Evaluation of Abdominal Wall Remodeling Following Ventral Hernia Formation in a Rodent Model

David M Krpata, MD, Karem C Harth, MD, Jeffrey A Blatnik, MD, Michael J Rosen, MD. Case Comprehensive Hernia Center, University Hospitals Case Medical Center

Introduction: Mediating abdominal wall function, the linea alba is a major tendinous insertion for abdominal wall musculature. When tendons are severed in limb muscles, changes classic for disuse atrophy appear. Similarly, when a ventral hernia occurs, particularly following a midline laparotomy, the linea alba attachment is lost and abdominal wall muscles may laterally retract and potentially undergo disuse atrophic changes. The objective of this study was to evaluate in a rat model the abdominal wall remodeling that occurs after the unloading of the core abdominal wall musculature with ventral hernia formation.
 

Methods: The linea alba of Sprague-Dawley rats were incised and rats were survived for 30 days to represent a model of chronic ventral hernia. At 30 days, abdominal wall samples were evaluated for changes in muscle fiber type and size with histologic analysis, changes in muscle biomechanics and changes in gene expression with Affymetrix GeneChips to potentially associate downstream effects of ventral hernias with abdominal wall remodeling.
 

Results: In total, 10 Sprague-Dalwey rats underwent hernia formation (Hernia) and were compared 10 Sprague Dawley normal abdominal walls (Control). Mean size of the hernia defects at 30 days was 4.52 cm2 (range 2.5-6 cm2). On histologic analysis, there was no significant difference in number of Type I muscle fibers or Type I fiber total percent area in either the external abdominal oblique muscles (Control: 413 fibers ± 216; 4.62% ± 1.29: Hernia: 481 ± 297 fibers; 5.11% ± 1.56) (p=0.30; p=0.18) or internal abdominal oblique muscles (Control: 311 fibers ± 241, 5.96% ± 1.25; Hernia: 442 fibers ± 231, 6.03 ± 1.90) (p=0.06, p=0.88). The biomechanical properties of unloaded and normal abdominal walls were similar in tensile strength (Control: 1.90 N/mm2 ± 0.72; Hernia: 1.82 N/mm2 ±0.38) (p=0.71), toughness (Control: 126.37 J ± 48.18; Hernia: 105.89 J ± 25.37) (p=0.16), and stiffness (Controls: 1.05 N/mm ± 0.5; Hernia: 1.00 N/mm ± 0.30) (p= 0.77). After RNA isolation, gene expression was significantly different in only a single gene out of the over 30,000 genes analyzed.
 

Conclusions: Abdominal musculature of Sprague Dawley rats at 30 days following ventral hernia formation does not show significant changes in muscle typing, biomechanical properties or gene expression as would be expected with abdominal wall remodeling. Although literature supports a rat model to investigate the disuse atrophy associated with limb muscle unloading, this does not appear to hold consistent with abdominal wall musculature. Additional models should be investigated to evaluate the abdominal wall remodeling likely associated with functional changes seen in humans who have developed ventral hernias.
 

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