Postpartum biomechanical adaptations of the anterior abdominal wall in a rat model: Implications for diastasis rectus abdominis.

Abstract

BACKGROUND: The linea alba (LA) is a fibrous connective tissue structure that joins the rectus abdominis muscles and contributes to the mechanical integrity of the abdominal wall. Physiological changes during pregnancy can disrupt this structure. As fetal growth increases intra-abdominal pressure, the inter-rectus distance widens due to stretching of the anterior abdominal wall and LA. When this widening becomes substantial, it can result in diastasis rectus abdominis (DRA). The purpose of this study was to characterize postpartum biomechanical changes in the central anterior abdominal wall, with a focus on tissue samples containing the LA, using a rat model. METHODS: Five 3-day postpartum, five 8-week postpartum, and ten age-matched nulliparous Sprague-Dawley rats were tested. Three 7.5 × 7.5 mm samples were dissected from the central anterior abdominal wall: one at the level of the umbilicus, one cranial, and one caudal to the umbilicus. Samples underwent tensile mechanical testing at a rate of 0.5%/s until failure. Six additional rats (three nulliparous and three 3-day postpartum) were used for histological analysis. FINDINGS: Yield stress and maximum stress were significantly higher in samples from 3-day postpartum animals compared to both nulliparous and 8-week postpartum animals. Histological analysis showed increased connective tissue between the rectus abdominis muscles in the 3-day postpartum group relative to nulliparous animals. INTERPRETATION: These findings indicate substantial anterior abdominal wall remodeling following pregnancy, including increased strength and stiffness in the early postpartum period. Alterations in this remodeling response may reduce abdominal wall load-bearing capacity and increase susceptibility to inter-rectus separation, as observed in DRA.