The tear often exposes the muscle around the anus, called the anal sphincter. The damage can cause that muscle to spasm, which can pull apart the edges of the fissure even more. The spasms can cause pain and slow down the healing. Bowel movements can also keep the fissures from getting better.
It is possible that the main title of the report Hirschsprung's Disease is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.