Coccygeus

1. Overview

The coccygeus muscle, also known as the ischiococcygeus, is a small triangular muscle that forms part of the pelvic diaphragm. It is located posteriorly within the pelvis and works closely with the levator ani muscles to support the pelvic organs. Although relatively minor in size compared to other pelvic muscles, the coccygeus contributes to the structural integrity of the pelvic floor and assists in voluntary and reflexive functions related to posture and defecation.

2. Location

The coccygeus muscle is located in the posterior part of the pelvic floor:

• Origin: Ischial spine of the hip bone.

• Insertion: Lateral borders of the sacrum and coccyx (S5 to the coccygeal vertebrae).

• Position: Lies posterior to the levator ani and anterior to the sacrospinous ligament, with which it blends closely.

It forms the posterior portion of the pelvic diaphragm and bridges the gap between the sacrum and ischial spine.

3. Structure

The coccygeus is a flat, triangular, skeletal muscle with the following structural features:

• Muscle fiber orientation: Directed superomedially from the ischial spine to the sacrum and coccyx.

• Innervation: Branches of the anterior rami of spinal nerves S4 and S5.

• Associated structures: The muscle is tightly associated with the sacrospinous ligament, often indistinguishable from it in dissection.

• Blood supply: Inferior gluteal artery and branches from internal pudendal artery.

4. Function

The coccygeus muscle serves the following functions:

• Supports pelvic viscera: Contributes to the structural integrity of the pelvic floor along with the levator ani.

• Pulls coccyx forward: Assists in returning the coccyx to its normal position after defecation or childbirth.

• Stabilizes the sacroiliac joint: Through its attachments and muscle tone, it supports pelvic alignment during movement.

5. Physiological role(s)

The coccygeus contributes to multiple physiological functions despite its small size:

• Pelvic floor integrity: Acts with levator ani to support pelvic organs and prevent prolapse.

• Continence mechanisms: Provides secondary support to the anal and urogenital sphincters during increased intra-abdominal pressure (e.g., coughing, lifting).

• Defecation and childbirth: Assists in posterior movement of the coccyx to widen the pelvic outlet, then helps restore its position.

• Postural role: Helps maintain upright posture by supporting pelvic tilt and pelvic base alignment.

6. Clinical Significance

Although less frequently discussed than other pelvic muscles, the coccygeus has several clinical considerations:

• Coccygodynia (coccyx pain):

  • Strain or spasm of the coccygeus may contribute to tailbone pain, especially after trauma or prolonged sitting.

• Pelvic floor dysfunction:

  • Weakness or imbalance involving the coccygeus can be part of broader pelvic floor disorders, including prolapse or fecal incontinence.

• Postpartum changes:

  • The coccygeus may become overstretched or damaged during vaginal childbirth, contributing to postpartum pelvic pain.

• Surgical relevance:

  • Understanding its location is important in sacrospinous ligament fixation procedures for pelvic organ prolapse repair.

• Palpation and therapy:

  • Can be accessed through internal pelvic floor therapy techniques to manage chronic pelvic pain or myofascial dysfunction.