Another study found that, while glyceryl trinitrate was successful in 70 patients with either chronic or acute fissures, higher doses did not speed the healing - and many of the patients had recurring fissures afterwards, and complained of headaches during the treatment (Gut, 1999; 44: 727-30).

Fissure recurrence was further highlighted in another study of 43 patients: 22 used nitroglycerin and 21 had surgery. Nearly 80 per cent of those given nitroglycerin reported headaches, and most of the chronic sufferers had a recurrence (Tech Coloproctol, 2001; 5: 143-7).

It also seems not to work on children. One study tested it against placebo and, perhaps surprisingly, pain reduction was similar in both groups, suggesting that time might be as much of a healer as the ointment (Arch Dis Child, 2001; 85: 404-7).

Another ointment, isosorbide dinitrate, was tried on 16 chronic-fissure sufferers. Although all reported mild, transient headaches, pain from the fissures stopped within three weeks in all cases. After three months of treatment, the fissures had healed in all but one case (Ned Tijdschr Geneeskd, 1995; 139: 1447-9).

The latest treatment uses botulinum toxin (botox) injections. This bacterial toxin - usually responsible for food poisoning - causes muscle paralysis. Botox is injected into the anal sphincter muscle. Early data suggest that the therapy improves symptoms in 80 per cent of patients. No long-term data are yet available.

One study found botox to be more effective than topical nitroglycerin as an alternative to surgery. Fifty patients were given either botox or a six-week course of nitroglycerin ointment. After two months, the fissures were healed in 24 of 25 patients given the injection vs 15 of the 25 using the ointment. Five patients in the ointment group stopped because it was causing moderate-to-severe headaches whereas none of the botox group reported any side-effects (N Engl J Med, 1999; 341: 65-9).

Similarly, in a study of 40 patients with chronic fissures, most reported pain relief within a few days of the botox injections, which continued for six months (Gastroenterol Hepatol, 1999; 22: 163-6). The only adverse reaction with botox was reported in a study of 20 patients with chronic fissures, where two people had transient, mild incontinence (Dig Dis Sci, 1999; 44: 1588-9).

A new ointment containing diltiazem has shown success in treating anal fissures. Tested on 71 patients for 2-16 weeks, 75 per cent reported healing after two to three months of treatment (Br J Surg, 2001; 88: 553-6).

Your doctor may prefer a more interventionist treatment. In acute cases, an anal dilator, lubricant and local anaesthetic may be tried twice daily by the patient at home, or the doctor may dilate the anus using his fingers while the patient is under a general anaesthetic. However, this procedure can cause incontinence for 7-10 days.

For fissures that won’t heal, surgery is usually required. One involves disruption of the internal anal sphincter muscle, causing a reduced pressure in the anal canal. This is supposed to prevent fissures from forming by improving blood flow to the anus. With surgery, the fissure heals in one to four weeks and remains healed in 95 per cent of cases. Incontinence can result in 15 per cent of patients.

These procedures, which include lateral anal sphincterectomy or dorsal fissurectomy and sphincterectomy, involve cutting away the internal anal sphincter. The latter procedure is generally reserved for very bad cases of chronic fissures.