A hernia is the protrusion of a small loop of intestine through an inner muscle wall. The most common variety is the inguinal hernia, where a small loop of intestine protrudes through the inguinal canal in the groin as a result of excessive internal pressure, coughing or strain. They are more common in men, who have more than one chance in four of suffering from such a hernia at some point in their life. In contrast, women are more likely to suffer from a femoral hernia, where a section of bowel forces its way through the relatively weak muscle ring at the femoral canal, at the top of the thigh.

With a hiatus hernia, part of the stomach slips upwards into the chest area through the aperture in the diaphragm.

Most hernias are ‘reducible’ - they will become smaller due to the effects of gravity or gentle pressure and cause no problem. But when the protruding gut becomes stuck in the abdominal wall, the bowel could then become ‘strangulated’, where the blood supply is cut off. Symptoms include nausea, vomiting and severe pain. If left untreated, a strangulated hernia can lead to gangrene of the trapped bowel section.

What does the surgery involve? A hernia operation attempts to ‘patch’ up the abdominal wall by using either the patient’s own body tissue or a piece of prosthetic material, such as polypropylene mesh. This patch is sewn in via:

* open surgery, such as the Lichtenstein operation, the most common type of open mesh operation

* laparoscopy, or keyhole surgery. In this case, three small incisions are made, through which are threaded a tiny fibreoptic cable and camera lens along with various surgical instruments; the surgeon is then guided by the images transmitted to a video monitor. Keyhole hernia repair is considerably more complicated than open surgery, taking about three times as long and requiring greater technical skill from the surgeon.

What doctors don’t tell you There is no doubt that surgical techniques to correct hernias have improved dramatically over the past 10 years. The old method of open surgery, which involves placing sutures (stitches) in the abdominal wall, often requires a repeat operation because, in a large percentage of cases, the stitches come apart. Such a ‘recurrence’ may affect one-fifth of all cases, rising to 50 per cent after the third operation. Doctors maintain that the open mesh (Lichtenstein) operation has reduced the recurrence rate to only 2-5 per cent of all patients.

Nevertheless, there are still many hidden issues:

* Surgery may not be necessary. The dangers of leaving a groin hernia alone are vastly overplayed and surgery vastly overprescribed. A study by surgeons at the University College and Middlesex School of Medicine in London put the strangulation rates for inguinal hernia at 2.8 per cent a year, rising to 4.5 per cent after two years. The rate of complications rises more steeply within the first three months of hernia onset, which suggests that if you have a new hernia, you are at a greater risk of complications than someone who has had one for years (Br J Surg, 1991; 78: 1171-3).

* Your doctor can make a mistake and cause injury. Misplaced staples or overzealous cutting in all types of hernia surgery can cause permanent injury of nerves in the thigh.

* Blood clots, groin seromas (a collection of fluid), and problems of the spermatic cord or testicles may also occur.

* The stitches can give way, thereby requiring a repeat operation. Despite the more positive much-touted figures, a recent study put recurrence rates at 10 per cent among laparoscopies and 5 per cent for open surgery (N Engl J Med, 2004; 350: 1819-27).

* Complications are more frequent than initially thought. The above-mentioned study had a complication rate of an alarming 40 per cent in the laparoscopic group and 33.4 per cent in the open-surgery group.

* Keyhole repair is very risky. As the doctor, like a videogames player, is being guided via a videoscreen, it’s easy to miss; needle and other instrument injuries are common, including bladder perforation, respiratory problems, vascular injury, major haemorrhage and intestinal obstruction.

* Injury to the bowel can be fatal. A study of 90 patients who had undergone keyhole surgery for their hernia recorded four incidents of bowel injury (4.4 per cent). Of these patients, one developed sepsis (overwhelming infection) and multi-organ failure, and died. Other studies have reported death rates of 0.6-3.4 per cent - which means that, out of every 100 patients, more than three could die (Hernia, 10 March 2004; e-published ahead of print).

* Open surgery can leave the patient with persistent pain. In a study of 142 men, pain persisted for more than three years in 4 per cent of them (Hernia, 2003; 7: 185-90).

* Surgery may result in numbness or pain during sex. Up to 9 per cent of patients suffer numbness, while others have shooting pains during ejaculation (Hernia, 2003; 7: 185-90). The operation has also led to testicular atrophy.

* The long-term effects of having a foreign material in your body are still not known. There are, as yet, no studies into the long-term effects of the polypropylene mesh used in open mesh surgery. Indeed, the surgeon who developed mesh repair in Europe restricted its use to the over-50s because of the unknown long-term fate and side-effects of the prosthetic mesh implants (Lancet, 1994; 344: 375-9).

The use of surgery is usually justified for a femoral hernia. If left untreated, more than a fifth of all such hernias will strangulate after three months, and nearly half after 21 months. Indeed, some 40 per cent of sufferers are admitted to hospital as emergencies (BMJ, 2004; 328: 59-60).

Michelle Clare