identified. Cannulation is performed with 3-mm angiocatheters and secured with suture. Approximately 1 mL of latex is infused.

Video S1 Narrated video capturing porcine abdominal model perforator dissection technique.

The abdomen was then placed skin-side up. The elliptical flap was designed over the second through fourth nipples measuring ∼15 cm × 20 cm per hemiellipse.

Dissection began along the lateral edge of the abdomen, working medially using 15-blade scalpel, just deep to the panniculus carnosus but above the external oblique muscle. Occasionally, a thin layer of prefascial adipose tissue was present and dissected to identify the underlying fascia. Identification of the linea semilunaris indicated a transition from oblique to the anterior rectus sheath, increasing dissector caution for the upcoming lateral row perforators ([Fig. 3A]).

Fig. 3 (A) Exposure of lateral row perforators. (B) Exposure of medial row perforators.

The hemiabdomen was split in the midline, overlying the linea alba with care to avoid injury to the medial row perforators. Dissection proceeded from medial to lateral until medial row perforators were identified. Generally, six to ten perforators were identified between the two rows ([Fig. 3B]).

Perforators to be dissected were selected based on clinical judgment of the largest size, similar to intraoperative selection. The anterior rectus sheath was incised, and subfascial, intramuscular, or submuscular dissection of the perforators was performed back to the level of the pedicle. Attention was paid to the perforator branching pattern (direct cutaneous vs. musculocutaneous), as both can be present on the medial or lateral row ([Fig. 4]). Small branches were identified and coagulated or clipped to simulate maintaining a bloodless operative field. Injury to vessels was identified with latex leakage.

Fig. 4 Demonstration of both direct cutaneous and musculocutaneous perforator branch patterns. DCEA, deep cranial epigastric artery.

Porcine Vessel Measurement

A significantly larger average number of perforators were identified during porcine flap elevation compared with the average number of DIEP perforators (7.5 ± 1.98 vs. 5.2 ±3.5; p = 0.002).[6] An average of 2.8 ± 0.94 (range: 1–5) porcine perforators were selected for dissection. The mean pedicle and perforator diameter measured 2.6 ± 0.21 mm and 1.0 ± 0.18 mm, respectively, with no significant difference found when compared with human DIEP vessel measurements (2.7 ± 0.27 mm [p = 0.139], 1.1 ± 0.85 mm [p = 0.257]; [Table 1]). The predominant perforator course on the medial row was direct cutaneous (70%), while on the lateral row the predominant perforator course was musculocutaneous (69%; [Fig. 5]). All dissections demonstrated a Type I branch pattern. The average length of pedicle dissection was 3.3 ± 0.87 cm; however, lateral pedicle length (3.7 ± 0.96) was slightly greater than medial pedicle length (3.0 ± 0.66 cm) when analyzed by row. The average time for dissection was 91.3 ± 24.2 minutes.

Fig. 5 Frequency of perforator branch pattern by row. (Left) Medial row: 26 (70%) direct cutaneous, 11 (30%) musculocutaneous. (Right) Lateral row: 11 (31%) direct cutaneous, 24 (69%) musculocutaneous.

Table 1 Average number of perforators and average perforator measurements

	Porcine DCEA averages ± SD (range)	Human DIEP averages	p-Value
Total number of perforators	7.5 ± 1.98 (4–10)	5.2 ± 3.5	p = 0.002
Number of perforators selected for dissection	2.8 ± 0.94 (1–5)
Medial	3.1 ± 1.08 (1–5)
Lateral	2.4 ± 0.67 (1–3)
Pedicle diameter	2.6 ± 0.21 (2.28–3.03) mm	2.7 ± 0.27 mm	p = 0.139
Perforator diameter	1.0 ± 0.18 (0.72–1.22) mm	1.1 ± 0.85 mm	p = 0.257
Pedicle length	3.3 ± 0.87 (1.5–6) cm
Medial	3.0 ± 0.66 (1.8–4.2) cm
Lateral	3.7 ± 0.96 (1.5–6) cm
Operative time	91.3 ± 24.2 (49–116) min

Abbreviations: DCEA, deep cranial epigastric artery; DIEP, deep inferior epigastric artery perforator; SD, standard deviation.

p < 0.05.

Discussion

The need for accessible, cost-effective perforator dissection models is becoming increasingly important to overcome the steep learning curve of perforator flap elevation and to maximize technical skills while in training. In the present study, we explore the anatomic similarities and differences between the cadaveric, latex-infused porcine DCEA flap and the human DIEP flap, as well as the model's ability to serve as an accurate simulator for the critical surgical steps in perforator flap elevation for resident trainee education.

No significant difference in average pedicle or perforator diameter was appreciated when comparing the DCEA flap to average human DIEA measurements in the literature.[12] [13] [14] The medial row can be utilized explicitly for practice dissecting shorter, direct cutaneous perforators, while the lateral row can be used for the preparation of longer, musculocutaneous perforators; however, one must keep in mind that the porcine rectus muscle may be thinner than in humans. Regarding notable anatomic differences, all porcine dissections demonstrated a Type I branching pattern with medial and lateral row perforators versus the dominant Type II DIEP branching pattern. We also identified a significantly greater number of porcine perforators during DCEA flap elevation than the average number of DIEP perforators reported in the literature, emphasizing the model's utility for numerous practice opportunities. Additionally, the panniculus carnosus and prefascial adipose must be recognized to complete dissection in the correct plane. Of note, a recent article by Kim et al noted a similar adipose layer surrounding DIEP flap perforators, making this anatomic finding potentially useful for DIEP dissection practice.[16] Lastly, we recognize that the caliber of vessels and rectus muscle thickness may differ in other porcine species, creating variability in the complexity of perforator dissection practice. Overall, the model allows for the practice of surgical marking, flap elevation with perforator identification, proper tissue handling, and careful subfascial and intramuscular dissection.

Previous literature has supported the similarity of porcine anatomy for numerous procedures, including perforator dissection. Loh et al highlighted that pigs were utilized in nearly 70% of all in vivo surgical simulation models.[8] In living porcine models, the DCEA has been proven to be the dominant abdominal cutaneous blood supply, mimicking the human DIEP flap.[11] [17] However, there are numerous obstacles to the routine utility of a live model. Cost analysis of a single live animal dissection, not including the cost of animal purchase and housing, is estimated between $672 and $1,258.[11] Furthermore, in perforator dissection practice, the maximum number of perforators the trainee can dissect is limited in an effort to avoid unnecessary complications or prolonged anesthetic time. These concerns have resulted in recognition of the “3 Rs”: the replacement, reduction, and refinement of animals used in research.[18] Further research has demonstrated comparable intraoperative outcomes of surgical trainees after stimulation with either cadaveric versus living animal models.[19] Compared with live models, cadaveric porcine abdomens are more accessible, ethical, and cost-effective, particularly when obtained at the termination of other studies. Dissection requires only loupe magnification and standard surgical instruments. More importantly, junior residents learning the fundamentals of dissection technique can perform as many perforator dissections as available to refine their skills, maximizing the use of the model.

Originally implemented in human cadavers, latex infusion of our cadaveric porcine DCEA flap model is a novel component for non-living animal simulation that has not been previously described.[20] [21] Our technique utilizes the manual injection of the DCEA vessel after cannulation to allow pressure to fill small caliber, high-resistance vessels. We were able to consistently perfuse to the level of arteriole branches, contradicting other literature arguing that latex filling is suboptimal ([Fig. 4]).[22] [23] Models without some form of perfusion suffer from multiple limitations, with trainees unable to appreciate the intricate vascular anatomy or if vessel injury occurred. When comparing latex-injected human cadavers to non-injected models, latex models demonstrated superior realism given their better vascular integrity, more precise interpretation of intramuscular course, and greater similarity to real-time operating.[24]

While we considered the additional implementation of indocyanine green (ICG) dyed saline to our model, initial attempts at perfusion using a low viscous fluid resulted in extravasation that obscured our dissection planes. A potential reason that this may have occurred was due to an avulsion injury of the vessels during the porcine abdominal harvest. However, in a recent publication by Bravo et al, ICG was successfully combined with latex solution to provide better visualization of vascular supply during anatomic mapping for composite face and whole-eye transplantation in large animal models.[25] We will plan to incorporate ICG into future perforator dissection practice with trainees to enhance feedback during dissection.

This proof-of-concept study describes our model, and its similarities and differences to human anatomy, for perforator dissection practice. Future directions of this project are to obtain resident and faculty assessment of the model for the evaluation of the utility of perforator practice and validation of realism to intraoperative perforator dissection. Furthermore, given the limitation of not having a circulatory system during dissection, we plan for continued evaluation of the model to incorporate perfusion, such as the incorporation of ICG into the latex solution, to improve realism without increasing model cost. Nevertheless, our successful implementation of latex within a non-living animal sets the stage for utilization of this technique in other previously described live porcine flaps that mimic human anatomy, allowing trainees to maximize microsurgical perforator dissection practice opportunities.

Conclusion

The latex-infused porcine DCEA flap provides an accessible, cost-effective simulation of perforator flap dissection. Utilization of this model may help reduce the learning curve of perforator dissection and allow microsurgery trainees to maximize their intraoperative experience. Validation of this model by resident trainees and microsurgery faculty is forthcoming.

Conflict of Interest

None declared.

Authors' Contributions

Conceptualization: E.C.S., W.Z., A.M.D., S.O.P.

Formal analysis: E.C.S.

Investigation: E.C.S., W.Z., J.M.F., P.J.N., S.E.

Methodology: E.C.S., W.Z., A.M.D., S.O.P.

Supervision: A.M.D., S.O.P.

Writing (original draft): E.C.S.

Writing (review and editing): E.C.S., W.Z., P.J.N., S.E., J.M.F., A.M.D., S.O.P.

• References

• 1 Guerra AB, Lyons GD, Dupin CL, Metzinger SE. Advantages of perforator flaps in reconstruction of complex defects of the head and neck. Ear Nose Throat J 2005; 84 (07) 441-447
• 2 Butler PD, Wu LC. Abdominal perforator vs. muscle sparing flaps for breast reconstruction. Gland Surg 2015; 4 (03) 212-221
• 3 Saldanha IJ, Broyles JM, Adam GP. et al. Autologous reconstruction after mastectomy for breast cancer. Plast Reconstr Surg Glob Open 2022; 10 (03) e4181
• 4 Plastic Surgery Statistics | American Society of Plastic Surgeons. Accessed August 22, 2022 at: https://www.plasticsurgery.org/news/plastic-surgery-statistics
• 5 Busic V, Das-Gupta R, Mesic H, Begic A. The deep inferior epigastric perforator flap for breast reconstruction, the learning curve explored. J Plast Reconstr Aesthet Surg 2006; 59 (06) 580-584
• 6 Ireton JE, Lakhiani C, Saint-Cyr M. Vascular anatomy of the deep inferior epigastric artery perforator flap: a systematic review. Plast Reconstr Surg 2014; 134 (05) 810e-821e
• 7 Fresh Cadaver Flap Dissection Course | Duke Department of Surgery. Accessed August 14, 2022 at: https://surgery.duke.edu/education-and-training/continuing-medical-education/courses/plastic-surgery/fresh-cadaver-flap-dissection-course
• 8 Loh CYY, Wang AYL, Tiong VTY. et al. Animal models in plastic and reconstructive surgery simulation-a review. J Surg Res 2018; 221: 232-245
• 9 Zeng W, Gunderson KA, Sanchez RJ. et al. The blue-blood porcine chest wall: a novel microsurgery training simulator for internal mammary vessel dissection and anastomosis. J Reconstr Microsurg 2021; 37 (04) 353-356
• 10 Zeng W, Shulzhenko NO, Feldman CC, Dingle AM, Poore SO. “Blue-blood”- infused chicken thigh training model for microsurgery and supermicrosurgery. Plast Reconstr Surg Glob Open 2018; 6 (04) e1695
• 11 Nistor A, Jiga LP, Miclaus GD, Hoinoiu B, Matusz P, Ionac ME. Experimental swine models for perforator flap dissection in reconstructive microsurgery. PLoS One 2022; 17 (04) e0266873
• 12 Heitmann C, Felmerer G, Durmus C, Matejic B, Ingianni G. Anatomical features of perforator blood vessels in the deep inferior epigastric perforator flap. Br J Plast Surg 2000; 53 (03) 205-208
• 13 Erić M, Ravnik D, Žic R. et al. Deep inferior epigastric perforator flap: an anatomical study of the perforators and local vascular differences. Microsurgery 2012; 32 (01) 43-49
• 14 Colohan S, Maia M, Langevin CJ. et al. The short- and ultrashort-pedicle deep inferior epigastric artery perforator flap in breast reconstruction. Plast Reconstr Surg 2012; 129 (02) 331-340
• 15 Lam DL, Mitsumori LM, Neligan PC, Warren BH, Shuman WP, Dubinsky TJ. Pre-operative CT angiography and three-dimensional image post processing for deep inferior epigastric perforator flap breast reconstructive surgery. Br J Radiol 2012; 85 (1020): e1293-e1297
• 16 Kim YC, Jo T, Hur J, Han HH, Kim EK, Eom JS. Intramuscular deep inferior epigastric vessels are insulated by perimysial fibroadipose tissue network. J Reconstr Microsurg 2022; 38 (08) 664-670
• 17 Roggio T, Pignatti M, Cajozzo M. et al. Porcine model for deep superior epigastric artery perforator flap harvesting: anatomy and technique. Plast Reconstr Surg Glob Open 2018; 6 (02) e1659 DOI: 10.1097/GOX.0000000000001659.
• 18 Curzer HJ, Perry G, Wallace MC, Perry D. The three Rs of animal research: what they mean for the institutional animal care and use committee and why. Sci Eng Ethics 2016; 22 (02) 549-565
• 19 Stefanidis D, Yonce TC, Green JM, Coker AP. Cadavers versus pigs: which are better for procedural training of surgery residents outside the OR?. Surgery 2013; 154 (01) 34-37
• 20 Manna F, Guarneri GF, Re Camilot MDE, Parodi PC. An easy and cheap way of staining the arterial supply of the face: a preclinical study of visualization of facial vascular territories in human cadavers. J Craniomaxillofac Surg 2010; 38 (03) 211-213
• 21 Alvernia JE, Pradilla G, Mertens P, Lanzino G, Tamargo RJ. Latex injection of cadaver heads: technical note. Neurosurgery 2010; 67 (2, Suppl Operative): 362-367
• 22 Doomernik DE, Kruse RR, Reijnen MMPJ, Kozicz TL, Kooloos JGM. A comparative study of vascular injection fluids in fresh-frozen and embalmed human cadaver forearms. J Anat 2016; 229 (04) 582-590
• 23 Bergeron L, Tang M, Morris SF. A review of vascular injection techniques for the study of perforator flaps. Plast Reconstr Surg 2006; 117 (06) 2050-2057
• 24 Chouari TAM, Lindsay K, Bradshaw E. et al. An enhanced fresh cadaveric model for reconstructive microsurgery training. Eur J Plast Surg 2018; 41 (04) 439-446
• 25 Bravo MG, Granoff MD, Johnson AR, Lee BT. Development of a new large-animal model for composite face and whole-eye transplantation: a novel application for anatomical mapping using indocyanine green and liquid latex. Plast Reconstr Surg 2020; 145 (01) 67e-75e

Publikationsverlauf

Eingereicht: 21. September 2022

Angenommen: 21. Februar 2023

Artikel online veröffentlicht:
06. April 2023