Levator Ani

1. Overview

The levator ani is a broad, thin muscle group that forms the majority of the pelvic diaphragm, which supports the pelvic organs and separates the pelvic cavity from the perineum. It plays a vital role in maintaining continence, supporting pelvic viscera, and aiding in childbirth. The levator ani is a key component of the pelvic floor and works in coordination with other pelvic muscles and ligaments.

2. Location

The levator ani is located in the pelvic floor, forming a muscular sheet that spans the inner surface of the lesser pelvis:

• Superiorly: Bounded by the pelvic cavity and pelvic organs (e.g., bladder, rectum, uterus).

• Inferiorly: Borders the perineal region.

• Medially: Meets the contralateral muscle at the midline (anococcygeal raphe).

• Lateral attachments: Extends from the inner surface of the pubic bone and tendinous arch of the obturator fascia to the coccyx and sacrum.

3. Structure

The levator ani is not a single muscle but a group of muscles composed of three main parts:

• Pubococcygeus: Arises from the pubis and inserts on the coccyx and anococcygeal ligament; often subdivided further (e.g., puborectalis, pubovaginalis/puboprostaticus).

• Puborectalis: Forms a U-shaped sling around the rectum, important for fecal continence.

• Iliococcygeus: Originates from the ischial spine and tendinous arch; inserts into the coccyx and anococcygeal raphe.

Additional details:

• Innervation: Mainly from the nerve to levator ani (S3–S4), with contributions from the pudendal nerve and inferior rectal branches.

• Blood supply: Inferior gluteal artery, internal pudendal artery, and inferior vesical/vaginal arteries.

4. Function

The levator ani performs multiple vital functions:

• Supports pelvic organs: Acts like a hammock to support the bladder, rectum, uterus, and prostate.

• Maintains continence: Contracts to maintain urinary and fecal continence, especially during increased intra-abdominal pressure (e.g., coughing or sneezing).

• Assists childbirth: Helps guide the fetal head during labor and supports the birth canal.

• Facilitates defecation: The puborectalis part maintains the anorectal angle and relaxes during defecation.

5. Physiological role(s)

Beyond its mechanical role, the levator ani contributes to important physiological processes:

• Pelvic stability: Helps maintain posture and core stability by supporting the pelvic viscera and resisting downward forces.

• Intra-abdominal pressure regulation: Works with the diaphragm and abdominal muscles during activities such as lifting, straining, or coughing.

• Sexual function: Supports erectile function and orgasm through pelvic floor contractions in both males and females.

• Lymphatic and venous return: Assists venous and lymphatic drainage from the pelvic organs through rhythmic contraction and relaxation.

6. Clinical Significance

The levator ani is associated with several important clinical conditions:

• Pelvic organ prolapse:

  • Weakness or tearing of the levator ani (especially during childbirth) can lead to prolapse of the bladder, uterus, or rectum into the vaginal canal.

• Urinary and fecal incontinence:

  • Dysfunction or denervation of the levator ani can compromise continence mechanisms, especially in aging or post-surgical patients.

• Levator ani syndrome:

  • Characterized by chronic pelvic pain, pressure, or aching due to muscle spasm or tension, often mistaken for rectal or urogenital disease.

• Childbirth trauma:

  • During vaginal delivery, overstretching or avulsion of the levator ani from the pubic bone can lead to long-term pelvic floor dysfunction.

• Pelvic floor rehabilitation:

  • Pelvic floor muscle training, including biofeedback and electrical stimulation, targets the levator ani to improve symptoms of prolapse or incontinence.