Lateral Subcutaneous Internal Sphincterotomy (LSIS) is a surgical procedure primarily used to treat chronic anal fissures that have not healed with conservative treatments. It involves making a small incision in the internal anal sphincter muscle to relieve pressure and reduce the spasm that causes pain in the anal canal. By cutting a portion of the sphincter, the procedure helps to improve blood flow to the area and promotes healing of the fissure. While the procedure is effective for relieving pain and promoting healing, it is performed carefully to avoid potential complications, such as incontinence. LSIS is often recommended when other treatments, such as medications or topical ointments, have failed. It is a safe and widely used method to address persistent anal fissures and provides long-term relief for patients.