Levator Ani Subdivisions
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Direct answer
The levator ani is really a trio on each side — pubococcygeus with its visceral slips, puborectalis, and iliococcygeus — arising from the back of the pubic body and from the arcus tendineus, a thickened line on the fascia of obturator internus running from pubis to ischial spine. Between the two medial edges stretches the levator hiatus, through which the urethra, vagina and anal canal must pass, kept functionally closed by the puborectalis sling and the perineal muscles. Childbirth tears these subdivisions at predictable sites, and the pattern of injury — avulsion from the arcus tendineus, or stretch of the pudendal nerve — determines whether a woman later develops prolapse or incontinence.
What you must remember
- Pubococcygeus: the anteromedial part, giving visceral slips — puboperinealis to the perineal body, pubovaginalis or puboprostaticus to vagina or prostate, and puboanalis to the anal wall.
- Puborectalis: the U-shaped sling from pubic bodies around the anorectal junction, pulling it forward into the anorectal angle; the keel of continence.
- Iliococcygeus: the posterolateral sheet from the arcus tendineus to the coccyx and anococcygeal raphe; often thin and partly aponeurotic.
- Arcus tendineus of levator ani: the fibrous thickening of obturator fascia from the pubis to the ischial spine — the muscle's lateral anchorage and its common avulsion site in labour.
- Levator hiatus: the gap between the medial edges, transmitting urethra, and in the female vagina, plus the anal canal; closed in life by puborectalis, the perineal membrane and the perineal body.
- Nerve supply: the nerve to levator ani from S3 and S4 on the pelvic surface, with additional supply from below through the perineal branch of the pudendal nerve.
- Fibre type and function: fatigue-resistant slow-twitch fibres maintain constant tone, forming the levator plate that holds the pelvic organs against rises in intra-abdominal pressure.
How the floor fails in labour
Picture a vertex delivery in occiput-posterior position with a prolonged second stage. The fetal head distends the levator hiatus, stretching puborectalis and pubococcygeus over the ischial spines and the arcus tendineus. Two injuries follow. In an avulsion, the muscle tears off the arcus tendineus near the ischial spine, visible decades later on translabial ultrasound or MRI as an asymmetrical "dropout" of the muscle sling; the detached side can no longer support the vagina, and anterior and central compartment prolapse follow at several times the background rate. In a neuropathy, the same stretch injures the pudendal nerve against the sacrospinous ligament, denervating the external anal and urethral sphincters it supplies — the quiet beginning of later faecal or stress incontinence.
The subdivision anatomy explains the repair logic too: because puborectalis is the closure of the hiatus, a torn pubovisceral sling widens the hiatus permanently; pelves with a wider resting hiatus, measurable as the levator-urethral gap, are the ones that prolapse. Postnatal pelvic floor muscle training works on exactly these fibres, and an obstetric anal sphincter injury repair rebuilds the perineal body to which puboperinealis anchors.
Where students slip
Puborectalis is grouped under pubococcygeus in older texts and listed separately in newer ones — quote whichever your examiner holds, but state its sling and its fusion with the deep external sphincter accurately. The arcus tendineus of the levator ani is confused with the arcus tendineus of the pelvic fascia, a more medially placed line to which the pubocervical fascia attaches; one anchors muscle, the other fascia, and both converge on the ischial spine, the landmark of every pelvic exam. Finally, remember the levator's upper surface is pelvic peritoneum's floor, its lower surface the roof of the ischioanal fossa — the same muscle seen from two compartments.
Frequently asked questions
What are the subdivisions of levator ani?
Pubococcygeus with its puboperinealis, pubovaginalis or puboprostaticus and puboanalis slips, puborectalis, and iliococcygeus — plus coccygeus completing the pelvic diaphragm.
What is the arcus tendineus of levator ani?
A thickened band of obturator fascia from the pubic body to the ischial spine, giving origin to levator ani fibres and the usual site of avulsion during childbirth.
What passes through the levator hiatus?
The urethra in both sexes, the vagina in the female, and the anal canal, the gap being closed by puborectalis, the perineal membrane and the perineal body.
Why does puborectalis matter for continence?
It slings the anorectal junction forward, creating the anorectal angle; its contraction with the deep external sphincter forms the anorectal ring.
How is levator ani nerve supply?
From S3 and S4 on its pelvic surface through the nerve to levator ani, reinforced from below by the perineal branch of the pudendal nerve.
What is levator avulsion?
Tearing of levator ani, usually pubovisceral fibres, off the arcus tendineus at the ischial spine during vaginal delivery, detectable on imaging and strongly associated with prolapse.