Pelvic Floor Muscles

1. Overview

The pelvic floor muscles are a group of skeletal muscles and connective tissues that span the bottom of the pelvis, forming a supportive hammock for pelvic organs including the bladder, urethra, rectum, uterus (in females), and prostate (in males). These muscles play a critical role in urinary continence, micturition control, and pelvic organ support. Proper coordination of pelvic floor muscles is essential for normal urinary function, particularly voluntary control over urination and maintenance of intra-abdominal pressure.

2. Location

The pelvic floor muscles are located at the inferior end of the pelvic cavity, enclosing the pelvic outlet. They form a funnel-shaped muscular sheet that stretches from the pubic symphysis anteriorly to the coccyx posteriorly, and between the ischial tuberosities laterally. Key anatomical regions include:

• Pelvic diaphragm: The deeper muscular layer forming the primary floor of the pelvis.

• Urogenital diaphragm (perineal membrane): Lies below the pelvic diaphragm and contains muscles that specifically support the urethra and external genitalia.

3. Structure

The pelvic floor is composed of several muscles, organized into two layers:

Pelvic Diaphragm (deep layer):

• Levator ani group:

  • Pubococcygeus

  • Iliococcygeus

  • Puborectalis (forms a sling around the anorectal junction)

• Coccygeus (ischiococcygeus): Located posteriorly; assists levator ani in forming the floor.

Urogenital Diaphragm (superficial layer):

• External urethral sphincter (voluntary control of urination)

• Deep transverse perineal muscle

• Compressor urethrae and urethrovaginal sphincter (in females)

The muscles are innervated mainly by the pudendal nerve (S2–S4), providing voluntary motor control.

4. Function

The pelvic floor muscles serve multiple key functions, particularly in relation to the urinary system:

• Support pelvic organs: Maintain the position of the bladder and urethra, preventing descent during increases in abdominal pressure.

• Maintain continence: The levator ani and external urethral sphincter contract to keep the urethra closed during bladder filling.

• Coordinate voiding: During micturition, these muscles must relax in coordination with detrusor muscle contraction to allow urine flow.

5. Physiological Role(s)

The pelvic floor muscles are dynamically involved in urinary physiology:

• Storage phase: Maintain closure of the urethra, resisting increases in intra-abdominal pressure (e.g., coughing, sneezing).

• Voiding phase: Voluntary relaxation allows passage of urine; failure to relax results in retention or obstructive symptoms.

• Intra-abdominal pressure regulation: Assist in stabilizing the trunk during physical activity and straining (Valsalva maneuver).

• Sexual function and childbirth: Interact with genital and rectal structures, especially in females during labor and delivery.

6. Clinical Significance

Stress Urinary Incontinence (SUI)

Occurs when pelvic floor muscles weaken and fail to support the urethra adequately. Common causes:

• Vaginal childbirth

• Menopause (due to estrogen deficiency)

• Pelvic surgery or trauma

Treatment includes pelvic floor exercises (Kegels), biofeedback, and surgical options (e.g., sling procedures).

Overactive Pelvic Floor

Excessively tense muscles can lead to:

• Urinary retention

• Painful urination

• Pelvic pain syndromes

Managed with pelvic floor physical therapy, muscle relaxants, and behavioral training.

Pelvic Organ Prolapse

Loss of support from the pelvic floor can result in bladder descent (**cystocele**), contributing to incomplete emptying, incontinence, and urgency. Common in multiparous women and postmenopausal patients.

Neurogenic Bladder

Disruption of pudendal or sacral innervation (e.g., in spinal cord injury, multiple sclerosis) impairs voluntary control of the pelvic floor, leading to incontinence or retention.

Post-Prostatectomy Incontinence (Male)

Damage to the pelvic floor and external urethral sphincter during prostate surgery may result in stress incontinence. Rehabilitation often includes targeted pelvic floor training.

Diagnostic and Therapeutic Relevance

• Urodynamic testing: Assesses coordination of pelvic floor activity with bladder function.

• Electromyography (EMG): Evaluates pelvic floor muscle integrity.

• Biofeedback therapy: Helps patients learn to strengthen or relax pelvic floor muscles.