Origins and Insertions
The levator ani forms the main part of the pelvic diaphragm, the cranial layer of the pelvic floor. It is made up of the following three muscles:
- Puborectalis muscle: originates lateral from the symphysis on both sides and encircles the rectum (anorectal junction) which causes a ventral bend between rectum and anal canal. Partly it is interwoven with the external anal sphincter.
- Pubococcygeus muscle: runs from the pubic bone (lateral of the origin of the puborectalis muscle) to the tendinous center of the perineum, anococcygeal body and tailbone. In men, medial muscle fibers are partly connected to the prostate.
- Iliococcygeus muscle: extends more laterally from the fascia of obturator internus muscle to the tailbone. As a whole the levator ani builds a V-shaped structure. Both levator arms limit a triangle opening (levator hiatus) which is divided by prerectal fibers into the urogenital hiatus (ventral) and anal hiatus (dorsal). The urogenital hiatus is the pathway for the urethra and, in women, the vagina. The rectum runs through the anal hiatus.
It is primarily supplied by direct branches of the sacral plexus (S3-S5). To a small degree the pudendal nerve contributes to its innervation as well.
Through its tonic activity, the levator ani stabilizes the abdominal and pelvic organs on the one hand and controls the opening and closing of the levator hiatus on the other hand.
While in quiescent state, the urethra and the rectum are mechanically closed at the levator hiatus. The muscle relaxes at the beginning of urination and defecation. By this means the levator ani muscle plays a crucial role in the preservation of urinary and bowel continence.
The levator hiatus is a potential weak spot of the pelvic floor musculature, especially in women. Through increased intra-abdominal pressure (e.g. pregnancy, obesity or even chronic cough) the pelvic floor can be impaired and damaged in the long term. This may cause a descent of the perineum (descending perineum syndrome, DPS) up to a complete prolaps of the vagina or rectum. Consequences are urinary and bowel incontinence.
Approximately 6% of the population suffer under intermittent painful muscle spasms of the levator ani (levator ani syndrome). These can occur at any time and are often accompanied by a feeling of pressure and tension in the anorectal region. To this day the etiology remains unclear. Both neuralgia of the pudendal nerve and psychosomatic components are in discussion.