Cadaver as an experimental model to study abdominal wall tension 1

ABSTRACT The use of cadaver as an experimental model to evaluate tension of the abdominal wall after aponeurotic incisions and muscular undermining is described on this article. The tension required to pull the anterior and the posterior rectus sheaths towards the midline was studied in fresh cadavers at two levels: 3 cm above and 2 cm below the umbilicus. Traction measurement was assessed with a dynamometer attached to suture loops on the anterior and posterior recti sheaths, close to the midline, above and below the umbilicus. The quotient of the force used to mobilize the aponeurotic site to the midline and its resulting displacement was called the traction index. These indices were compared in three situations: 1) prior to any aponeurotic undermining; 2) after the incision of the anterior rectus sheath and the undermining of the rectus muscle from its posterior sheath; and 3) after additionally releasing and undermining of the external oblique muscle. The experimental model described showed to be feasible to demonstrate the effects on tension of the abdominal wall after incisions and undermining of its muscles and aponeurosis.


Introduction
The integrity of the abdominal wall must be maintained after reconstructive surgery. 1,2,3,4A technique that decreases the tension at the edges of the defect will decrease the rate of incisional hernias following TRAM flaps, tumor resection and closure of abdominal defects. 5Mesh has been widely used for reconstruction of these defects, decreasing tension is achieved by placing mesh between the edges of the defect. 6,7Since low tension at closure reduces aponeurotic dehiscence, there has been a movement toward inserting synthetic mesh in the past few years.However, the use of synthetic material may cause complications such as local chronic infection, mesh extrusion, bowel perforation and formation of fistulae.
Good abdominal wall support and maintenance of contractility are important goals of abdominal wall reconstruction. 8,9Contractility however, is not obtained with the use of mesh.Also, the use of adjoining tissues during reconstruction will avoid the complications previously described.Do allow medial mobilization of the abdominal wall with lower resistance at closure?

Proposition
The purpose of this study is to report and bring to light the use of cadaver as an experimental model to evaluate tension of the abdominal wall after aponeurotic incisions and muscular undermining.

Anatomic Study
Fresh adult cadavers were dissected at room temperature (22 o C.) and studied from December 1994 to April 1996.None had had abdominal wall incisions or hernias.Ages ranged from 34 to 82 years, the median being 53.5 years.Cadavers from both genders were studied.
The cadaver was placed in supine position.An incision from the xyphoid process to the pubis exposed the linea alba.The fat was dissected from the aponeurosis by sharp dissection, as in the abdominoplasty procedure.The two levels to be studied were marked at three centimeters above (superior level) and two centimeters below (inferior level) the umbilicus (Figure 1 and 2).The midline served as a reference for all measurements performed.A suture was used to mark the midline.Traction was measured by placing the dynamometer perpendicular to the suture and parallel to the aponeurosis (Figure 5).Each measurement was repeated by a second observer.In the case of discrepancy, a third observer would make a measurement, and the two in closest agreement were selected for.The sequence of anatomic dissection will be described as follows:

Traction measurement of initial stage
After aponeurotic exposure, traction was measured at sites rsa, lsa, ria and lia.Two longitudinal incisions were made on the anterior rectus sheath, next to the linea alba, from 2 cm below the xyphoid process to the arcuate line.These incisions were made to approach the posterior rectus sheath.At this point no dissection was performed.Traction was measured again at the same sites of the anterior rectus sheath.Therefore, two values of traction were obtained at each site of the anterior rectus sheath at the initial stage.
Four sutures with loops, rsp, lsp, rip and lip, were placed in the posterior rectus sheath.They were placed at the same level as those at the anterior rectus sheath.Traction to the midline of these sites was also measured (Figure 6).

Traction measurement of stage 1
The rectus muscles were completely dissected from their posterior sheaths.However, they were kept attached to the anterior aponeurosis.At this point, traction of the eight sites was measured (Figure 7).

Traction measurement of stage 2
Incisions were made at the semilunaris line, dividing the aponeurosis of the external oblique from the costal margin to the reflected inguinal ligament.These muscles were undermined laterally to the anterior axillary line where the vascular pedicle penetrates the muscle; superiorly to the costal margin; and inferiorly to the inguinal ligament (Figure 8).Traction was again measured at the eight sites.

FIGURE 1 -FIGURE 2 -
FIGURE 1 -Area of rectus diastasis is marked as well as the superior and inferior levels -3 cm above and 2 cm below the umbilicus.

FIGURE 3 -
FIGURE 3 -Scheme demonstrating the location of the aponeurotic sites: A -Supra-umbilical level sites rsa, lsa, rsp e lsp; B -Infra-umbilical level sites ria, lia, rip e lip.

FIGURE 4 -
FIGURE 4 -Dynamometer used to measure traction of the abdominal wall.

FIGURE 5 -
FIGURE 5 -Traction measurement on the right superior posterior site (rsp).Note the dynamometer' s hook, positioned perpendicularly to the midline.The traction was measured tangentially to the aponeurosis

FIGURE 6 -
FIGURE 6 -Suture loops on the supra and infra umbilical sites, on the anterior and posterior rectus sheath.

FIGURE 8 -
FIGURE 8 -Stage 2 -Incision of the external oblique aponeurosis along the semilunaris line and undermining of the muscle laterally to the anterior axillary line.