Pubococcygeus

The pubococcygeus is a critical component of the levator ani muscle group and forms the central portion of the pelvic diaphragm. It stretches from the pubic bone to the coccyx and plays a vital role in supporting pelvic viscera, maintaining continence, assisting in vaginal and urethral closure, and contributing to the structural integrity of the pelvic floor. It also blends with other surrounding structures, including the perineal body and walls of the vagina or prostate, making it a functional component in both urogenital and anorectal physiology.

Structure

The pubococcygeus is a paired muscle originating from the inner surface of the pubic bone, specifically the posterior surface of the body of the pubis and the anterior part of the tendinous arch of the obturator fascia. The fibers course posteriorly and medially, running alongside the puborectalis but more laterally. They insert into various midline structures, including the perineal body, coccyx, anococcygeal ligament, and walls of the vagina or prostate depending on sex.

Attachments

Location

The pubococcygeus is situated between the puborectalis medially and the iliococcygeus laterally. It lies superior to the perineal membrane and inferior to the pelvic viscera. It forms the most substantial part of the midline levator ani muscle and spans an arc that curves posteriorly from the pubis to the coccyx, encasing structures like the vagina, urethra, and rectum in the process.

Subdivisions and Gender Differences

In clinical and functional anatomy, the pubococcygeus is sometimes described as having specialized subcomponents, especially in females, although these names are not universally used. They include:

• Pubovaginalis: Inserts into the vaginal wall in females, contributing to vaginal tone and support
• Puboprostaticus: In males, fibers may blend with fascia around the prostate and assist in prostatic support
• Puboperinealis: Inserts into the perineal body, reinforcing central pelvic floor support

These components are not always grossly separable but reflect the multiple roles played by the pubococcygeus in pelvic function.

Function

• Pelvic Organ Support: Forms a muscular sling that supports the bladder, rectum, and (in females) uterus and vagina
• Continence Mechanism: Helps maintain urethral and anal sphincter control, particularly during increases in intra-abdominal pressure
• Sexual Function: In females, contributes to vaginal tightness and orgasmic contractions; in males, supports erectile function by maintaining pelvic tone
• Stabilization: Anchors the perineal body and supports the central tendon of the perineum

Innervation

• Nerve to levator ani (S3–S4): Primary motor innervation
• Pudendal nerve (S2–S4): May contribute through its inferior rectal branches

Vascular Supply

• Inferior gluteal artery
• Internal pudendal artery
• Accompanying venous drainage flows to internal iliac veins

Histology

The pubococcygeus consists of skeletal muscle fibers specialized for tonic activity. It demonstrates a mixture of Type I (slow-twitch) and Type II (fast-twitch) fibers, with a predominance of fatigue-resistant fibers that allow it to maintain prolonged contractions required for pelvic organ support and continence. Interspersed collagen fibers contribute to elasticity and resistance.

Role in Imaging and Evaluation

• Visible on pelvic MRI as a key structure surrounding the urethra and rectum
• Evaluated in 3D endovaginal ultrasound for levator avulsion postpartum
• Palpable during digital pelvic exams for tone and contractility testing

Development

Embryologically, the pubococcygeus arises from the myotomes of the sacral somites (S3–S5), developing in conjunction with other pelvic diaphragm muscles. During fetal development, the muscle fibers migrate medially and posteriorly to integrate with connective tissue structures like the perineal body and coccyx. Postnatally, its function develops alongside voluntary continence and sexual maturity.

Clinical Significance

• Pelvic Organ Prolapse: Weakness or avulsion of the pubococcygeus is strongly associated with uterine, vaginal, or rectal prolapse, especially in multiparous women
• Urinary Incontinence: Loss of support to the urethra from damaged pubococcygeus fibers can result in stress incontinence
• Levator Ani Avulsion: Imaging studies frequently identify unilateral or bilateral detachment of the pubococcygeus from the pubic bone after vaginal delivery
• Sexual Dysfunction: Reduced pubococcygeus tone may be associated with decreased sexual satisfaction or weak orgasmic response
• Pelvic Floor Therapy: Kegel exercises target this muscle specifically to restore tone and improve continence
• Surgical Relevance: Often used as an anchor point in pelvic floor reconstructive surgeries, such as posterior colporrhaphy or rectopexy