ABSTRACT
The human internal sphincter (IAS) has unique structural and functional characteristics. It largely contributes to the anal-high pressure zone. Due to its very specific motility, pharmacology, and innervation patterns, it is illusory to think that the IAS could be completely substituted by nonsphincteric tissue. Internal sphincter substitution could be applied in children with incontinence due to an unsuccessful repair of imperforate anus, in patients after extensive pelvic and anal trauma, as well as in adults in whom the normal transit would be restored after abdomino-perineal anorectum excision. The advantage of additional smooth muscle IAS substitution may be to provide a mass that can be compressed by the surrounding external sphincter substitute, resulting in better, i.e., hermetic, closure of a scar-free anal canal. The pyloric sphincter can be mobilized with its intact vascular supply to the perianal region. Free smooth muscle transplants have been applied in man in order to substitute for the IAS.
