Pelvic diaphragm

The pelvic diaphragm is a funnel-shaped muscular and fascial structure that forms the floor of the true pelvis. It supports the pelvic viscera, maintains continence, and separates the pelvic cavity from the perineum. Composed mainly of the levator ani and coccygeus muscles, along with their associated fasciae, the pelvic diaphragm plays a crucial role in posture, organ support, and voluntary control over defecation and urination. In females, it also contributes to vaginal support and childbirth mechanics.

Structure

The pelvic diaphragm is formed by paired muscles and layers of connective tissue. It spans the area between the pubis anteriorly, ischial spines laterally, and the coccyx posteriorly.

Muscles of the Pelvic Diaphragm

Levator Ani Subdivisions

• Puborectalis: Forms a U-shaped sling around the anorectal junction; essential for maintaining fecal continence
• Pubococcygeus: Runs from the pubis to the coccyx; supports pelvic organs and contributes to vaginal and anal sphincter control
• Iliococcygeus: Originates from the tendinous arch of the obturator fascia; inserts into the coccyx and anococcygeal ligament

Location

The pelvic diaphragm is located at the base of the lesser (true) pelvis. It stretches like a hammock from the pubic bones anteriorly to the coccyx posteriorly, and from one ischial spine to the other. Inferior to it lies the perineum, and superiorly is the pelvic cavity. Openings in the diaphragm allow for passage of the urethra, rectum, and (in females) the vagina.

Function

• Support of Pelvic Viscera: Prevents descent of the bladder, rectum, uterus, and other pelvic organs
• Continence: Assists in voluntary control of defecation and urination by supporting the anorectal and urogenital junctions
• Pressure Regulation: Works with abdominal muscles to regulate intra-abdominal pressure during coughing, sneezing, lifting, and childbirth
• Postural Support: Provides structural support during standing and sitting by stabilizing the pelvic outlet

Openings in the Pelvic Diaphragm

Innervation

• Nerve supply: Primarily from the nerve to levator ani (S3–S4) and branches of the pudendal nerve (S2–S4)

Clinical Significance

• Pelvic Organ Prolapse: Weakening or damage to the pelvic diaphragm can lead to descent of the uterus, bladder (cystocele), or rectum (rectocele)
• Fecal and Urinary Incontinence: Loss of support from puborectalis or associated sphincters can impair continence mechanisms
• Childbirth-Related Injury: Vaginal delivery can stretch or tear pelvic diaphragm muscles, especially pubococcygeus, leading to long-term pelvic floor dysfunction
• Pelvic Floor Rehabilitation: Physical therapy, including Kegel exercises, targets pelvic diaphragm strength to manage prolapse and incontinence
• Herniation (Perineal Hernia): Rare but possible defect through the pelvic diaphragm resulting in protrusion of abdominal contents into the perineum