Incisional Hernia Effect on Abdominal Neuromuscular Properties in the Rat

Midline hernias complicate approximately 11% of abdominal surgeries. Maladaptive changes in the abdominal neuromusculature may contribute to hernia persistence or recurrence. Both injury and denervation negatively affect muscle contractile properties immediately following muscle lesion, but it is unclear whether abdominal muscles are affected once wound healing has stabilized (after 28 days). The authors studied the contractile properties of specific abdominal muscles and subsequently immunohistologically labeled the muscles for fiber denervation. They hypothesized that, compared with sham-operated animals, abdominal muscles from rats with an abdominal hernia have a reduced capacity to produce force and exhibit a population of denervated muscle fibers. Additionally, since skeletal muscle weakens and muscle fiber denervation increases with increased age, they tested the interaction effect of age with surgery.

Adult (8-month-old, n = 7) and old (25-month-old, n = 9) rats were assigned to a sham or hernia surgical group. A 3 × 5-cm skin flap was made in the abdomen for all rats. A 6-cm incision was cut through the linea alba and left unclosed in the hernia group. The skin was closed in both groups. Recovery proceeded for at least 28 days, when strips of rectus abdominis and external oblique muscles were removed for in vitro contractile specific force measurements (force normalized to cross-sectional area) and histological processing.

GLM statistical results indicated that both hernia surgery and old age had significant negative effects on muscle specific force. There was no significant interaction between the effect of the hernia surgery and the effect of age. Immunohistology showed clusters of denervated fibers in the hernia group muscles.

Hernia surgery and increased age are significant detriments to abdominal muscle contraction. Increased numbers of denervated muscle fibers are associated with these effects.