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Nessel et al. Mini-invasive Surg 2023;7:21 https://dx.doi.org/10.20517/2574-1225.2023.21 Page 5 of 8

How influential is the regional load distribution?
Soft tissue simulation has been successful for the computational planning of orthognathic and breast
surgery [38,39] . The first attempts to evaluate the human abdominal wall have been published [40,41] . The
anisotropic distribution of tissue elasticity in scarred battlefield abdomen poses a particular challenge. A
regional load distribution can directly be derived from CT scans of the abdomen at rest and during the
Valsalva maneuver [2,5,18] . The strain values derived from these analyses easily overburden the retention forces
of most meshes . An initial calculation of interfibrillar shear stress of collagenous tissue yields a value
[42]
[29]
corresponding to 224 mmHg . Newly formed collagen fibers are easily overloaded by such strain
values [43,44] . Primary and recurrent incisional hernia develop early but become obvious late [1,45] . Suture
slackening or fascial dehiscence up to 11 mm are obvious after four weeks already. 96% of the cases with
slackened sutures develop an incisional hernia after 40 months. 96% of all incisional hernias, and the
respective recurrences are obvious after ten years. The disregard for the regional load distribution generates
small areas of overload. These are followed by button holes, lattice breakage, and mind-boggling loss of
domain hernia orifices. Considering biomechanical approaches and taking regional load distributions into
[3]
account permits the durable repair of both primary and recurrent incisional hernia repair .

Most important: how can a surgeon apply biomechanics to the clinical case?
An incisional hernia is a frequent consequence of major surgery, causing pain and disability. After repair,
every third hernia recurs, with even worse results after each subsequent redo. In the United States, a cost of
7.5 billion $ is spent per year on incisional hernia repair. In Europe, similar figures have to be expected since
yearly cost amounts in Germany alone to 1.8 billion €. Surgeons, patients, insurance companies, and
policymakers eagerly seek options to lift this burden. Biomechanically stable repair of the abdominal wall
reduces both pain and recurrence after one year, potentially saving most of these costs . For the design of a
[1,2]
GRIP-based durable hernia repair, retention coefficients of the repair materials are mandatory.

In a three-dimensional hernia repair in an abdominal wall, stress and strain effects are observed in all
directions depending on the twist gradients occurring within the given load space. The deformation in
solids, such as hernia meshes, follows the displacement gradient tensor and the deformation gradient tensor
in every volume element within the material . A consequence of these different gradients is local
[14]
instabilities within the reconstruction at the interface of mesh and tissue.

Using cyclic loading in a bench test, such as DIS, described in this study, the effects of local instabilities,
including creeping, tearing, or rupturing, can be observed, providing valuable insights into the
discontinuous mechanisms of failure. In principle, two different options exist after finishing the
reconstruction of a hernia: either the components exhibit low cyclic loading with alternating elastic and
plastic behavior, finally leading to rupture, or tissue, mesh, and fixation cycle into shakedown, where they
take the load at a certain stretch level with purely elastic behavior [25,26] . At this stage, the detailed analysis of
the shakedown process in mesh-augmented human tissues and the effects of plastic strain accumulation
during wound healing and scar formation is still in the early stages of the investigation.

To reach shakedown and permit stable collagen formation, the mesh size must be adapted to the hernia size
and the mesh retention coefficient. The needs of individual patients can be assessed and taken into account.
Fixation is used to reach the required stability. Regional load distribution can be achieved by quilting
[46]
seams . The conceptual design of a durable abdominal wall reconstruction can be applied by every
surgeon . After three years, over 160 patients consecutively operated on in four different hospitals by ten
[2-4]
surgeons have no recurrence. The patients are back in their normal life, pain-free back at work if under 62
years of age. Insurance companies save money on compensation and on redo surgery once biomechanical
considerations are more widespread and applied to abdominal wall reconstruction.