An anal fissure is a break, tear or open sore in the lining of the anal canal. The anal canal is the last part of the large intestine, located between the rectum and the anus, through which your stools are passed. A tear in the lining of the anal canal is called an anal fissure which can have a number of possible causes.

The most common cause of anal fissures is damage to the lining of the anal canal or anus.

Constipation can be a contributory factor - most cases of anal fissure occur when a particularly hard or large stool tears the lining of the anal canal.

 Anal fissures can also be caused by:

• recurring diarrhoea
• inflammatory bowel disease (IBD), for example Crohn's disease and ulcerative colitis
• pregnancy and childbirth
• rarely, a sexually transmitted infection (STI), such as syphilis or herpes, which can damage the anal canal
• tight anal sphincter muscles can increase tension in your anal canal, making you more prone to anal fissures.

The operation aims to prevent the sphincter going into spasm, so restoring normal blood supply to the anal canal, helping the anal fissure to heal and reducing the chance of developing more fissures.

Lateral sphincterotomy has a very good rate of success in treating anal fissures.

You may have been recommended to have lateral sphincterotomy if you have already had non-surgical treatment for anal fissures, whether acute or chronic (those lasting six weeks or more). Anal fissures typically heal within a few weeks without any treatment. However, if they're caused by constipation that remains untreated, they can recur.

During a lateral sphincterotomy a small cut is made in the ring of muscle (sphincter) around the anal canal. This reduces tension in the anal canal, allowing the anal fissure to heal. 

It is a relatively quick and simple procedure normally carried out under a general anaesthetic. This means you'll be asleep while the operation is carried out but you’ll usually be allowed home later the same day.

Some discomfort is to be expected and we’ll give you painkillers to relieve any pain. You may be advised to make some dietary changes and perhaps take some laxatives to avoid becoming constipated and to make your stools easier to pass.

You will probably have a dressing on your wound which may need be changed daily. We’ll make all the arrangements for this to happen before you go home.

You’ll need to take some time off work and should avoid strenuous exercise until advised. You should be fully healed within two to four weeks and, in most cases, the anal fissure will not return.

A lateral sphincterotomy is usually very effective in treating anal fissures, although in a few cases they do return. Some people will experience some temporary bowel incontinence because of damage to the anal muscles. However, this is usually just wind incontinence which only lasts a few weeks.