Topics

Topic

design image
Ischiococcygeus muscle

The ischiococcygeus muscle, also known simply as the coccygeus muscle, is a small triangular muscle of the pelvic floor. It lies posterior to the levator ani and contributes to the support of pelvic viscera. The muscle forms part of the pelvic diaphragm, extending from the ischial spine to the coccyx and lower sacrum. Though small, it plays a stabilizing role in the sacroiliac and sacrococcygeal regions.

It is clinically relevant in pelvic floor dysfunction, trauma, obstetric injuries, and as a landmark in pelvic surgery and imaging.

Synonyms

  • Coccygeus muscle

  • Ischiococcygeus of pelvic diaphragm

  • Posterior pelvic floor muscle

Origin, Course, and Insertion

  • Origin: Ischial spine and pelvic surface of the sacrospinous ligament

  • Course: Fibers pass medially and posteriorly, forming a thin triangular sheet posterior to levator ani

  • Insertion: Lateral borders of the coccyx and lower sacrum

Relations

  • Anteriorly: Ischiorectal fossa and pelvic viscera

  • Posteriorly: Sacrospinous ligament and gluteal region

  • Superiorly: Levator ani muscle (iliococcygeus)

  • Inferiorly: Sacrotuberous ligament and gluteus maximus (laterally)

Function

  • Supports and elevates the pelvic floor

  • Assists the levator ani in supporting pelvic viscera

  • Contributes to stabilization of the coccyx and sacroiliac joint

  • Helps flex the coccyx after defecation or childbirth

Clinical Significance

  • May be injured in childbirth or pelvic trauma

  • Weakness contributes to pelvic organ prolapse and perineal descent

  • Can be a source of pelvic or low back pain (coccygodynia)

  • Landmark in surgical approaches to sacrospinous ligament fixation procedures

  • Visualized in pelvic MRI to evaluate pelvic floor disorders

MRI Appearance

T1-weighted images:

  • Muscle shows low-to-intermediate signal intensity

  • Surrounding fat appears bright and clearly outlines the muscle

  • Hemorrhage or fatty infiltration may show bright signal intensity

T2-weighted images:

  • Normal muscle shows low-to-intermediate signal

  • Edema, inflammation, or injury shows bright hyperintensity

  • Fibrosis or scarring appears as persistently dark areas

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low signal intensity

  • Pathology (inflammation, strain, infection) appears with bright hyperintensity

  • Fat is suppressed and appears dark

T1 Fat-Sat Post-Contrast:

  • Normal muscle enhances mildly and uniformly

  • Pathology shows focal, heterogeneous, or rim enhancement depending on etiology

CT Appearance

Non-Contrast CT:

  • Muscle appears as a thin soft tissue density band extending from ischial spine to coccyx

  • Fat planes around it are seen as low-density regions

  • Hematoma may appear as localized hyperdensity

Post-Contrast CT:

  • Normal muscle enhances mildly and evenly

  • Inflammatory or neoplastic involvement shows heterogeneous enhancement

  • Abscess or necrotic lesions show central low density with rim enhancement

MRI image

Ischiococcygeus muscle MRI axial anatomy image-img-00000-00000

MRI image

Ischiococcygeus muscle MRI axial anatomy image-img-00000-00000_00001

CT image

Ischiococcygeus muscle CT axial anatomy image-img-00000-00000

CT image

Ischiococcygeus muscle CT axial anatomy image-img-00000-00000_00001