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Lesch et al. Mini-invasive Surg 2023;7:25 https://dx.doi.org/10.20517/2574-1225.2023.31 Page 5 of 13

current installation of the bench test design. The bench test can assess a variety of reconstruction techniques
and materials. It allows examining commercially available materials by factorizing their properties.

In general, porcine abdominal walls or bovine flanks are suitable model tissues. The porcine tissues consist
of all abdominal wall layers that have similar characteristics to the human abdominal wall. The bovine
tissues are thinner and include only the oblique abdominal muscles. The two tissues differ in their elastic
[20]
properties and have distinct median elasticities . That allows mapping the elastic bandwidth of the
abdomens of patients. Human abdomens show up to 18-fold variability in tissue extensibility. The variation
[10]
is lower in porcine and bovine tissues with a ratio of 1:4 but covers 95% of the variation in 123 patients .
Thereby, the extensibility behavior of human, porcine, and bovine tissues is comparable with a median of
20%. A variety of defects differing in form (incision, circular, rhomboid, or elliptic), size, and direction
(median, lateral, transverse, horizontal) can be applied. The defects can be reconstructed with sutures and
meshes in all techniques. This is our standard for the evaluation of coefficients for meshes, fixation
elements, and techniques. An EPDM plate is used to limit the impact area. The area can be adjusted
®
between 20 cm² to 496 cm². Peak pressure values can be varied between 50 and 350 mmHg. Basal pressures
can be adjusted from zero up to 80 mmHg. It is usually kept between 4 and 10 mmHg. Pressure plateau
values are held at a minimum of 100 msec but can be increased if needed.

For the purpose of the experiments reported here [Table 2], we used porcine bellies with a 5 cm large round
central defect [Figure 1, right]. These defects (ES 1-13) were bridged in a sublay position with a 15 × 15 cm
®
large Cicat Dynamesh. In series 14-16, the defects were located in an additional 15 cm incision to simulate
an incisional hernia. We sutured them in a standardized small-stitch-small-bite technique. We used a 2-0
PDS suture with a suture-to-wound-length over 4:1. Then we mounted the tissues on the test bench [
®
Figure 1, left]. A third of our patients cough more than 400 times in the first 24 h postoperatively .
[1]
Accordingly, we loaded the reconstructed tissues 425 times with cyclic pressure impacts. One series was
conducted with 1,000 impacts, simulating a worst-case postoperative scenario. We varied the maximum
pressure peaks to 120, 150, 180, 210, and 240 mmHg. The length of the maximum pressure plateau was 0.1,
0.2, or 0.4 seconds. We conducted two series with a higher basal pressure (set off) of 40 or 80 mmHg. Two
different cover plates for the test bench were used. One had a square 16 cm (256 cm²) large opening. The
second one had a circular 25 cm (490 cm²) large opening. The experiment was finished when the mesh
dislocated or the suture reopened, revealing the plastic sack beneath. Table 2 contains a detailed overview of
the conducted experiments and the individual setup.

Application of biomechanical parameters to patient care
Figure 2 shows the analysis of the abdominal wall CT scans of two patients. The shift and distortions were
assessed in mm while resting or during the Valsalvas maneuver (CTAV).

The bench test mimics these lifelike conditions. It assesses the behavior of the abdominal wall and an
existing defect during stress. The knowledge from our experiments and the preoperative CT scans [Figure 2
] enables the application of biomechanical parameters to patient care [Figure 3], as already published [2,7,8] .

RESULTS
Influence of the test bench parameters on the abdominal wall and hernia repair
Our test bench provides a suitable assessment method by examining compounds under lifelike
circumstances . Experimental series (ES) 1-13 studied the tissue behavior under varying maximum
[4]
pressure and varying pressure plateau lengths.