Levator ani

Musculus levator ani

Also known as: pelvic diaphragm, pelvic floor, puborectalis, pubococcygeus, iliococcygeus

A broad, funnel-shaped muscular sheet that, with coccygeus, forms the pelvic diaphragm. It supports the pelvic organs, maintains faecal and urinary continence and resists rises in intra-abdominal pressure.

Overview

Levator ani arises from the body of the pubis, the tendinous arch of levator ani (a thickening of the obturator internus fascia) and the ischial spine. It slopes down and medially to the perineal body, the walls of the prostate or vagina, the rectum and anal canal, the anococcygeal body and the coccyx. It has three parts.

- Puborectalis: a U-shaped sling around the anorectal junction that pulls it forward, creating the anorectal angle (≈90°) that is vital for faecal continence. It relaxes during defecation.
- Pubococcygeus: the main part, with subdivisions (pubovaginalis or puboprostaticus, puboperinealis, puboanalis) that support the viscera.
- Iliococcygeus: a thin posterolateral sheet from the tendinous arch to the coccyx and anococcygeal body.

The urogenital hiatus between the medial borders of the two levators transmits the urethra (and the vagina in females). The levators show constant tonic activity and contract reflexly when intra-abdominal pressure rises (coughing, sneezing, lifting), supporting the pelvic viscera and helping to close the urethra and anorectum.

Location

Floor of the pelvic cavity, separating it from the perineum (ischio-anal fossae below).

Parts & subdivisions

Puborectalis

Sling around the anorectal junction, producing the anorectal angle. Essential for faecal continence.

Pubococcygeus

From the pubis to the coccyx and anococcygeal body. Supports the prostate or vagina, the perineal body and the anus.

Iliococcygeus

From the tendinous arch and ischial spine to the coccyx and anococcygeal body.

Coccygeus

The posterior part of the pelvic diaphragm.

Anatomy

Origin

Body of the pubis, tendinous arch of the obturator fascia and the ischial spine.

Insertion

Perineal body, walls of the prostate or vagina, rectum and anal canal, anococcygeal body and the coccyx.

Action

Supports and raises the pelvic floor; resists intra-abdominal pressure; maintains the anorectal angle (puborectalis).

Innervation

Nerve to levator ani (direct branches of S4), inferior anal (rectal) nerve and perineal branches of the pudendal nerve (S2–S4), and the coccygeal plexus.

Nerve roots

S2–S4 (mainly S3–S4)

Arterial supply

Inferior gluteal, internal pudendal and inferior vesical arteries (branches of the internal iliac artery).

Relations

Superior surface: pelvic fascia, bladder, rectum, prostate or uterus and vagina. Inferior surface: ischio-anal fossae and the perineum.

Clinical significance

Childbirth injury and pelvic organ prolapse

Vaginal delivery can stretch or avulse pubococcygeus and puborectalis and damage the pudendal nerve. This leads to cystocele, rectocele and uterine prolapse, and to stress urinary and faecal incontinence. Pelvic floor muscle training (Kegel exercises) is first-line treatment.

Anorectal angle

Failure of puborectalis to relax on straining (dyssynergic defecation, anismus) causes obstructed defecation. Loss of the angle contributes to faecal incontinence.