"" Regional Variation in the Histomorphology and Tensile Strength of the Ventral Rectus Sheath in the Male Goat (Capra Hircus)

Research Article

Austin J Anat. 2015;2(2): 1036.

Regional Variation in the Histomorphology and Tensile Strength of the Ventral Rectus Sheath in the Male Goat (Capra Hircus)

Odula PO¹*, Hassanali J¹ and Kiama SG²

¹Department of Human Anatomy, University of Nairobi, Kenya

²Department of Veterinary Anatomy and Physiology, University of Nairobi, Kenya

*Corresponding author: Odula PO, Department of Human Anatomy, University of Nairobi, P.O. Box 25540- 00603 Nairobi, Kenya

Received: May 18, 2015; Accepted: July 14, 2015; Published: July 18, 2015

Abstract

The ventral rectus sheath (VRS) plays a key role in the stabilization of the ventral abdominal wall. This sheath has to be particularly strong in ruminants to accommodate the viscera and the large quantities of forage in their stomach. This study was conducted to establish the structural and the mechanical properties of the ventral rectus sheath in the goat, a browser, in order to elucidate its function. The ventral rectus sheath was formed by superficial and deep lamina consisting of obliquely aligned collagen fibers derived from the external and internal oblique abdominal aponeuroses respectively. Closely apposed and intimately held to the superficial lamina was a layer of longitudinally aligned elastic fibers, the ttunica flava abdominis or modified deep fascia. This tunica flava abdominis progressively increased in thickness from the epigastrium to the hypogastrium. On tensiometry, the epigastric ventral rectus sheath withstood about half the load (50N/mm2) required to reach yield point compared to the umbilical ventral rectus sheath (94.5N/mm2). Furthermore, the Youngs modulus showed that the umbilical ventral rectus sheath was the stiffest at 669 (SD 22.2) N/mm2 while the epigastric ventral rectus sheath was the weakest at 554 (SD 29) N/mm2 respectively when exposed to longitudinal traction. In conclusion, the progressively thickening of the tunica flava abdominis and the superficial lamina from the epigastrium to the hypogastrium may confer reversible stretch ability and strength to the ventral rectus sheath and is therefore well suited for longitudinal load strength needed to support the compound stomach during browzing.

Keywords: Goat; Ventral rectus sheath; Collagen fibers; Tunica flava abdominis; Elastic fibers; Tensile strength

Abbreviations

LA: Linea Alba; EM: External Oblique Abdominis Muscle; RM: Rectus Abdominis Muscle; VRS: Ventral Rectus Sheath; EVRS: Epigastric Ventral Rectus Sheath; UVRS: Umbilical Ventral Rectus Sheath; HVRS: Hypogastric Ventral Rectus Sheath; PS: Pubic Symphysis; XP: Xiphoid Process; DF: Deep Fascia; SL: Superficial Lamina; DL: Deep Lamina

Introduction

The ventral abdominal wall is formed by the aponeurotic tendon of the abdominal wall muscles. The aponeuroses wrap the rectus abdominis muscle before forming the linea alba ventrally. The aponeuroses wrapping the rectus abdominis muscle ventrally is termed the ventral rectus sheath. It plays a key role in the stabilization of the ventral abdominal wall [1]. This tough tendinous structure is formed by the interlocking aponeurotic fibers of the external oblique abdominis and the superficial lamellae of the internal oblique abdominis [2,3]. In herbivores, the ventral rectus sheath is reinforced by the tunica flava abdominis which is part of the deep fascia of the trunk [4].

Ruminants like the goat, have a stomach capacity which is capable of accommodating large quantities of forages causing marked abdominal distension. Furthermore, goats have the ability to stand on their hind legs for long periods and sometimes can even climb in order to reach parts of trees they prefer for browsing [5]. Studies on the human ventral rectus sheath provided insights into its biomechanical structure [1,6]. However, apart from the macroscopic work done by Walmsey, the structure of the ventral rectus sheath of the goat is largely unknown [2]. This is despite the fact that the ventral abdominal hernias are fairly common in goats [7,8]. For instance, retrospective studies by Abdin-Bey and Ramadan reported a prevalence rate of ventral abdominal hernias of more than to 88% in adult goats who presented with hernia swellings [9].

The aim of this study is to describe the histomorphology of the ventral rectus sheath and evaluate its tensile strength in the goat. This may explain how the ventral rectus sheath of the goat, as a quadruped grazer and browser, is adapted to its function.

Materials and Methods

The ventral abdominal wall was harvested from 1- 2year old 6 (six) healthy male goats (Capra hircus) weight range 10-13kg. The goats were procured from a local butchery immediately after slaughter.

The skin and fascia were incised along a midline abdominal incision to form skin flaps that exposed the anterior abdominal wall aponeuroses. The xiphoid process, the umbilicus, and the pubic tubercle were used as landmarks. Using a metal template (40mm x 20mm), pieces of the ventral rectus sheath were resected from the mid-epigastric (EVRS), the umbilical (UVRS) and mid- hypogastric (HVRS) (Figure 1).