LIS stands for lateral internal sphincterotomy, a minor surgical procedure used to treat chronic anal fissures that haven’t responded to other treatments. It works by making a small cut in the ring of muscle that controls the anus, reducing the excess tightness that prevents the fissure from healing. The procedure has a success rate of about 94% to 96%, making it the most effective treatment available for fissures that won’t heal on their own.
Why the Procedure Is Needed
An anal fissure is a small tear in the lining of the anal canal. Most fissures heal with basic care: more fiber, more water, warm baths, and topical treatments. But in some people, the internal anal sphincter (the muscle that keeps the anus closed at rest) stays too tight, cutting off blood flow to the tear and preventing it from closing. When a fissure persists despite at least six weeks of conservative treatment, it’s considered chronic, and surgery becomes the next step.
The hallmark symptoms are moderate to severe pain during bowel movements and small amounts of blood on the toilet paper. The pain typically lingers for 15 to 30 minutes after each bowel movement, which is what drives most people to seek treatment. Candidates for LIS need to have good bowel control before the procedure, since the surgery slightly loosens the sphincter muscle.
How LIS Surgery Works
The goal is simple: release just enough of the internal sphincter muscle to lower the resting pressure inside the anal canal. With less pressure, blood flow returns to the fissure and it can finally heal. The surgeon divides roughly one-half to one-third of the internal sphincter through a small incision, usually about 1 centimeter long, made on the side of the anus rather than directly over the fissure itself.
There are two techniques. In the open method, the surgeon uses a retractor to directly see the sphincter muscle, separates the muscle fibers from the surrounding tissue, and then cuts the targeted portion under direct vision. In the closed method, the surgeon identifies the muscle by feel, inserting a finger into the anal canal to guide a blade through the skin. Both approaches produce similar healing and recurrence rates (around 2% to 3%), but the open technique has shown a lower risk of incontinence because the cut is more precisely controlled. One comparative study found zero incontinence cases in the open group, while 5% of patients in the closed group experienced some degree of gas or fecal leakage.
Success Rates and Recurrence
LIS is the gold standard for chronic anal fissures precisely because it works so reliably. Conventional LIS heals fissures in about 94% of patients. A tailored version of the procedure, where the length of the cut is matched to the length of the fissure, has reported success rates as high as 99.6%. A newer “minimal” approach, which cuts even less of the muscle, achieved a 96% complication-free healing rate with a recurrence rate of just 1.3%.
Recurrence after any version of LIS is uncommon, generally falling between 1% and 3%. When fissures do come back, they can often be treated with a repeat procedure or with non-surgical options.
LIS vs. Botox Injections
Botulinum toxin (Botox) injections offer a non-surgical alternative. The injection temporarily paralyzes the sphincter muscle, achieving a similar pressure reduction without a permanent cut. It’s easier to perform and avoids the small risk of lasting incontinence.
The tradeoff is effectiveness. In one head-to-head study, all patients who had LIS surgery had healed fissures at the six-month mark, compared to about 80% in the Botox group. The recurrence rate at six months was 7% for surgery versus 20% for Botox. Botox also left more patients with ongoing pain and bleeding at follow-up. Still, because it carries about a 60% chance of full cure with a simple injection, many clinicians recommend trying Botox first before moving to surgery.
Risks and Possible Complications
The most talked-about risk is incontinence, since the surgery permanently divides part of the muscle responsible for bowel control. In practice, solid stool incontinence is extremely rare. A five-year follow-up study from a high-volume center found that no patients lost control of solid stools. About 2% experienced occasional leakage of liquid stool, and 24.5% reported some difficulty controlling gas. Up to 39% of patients notice transient incontinence in the weeks after surgery, but these symptoms typically resolve within six to eight weeks as the area heals.
Other complications are uncommon. In a large retrospective study of over 700 patients, postoperative bleeding occurred in 0.7%, abscess formation in 0.3%, and hematoma in 0.2%. Overall, wound-related complications like bleeding, abscess, or a non-healing wound affect roughly 3% of patients.
Recovery After Surgery
Most people notice that the intense pain from their fissure improves within a few days of the procedure. The surgical site itself takes about six weeks to fully heal, but most people return to work and normal activities within one to two weeks.
During recovery, warm soaking baths are the single most effective tool for managing discomfort. Soaking in plain warm water for at least 20 minutes, three times a day, helps with pain and keeps the area clean. There’s no upper limit on how long or how often you can soak. After each bowel movement, gently rinse the area with water or take a quick bath.
Keeping stools soft is critical to protecting the healing tissue. A fiber supplement taken daily, combined with six to eight glasses of water or non-caffeinated fluids, helps prevent straining. A stool softener is also recommended for as long as you’re taking prescription pain medication, since those medications can cause constipation. The dressing placed during surgery comes off the morning after, typically right before your first soak.