Keywords
surgical simulation - surgery education - pig model
Breast reconstruction is one of the most common reconstructive procedures performed
by plastic surgeons worldwide,[1] with reconstruction using autologous free tissue transfer as the procedure of choice
for an increasing number of breast cancer patients.[2] The internal mammary vessels are the primary recipient vessels for these operations.[3]
[4]
Appropriate preparation of the internal mammary artery (IMA) and internal mammary
vein (IMV) is a critical step of this procedure. Vessel damage can result in failure
of the intended reconstruction and operating on the chest wall poses a risk of other
complications including pneumothorax.[5] Given the technical complexity of chest vessel exposure and the concomitant risk
of untoward outcomes, the stress of learning the technique in the operating room (OR)
is amplified for both the teacher and the learner, even in a controlled environment
under supervision.
Existing high-fidelity models utilized in surgical education, such as the blue-blood
perfused chicken thigh model, provide realistic simulation for microvascular anastomosis
training,[6] but there are no simulators for practicing appropriate approach to isolating the
internal mammary vessels including dissection, rib excision, and vessel preparation.
All of these are key aspects of the procedure that residents and fellows must learn
to perform. Although live pig models provide more authentic simulation for these skills,
they are inconvenient, prohibitively expensive to maintain, and demand a veterinary
anesthesiologist for training sessions. Given this, our aim was to create a simple,
inexpensive, and realistic model for resident training of IMA dissection and anastomosis.
Methods
Anatomic Comparison
Chest walls from adult Wisconsin Miniature Swine were harvested at the completion
of other studies at our institution. Five chest walls were dissected for anatomic
comparison with existing human data. Rib width, intercostal space (ICS) width, IMA
and IMV diameters, distance from lateral sternal border to IMV, and distance from
costochondral junction to IMA were measured. Observational comparisons between the
pig and humans were also made. A dissected porcine thorax is shown in [Fig. 1].
Fig. 1 Porcine chest wall dissected to show blue-blood perfused internal mammary vessels
coursing deep to the ribs.
Materials
The materials used for the simulator are inexpensive and easy to obtain. Items needed
include cadaveric porcine chest wall (obtained at no cost), two plastic mannequin
torso shells (SSWBasics Male Molded Shirt Form, Amazon), 12 × 12 × 1 in layer of multipurpose
foam (Future Foam, Home Depot), and two rubber bands. This model is enhanced with
the addition of a blue-blood perfusion system, previously utilized in a chicken thigh
model for microsurgical training.[6]
[7] Standard surgical instruments can be used.
Model Assembly
Once harvested, chest walls are frozen for storage and thawed for use without disturbance
to anatomy or reduction in model quality. Release of the sternoclavicular joint allows
the chest wall to lay flat in a position more analogous to humans. The blue-blood
system is set up to perfuse the IMA and IMV during training sessions as previously
described.[7] The model is assembled in four layers. A plastic mannequin shell comprises the first
layer and provides rigidity to the model. The perfused chest wall is placed as the
second layer. A layer of upholstery foam, mimicking human subcutaneous fat, is situated
on top of the chest wall and adds realistic depth. The second mannequin shell is placed
as the final layer. An elastic band is placed around all layers at the neck and waist
for stabilization. Two holes are made near the neck of the bottom mannequin shell
and the sternum of the top mannequin shell for inflow and outflow tubing of the perfusion
system to pass. The fully assembled model is shown in [Fig. 2].
Fig. 2 Fully assembled internal mammary artery training model.
Results
This model can be assembled quickly with a low, one-time cost of approximately $55.00.
Anatomically, porcine chest walls are similar to human chest walls, with suitable
likeness in vessel diameter and location. A detailed comparison of model anatomic
measurements with existing human data are shown in [Table 1].[8]
[9] We found that pig ribs are slightly flatter, wider, and have a steeper costochondral
angle than human ribs. Additionally, the porcine sternum widens caudally such that
it overlies the IMA and IMV at the level of the fifth and sixth ribs. Based on these
data and experience, the most realistic simulation can be performed at the second,
third, and fourth ICSs. Once assembled, the depth from mid-sternum to internal mammary
vessels is approximately 5 cm. An image from a training session after identification
of these vessels is shown in [Fig. 3]. Training on this model is analogous to performing these steps in the OR ([Video 1]).
Video 1
Narrated video captured through a surgical microscope showing a resident training
session on the novel blue-blood pig thorax simulator.
Fig. 3 Image taken during resident training session after dissection, rib excision, and
identification of internal mammary vessels.
Table 1
Comparison of pig and human chest wall measurements
|
Pig bilateral averages (mm)
|
Human bilateral averages (mm)[8]
[9]
|
|
Rib width
|
ICS width
|
IMA diameter
|
IMV diameter
|
Sternal border to IMV distance
|
Costochondral Junction to IMA distance
|
Rib width
|
ICS width
|
IMA diameter
|
IMV diameter
|
Sternal border to IMV distance
|
Costochondral junction to IMA distance
|
|
Second
|
15.3
|
12.8
|
3.9
|
5.8
|
5.3
|
12.1
|
11
|
17.5
|
3.0
|
3.3
|
6.1
|
12.8
|
|
Third
|
16.6
|
12.3
|
3.8
|
5.4
|
5.3
|
16.9
|
12.6
|
14.1
|
2.8
|
3.0
|
9.0
|
24.8
|
|
Fourth
|
16.3
|
8.8
|
3.4
|
5.1
|
1.9
|
24.1
|
12.8
|
9.8
|
2.5
|
2.6
|
10.5
|
33.3
|
Abbreviations: ICS, intercostal space; IMA, internal mammary artery; IMV, internal
mammary vein.
Discussion
Simulation is an integral part of surgical and microsurgical education as it provides
a safe and controlled environment for the acquisition of skills prior to entering
the OR.[10] Formal incorporation of simulation in microsurgery training curriculum, however,
is lacking, and trainees feel dry laboratory skill training with simulators is underutilized.[11] Innovative training models have been created in many areas of microsurgery from
microsurgical and supermicrosurgical anastomoses to harvesting of ALT flaps, but a
model of internal mammary vessel dissection currently does not exist.[7]
[12]
The domestic pig is an animal model used frequently in medical research for its anatomic
and metabolic similarity to humans.[13]
[14]
[15]
[16]
[17] As a preclinical model, the importance of the domestic pig cannot be overstated.
They are frequently used at academic institutions and thus are readily available.
We have found it is easy to obtain cadaveric porcine chest walls at the termination
of other studies on our campus, which is cost-effective and ethically supports the
three Rs (replacement, reduction, and refinement) of animal research.[18]
The utility of live and cadaveric pig specimens as surgical training tools has shown
to be effective in many instances, from kidney transplants to lymphaticovenular anastomoses.[19]
[20]
[21]
[22] We have shown this similarity and potential as a surgical training model translates
to the dissection of internal mammary vessels. Though there are some anatomic differences
between the porcine thorax and the human thorax, as a whole, this simulator has good
face validity and is well suited for training of plastic surgery residents for the
preparation and anastomosis of the internal mammary vessels. Formal incorporation
of this model into our program's microsurgery training curriculum has been well received.
Resident and faculty perspectives on the realism and utility of the model will be
published in a forthcoming study.
Further, based on the anatomical and geometric configuration of the rib spaces, with
homologous anatomy and similar ICS width, the model is also suitable for practicing
rib-sparing internal mammary isolation.[23]
[24] Though the focus of this paper was on the more traditional nonrib-sparing technique
to demonstrate feasibility of the swine thorax, the simulator is well suited for future
studies on various methodologies of internal mammary isolation (rib-sparing vs. nonrib-sparing)
and microsurgical anastomosis (loupe vs. microscope).
Overall, this model can be assembled quickly, at low cost, and allows for multiple
training sessions per specimen. Residents are able to practice steps beyond microsurgical
anastomosis, such as dissection to rib, incision and elevation of perichondrium, excision
of rib, identification of vessels, end-to-end anastomosis of IMA, and use of venous
coupler on IMV, all while working at a realistic depth. Augmentation of this model
with a perfusion system creates a highly realistic simulation experience allowing
for real-time feedback of anastomotic quality.
Conclusion
The blue-blood porcine chest wall model provides simple, inexpensive, and realistic
simulation of IMA preparation and anastomosis. Training with this novel model can
bridge the gap between existing basic microsurgical models and the OR for performing
these key steps of autologous breast reconstruction.
