Causes

There are many possible reasons to explain why a patient has an incisional hernia. These reasons may be broadly classified as mechanical factors, patient factors and technical factors.

Mechanical factors

A mechanical factor is anything that increases intra-abdominal pressure after an operation. This can lead to the development of an incisional hernia. A common reason is a postoperative ileus.  This is when the abdomen becomes distended because the intestines are not working properly after an operation.  The swelling of the intestines increases the pressure in the abdomen and places tension on the incision. The tension then leads to the breakdown of healing.  Another example is a chronic cough.  Coughing and vomiting are associated with a brief but significant increase in intra-abdominal pressure.  This, again, leads to too much tension on the incision and possible breakdown of the incision. Obviously, if a patient lifts something too heavy immediately after the operation, he or she can also tear the incision and cause a hernia.

Patient factors

Patient factors are diseases or illnesses that impair wound healing.  The three principle examples are infection, malnutrition and diabetes (sugar). 

• Infection, either in the incision or at another site, such as pneumonia, impairs wound healing. In part, this may be because sutures and tissues are destroyed by the infection.  In addition, white cells are diverted from the healing process to fight infection.
• Malnutrition leads to poor wound healing because the nutrients necessary for good healing are present in insufficient quantities or are completely absent.  Malnutrition may be a generalized condition in which proteins and energy are deficient, or a specific condition, such as lack of a specific vitamin.  Scurvy, which results from vitamin C deficiency, is an example of a deficiency in one key nutrient that leads to poor wound healing.
• Diabetes and other chronic illnesses also impair wound healing and are associated with a higher incidence of hernia formation than the general population.  Diabetes affects wound healing by impairing the function of white cells, predisposing the patient to infection and limiting the ability of new blood vessels to grow into the healing area.  Chronic illness of any type also affects wound healing through problems with nutrition and a general increase in inflammation.

Technical factors

The principle technical factor that leads to an incisional hernia is too much tension on the incision when it is closed.  This can cause the sutures to tear through the tissue when added stress is placed on it, such as during coughing or lifting.  Excessive tissue tension can also reduced blood flow to the tissue around the suture itself.  This leads to breakdown of the tissue and the suture pulls through.  Other technical factors unrelated to tissue tension may also play a role.  For example the sutures may have been placed in weak tissue, the wrong layer of tissue may have been sutured, the suture may have broken or the suture may not have been strong enough for the tension it is later subjected to.

Hernias