The puborectalis is the deepest component of the levator ani and the most important muscle for maintaining faecal continence through the flap valve mechanism of the anorectal angle. Its U-shaped sling around the anorectal junction pulls it forward at the level of the pubis, creating the acute anorectal angle that forms a flap valve preventing stool from entering the anal canal until voluntary relaxation occurs. Paradoxical puborectalis contraction during attempted defaecation produces obstructed defaecation syndrome.
| Origin | Pubic body bilaterally (lower part of the pubic symphysis) |
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| Insertion | Loops posteriorly around the anorectal junction without inserting on a bone, creating the anorectal sling |
| Nerve Supply | Direct branches from S3 and S4, and the inferior rectal nerve |
| Blood Supply | Internal pudendal artery |
| Actions | Maintains the anorectal angle (approximately 80-90 degrees at rest) by pulling the anorectal junction forward; Relaxes during defaecation to straighten the anorectal angle and allow stool passage; Contracts voluntarily to defer defaecation (increases the anorectal angle) |
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The anorectal angle produced by the puborectalis sling is the primary continence mechanism for solid stool — the sharper the angle, the greater the mechanical barrier. Relaxation during straining must occur for normal defaecation to proceed, and failure of this relaxation (anismus) produces severe obstructed defaecation.
Puborectalis avulsion from childbirth produces loss of the anorectal angle and pelvic floor descent, contributing to both stress urinary and faecal incontinence. Levator avulsion is detected on MRI as absence of the normal muscle attachment to the pubic bone. Biofeedback therapy for anismus (paradoxical puborectalis contraction) uses EMG feedback to train the patient to relax the puborectalis during defaecation straining.
Puborectalis is assessed by digital rectal examination as the anorectal sling felt posterolaterally at the anorectal junction, with the patient asked to squeeze (contraction) and strain (relaxation) to assess the voluntary control of the sling.
Childbirth disruption of the pubic insertion producing widened levator hiatus, pelvic organ prolapse, and faecal incontinence from loss of anorectal angle support.
Paradoxical puborectalis contraction during defaecation producing obstructed defaecation syndrome, managed with biofeedback therapy and botulinum toxin injection.
