De-hong Yu and Hei-ying Jin
Defecation is a complicated procedure in which pelvic floor muscles actively participate in the process. Rectal distention evokes the desire to defecate and induces relaxation of the anal sphincter. Under conducive circumstances, the act of defecation is completed by adoption of a suitable posture, contraction of the diaphragm and abdominal muscles to increase the intraabdominal pressure, and relaxation of the two striated muscle of the puborectalis and external anal sphincter. Puborectalis relaxation allows widening and lowering of the anorectal angle. Coordination between abdominal contraction and pelvic floor relaxation is crucial to this process (Fig. 26.1).
The puborectalis muscle is the most important component of the levator mechanism relating to continence and defecation. This muscle originates from the inferior border of the pubis and the superior fascia of the urogenital diaphragm, and slings around both sides of the rectum to exert a pull and create the anorectal angle. If the puborectalis muscle cannot relax or even contracts during defecation, the anorectal angle will not change or may even decrease, defecation will be difficult, and constipation can ensue.1,2 In 1964, Wasserman3 termed this syndrome "puborectalis syndrome," which is characterized by difficult and painful defecation and, occasionally, the inability to defecate for several days. On the basis of pathologic findings that have shown marked hypertrophy of the muscle fibers, this type of anorectal stricture was known due to spasmodic hypertrophy of the puborec-talis muscle. The main causes of puborectalis syndrome are paradoxical puborectalis contraction (PPC) and puborectalis hypertrophy (PH). When PPC is a functional disorder, it is also known as spastic pelvic floor syndrome or pelvic outlet obstruction. In patients with PPC, the structure of the puborectali muscle is normal but the puborectalis muscle cannot properly relax and contract.4 Therefore, the ideal treatment should aim at restoring the normal pub-orectalis function rather than at removing normal tissue.5
Jorge et al6 reported that the mean success rate for biofeedback for constipation was 68.5%, attributable to paradoxical puborectalis syndrome. Other nonsurgical methods, such as bot-ulinum toxin injection and anal dilation, can also offer improvement to some patients with PPC who do not respond to biofeedback.7,8 Another, often neglected cause of puborectalis syndrome is PH. The etiology of PH is unclear. The most common cause may be due to inflammation around the puborectalis, which causes puborectalis edema and stimulates hypertrophy. Gradually, the puborectalis loses its elasticity and cannot contract and relax func-tionally.9,10 The authors reviewed 200 cases of PH and found sepsis around the puborectalis in 15% to 30%.9 Other factors such as congenital trauma and chronic diarrhea may also play a role in the development of PH. The structure of the pub-orectalis is abnormal among patients with PH. Successful treatment cannot rely on biofeedback and other conservative methods, but does respond favorably to segmental excision of the puborectalis muscle.
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