Why Do Hernias Occur?

A hernia is formed by the protrusion of part of the abdominal contents (usually fat or bowel) through a defect or weakness in the abdominal wall.

Basically the abdominal wall has been modified at particular sites to developmental requirements. Hernias almost exclusively occur at these well recognised sites of weakness.

All hernias occur at the site of a structural weakness in the abdominal wall – that is where the 3-layer muscle structure of the abdominal wall has been modified developmentally and anatomically. In the case of the umbilical region and epigastrium the fascia has fused into 1-layer, in the midline of the abdomen wall. As shown in A and B – representing mid-line hernias such as an epigastric hernia or umbilical hernia.

These diagrams show the general structure of the abdominal wall. They show the 3 main muscles in brown. These muscles fuse and form a large aponeurotic tendon sheet (termed the rectus sheath) and this encloses a single strap-like muscle – the rectus abdominis muscle – the rectus sheath fuses in the midline to form the linea alba (white). Because there is a single layer here, this is a potential weakness and thus a common site where hernias develop – termed ‘epigastric’ hernias.

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The commonest site for hernias is the groin. In the groin there are 2 types of hernias – inguinal and femoral. The femoral is lower and relatively rare. It occurs more frequently in females.

The INGUINAL hernia, which is by far the most common, occurs at any age. The descent of the testes and its cord through the muscle wall of the groin into the scrotum at birth has left a potential weakness through which the hernia descends. Any activity which then constantly or suddenly increases intra-abdominal pressure or weakens the muscle, may cause a hernia eg, cough, constipation, bladder obstruction or heavy lifting. Ageing weakens the muscles. Obesity increases both the intra-abdominal pressure and reduces the muscle strength.