Pelvic Muscles

The pelvic muscles are a group of skeletal muscles that form the muscular walls and floor of the pelvis. They are essential in supporting pelvic organs, maintaining continence, aiding childbirth, and contributing to posture and core stability. These muscles are generally divided into two major categories: the pelvic wall muscles and the pelvic floor muscles. The pelvic diaphragm, forming the deepest layer of the pelvic floor, is the most critical muscular structure in this region and is composed of the levator ani group and the coccygeus muscle. Understanding the anatomy and function of pelvic muscles is foundational in clinical fields such as urology, gynecology, colorectal surgery, and physical therapy.

Structural Organization

The muscular anatomy of the pelvis is organized in layered fashion:

• Pelvic wall muscles: including piriformis and obturator internus
• Pelvic diaphragm (floor): including the levator ani and coccygeus muscles
• Perineal muscles (superficial and deep layers): involved in genital and sphincter control, not typically part of the pelvic diaphragm

This article focuses on the core components of the pelvic diaphragm, the deepest and most functionally critical layer of pelvic musculature.

Pelvic Diaphragm Overview

The pelvic diaphragm forms a muscular funnel that stretches from the pubic bones in the front to the coccyx in the back and from one lateral pelvic wall to the other. It separates the pelvic cavity from the perineum and provides dynamic support to pelvic viscera. It consists of the paired levator ani muscles (puborectalis, pubococcygeus, and iliococcygeus) and the coccygeus muscle.

Levator Ani Muscle Group

The levator ani is the largest component of the pelvic floor. It originates from a linear thickening of fascia on the internal surface of the obturator internus called the tendinous arch. The muscle fibers sweep inferiorly and medially to converge around the midline, surrounding the openings of the urethra, vagina (in females), and anal canal. Each subdivision plays a distinct functional and anatomical role.

Puborectalis

This U-shaped muscle forms a sling around the anorectal junction. It originates from the pubic bodies and inserts into the fibers of the opposite side behind the anorectal junction. It plays a key role in maintaining the anorectal angle and is vital for fecal continence. Contraction pulls the rectum forward, enhancing the angle and preventing involuntary defecation.

Pubococcygeus

Located just lateral to puborectalis, it extends from the pubic bone and inserts into the anococcygeal ligament and coccyx. It supports the urethra, vagina, prostate, and rectum. In females, some fibers may insert into the perineal body, vaginal wall, or even the urethra. Damage to this muscle during childbirth is a key contributor to pelvic organ prolapse.

Iliococcygeus

Arises from the tendinous arch and ischial spine, inserting into the coccyx and anococcygeal ligament. Although thinner and less muscular than the other two, it provides essential lift to the pelvic floor and helps maintain organ positioning. It is often the most fascial of the three parts and may appear aponeurotic in dissection.

Coccygeus (Ischiococcygeus)

The coccygeus muscle lies posterior to the levator ani. It extends from the ischial spine to the lateral margins of the sacrum and coccyx. Though smaller and less active than the levator ani, it plays a structural role in forming the posterior wall of the pelvic diaphragm. It helps stabilize the sacroiliac joint and assists in flexion of the coccyx.

Origin and Insertion Summary

Function

• Pelvic Organ Support: All muscles maintain the position of pelvic viscera including the bladder, uterus, rectum, and prostate
• Continence: Puborectalis is vital in maintaining fecal continence; levator ani as a whole helps support the urethral and anal sphincters
• Pressure Resistance: The pelvic diaphragm resists intra-abdominal pressure during coughing, sneezing, vomiting, and lifting
• Functional Openings: Openings in the diaphragm allow for passage of the rectum, urethra, and (in females) the vagina without compromising support

Innervation

• Levator Ani: Nerve to levator ani (S3–S4), inferior rectal nerve (branch of pudendal, S2–S4)
• Coccygeus: Ventral rami of S4–S5

Development

The pelvic floor muscles develop from the mesoderm of the somites, particularly the hypaxial portion. These muscles migrate into the pelvic region during early fetal life. The innervation pattern reflects their embryological origin from the sacral myotomes. The levator ani and coccygeus begin to take shape as early as the 9th week of gestation and are functionally developed by birth.

Clinical Significance

• Pelvic Floor Disorders: Weakness or trauma to these muscles may result in pelvic organ prolapse, urinary or fecal incontinence, or chronic pelvic pain
• Childbirth Trauma: The pubococcygeus and puborectalis are often injured during vaginal delivery, especially in prolonged labor or instrumental births
• Levator Ani Avulsion: Detachment of the levator ani from the pubic bone, detectable by imaging, is a known risk factor for prolapse
• Pelvic Pain Syndromes: Overactivity or spasm of these muscles may lead to levator ani syndrome or coccygodynia
• Pelvic Floor Therapy: Rehabilitation using biofeedback and Kegel exercises focuses on strengthening these muscles to restore continence and support
• Pelvic Surgeries: Knowledge of the pelvic diaphragm is essential for procedures like hysterectomy, prostatectomy, rectopexy, and sacrospinous fixation