Surgery on the anal muscle
BMJ Group Medical Reference
Your doctor may recommend having surgery on your anal muscle if other treatments haven't helped. This operation is called an internal anal sphincterotomy, and it helps heal anal tears in about 9 in 10 people.   It's the most reliable long-term cure for anal tears.
It works better than another operation called anal stretch. 
Surgery on the anal muscle is a minor operation. It can be done while you're awake (you're given a local anaesthetic so that you don't feel pain) or while you're asleep (you're given a general anaesthetic). The surgeon will make a small cut in your anal muscle. The cut makes your muscle weaker so it's less likely to tighten up (go into spasm). This improves the blood flow to the skin of your anus and the tear is more likely to heal.
Surgery on the anal muscle can have side effects for a few weeks after surgery. About 1 in 10 people lose full control over their bowels. Doctors call this incontinence. Many people have flatus incontinence. This means they can't fully control wind coming from their anus. But these problems usually go away fairly quickly. 
The anus, which is at the end of the rectum, is where stools leave your body when you go to the toilet. Part of the anus is a muscle that helps you hold in the stool until you are on the toilet.
You may have a type of medicine called a general anaesthetic when you have surgery. It is given to make you unconscious so you don't feel pain when you have surgery.
If you have incontinence, you cannot control when you pass urine (this is called urinary incontinence) or have a bowel movement (faecal incontinence).
A local anaesthetic is a painkiller that's used to numb one part of your body. You usually get local anaesthetics as injections.
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