What is the reason for the crack in the buttocks

Many people often say that there are cracks in their buttock groove. This condition is called anal fissure, because the anus is in the middle of the buttock groove. If the anus has cracks, it may be due to trauma, infection, excessive blood loss, prolonged redness and swelling, and lack of timely treatment. In addition, many people have dry stools for a long time, which causes damage to the anus during defecation, which leads to cracks in the buttock groove.

Pathological etiology

The exact cause of anal fissure is still unknown, but the following factors are associated with the occurrence of anal fissure:

1. Anatomical factors: The superficial part of the external anal sphincter forms the anococcygeal ligament behind the anus, which is relatively hard and has poor elasticity. Most of the levator ani muscles are attached to the sides of the anal canal, so the front and back of the anal canal are not as strong as the sides and are easily damaged. The anal canal and rectum form the anorectal angle, which makes the back of the anal canal bear great pressure from feces, etc., which are all factors that cause anal fissures.

2. Trauma: Patients with chronic constipation have dry and hard stools and may easily damage the skin of the anal canal due to excessive force when defecating. Repeated injuries can cause deep lacerations that extend through the entire layer of skin, forming chronic infectious ulcers. It has been reported that constipation causes anal fissures in 14% to 24% of cases, but constipation may also be a consequence of anal fissures due to the patient's fear of defecation. In addition, birth trauma can also cause anal fissures, accounting for about 3% to 9%. Frequent bowel movements during diarrhea can easily damage the sensitive and tight anal canal, and repeated damage can lead to chronic infectious ulcers.

3. Infection: Chronic inflammation near the dentate line, such as anal sinusitis in the posterior median area, spreads downward to cause subcutaneous abscesses, which rupture and become chronic ulcers. The reason why the anal canal is difficult to heal after injury is still unknown. Some people believe that it is mainly caused by injury combined with infection. During infection, inflammatory cells can release collagenase to prevent the regeneration and extension of epithelial tissue.

4. Ischemia Recently, some people have proposed that ischemia in the posterior midline of the anal canal is the reason why anal fissures often occur in this area, because the distal end of the anal canal is supplied by the inferior rectal artery, which passes through the ischiorectal fossa and branches out into small branches through the anal sphincter to the mucosa, but most posterior commissures lack branches of the inferior rectal artery (accounting for 85%). Capillary morphological studies also suggest that the capillaries inside the internal sphincter at the posterior midline are relatively sparse. Some people used laser Doppler blood flowmetry to measure that the blood flow at the posterior anal junction is less than that in other quadrants. All of the above indicate that ischemia is indeed the main factor in the development of chronic anal fissure.

5. Anal canal stenosis Anal canal stenosis caused by congenital malformation, trauma or surgery is more likely to be damaged and cause anal fissure when dry stool passes through.

6. Internal sphincter tension Patients with anal fissure have abnormal excessive contraction of the internal sphincter. Reflex internal sphincter spasm is currently considered to be an important reason why anal fissures are difficult to heal. The anal pressure in patients with anal fissure is significantly higher than that in normal people, reaching 127.5±42.2 kPa (956±316 mmHg), while that in normal people is only 86.3±33.3 kPa (647±250 mmHg). This high pressure can be restored to near normal after anal dilation treatment.