• Derek A DuBay, Winston Choi, Melanie G Urbanchek, Xue Wang, Belinda Adamson, Robert G Dennis, William M Kuzon, and Michael G Franz.
• Department of Surgery, Section of General Surgery, University of Michigan Medical School, Ann Arbor, MI, USA.
• Ann. Surg. 2007 Jan 1; 245 (1): 140-6.

ObjectiveThe purpose of this study is to measure abdominal wall myopathic histologic and mechanical changes during incisional herniation and its effect on incisional hernia repairs.Summary Background DataUnloaded skeletal muscles undergo characteristic atrophic changes, including change in fiber type composition, decreased cross-sectional area, and pathologic fibrosis. We hypothesize that these atrophic changes decrease muscle elastic properties and may contribute to the high laparotomy wound failure rate observed following incisional hernia repair.MethodsA rat model of chronic incisional hernia formation was used. Failing midline laparotomy incisions developed into incisional hernias. Controls were uninjured and sham laparotomy (healed) groups. Internal oblique muscles were harvested for fiber typing, measurement of cross-sectional area, collagen deposition, and mechanical analysis. Mesh hernia repairs were performed on a second group of rats with chronic incisional hernias or acute anterior abdominal wall myofascial defects.ResultsThe hernia group developed lateral abdominal wall shortening and oblique muscle atrophy. This was associated with a change in the distribution of oblique muscle fiber types, decreased cross-sectional area, and pathologic fibrosis consistent with myopathic disuse atrophy. These muscles exhibited significant decreased extensibility and increased stiffness. The healed (sham) laparotomy group expressed an intermediate phenotype between the uninjured and hernia groups. Recurrent hernia formation was most frequent in the chronic hernia model, and hernia repairs mechanically disrupted at a lower force compared with nonherniated abdominal walls.ConclusionsThe internal oblique muscles of the abdominal wall express a pattern of changes consistent with those seen in chronically unloaded skeletal muscles. The internal oblique muscles become fibrotic during herniation, reducing abdominal wall compliance and increasing the transfer of load forces to the midline wound at the time of hernia repair.

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