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Coccyx

The coccyx, commonly known as the tailbone, is the terminal portion of the vertebral column. It typically consists of 3–5 fused coccygeal vertebrae, most often four, forming a small triangular bone that articulates superiorly with the sacrum at the sacrococcygeal joint.

Anteriorly, the coccyx provides attachment to the anococcygeal ligament, levator ani, and coccygeus muscles, contributing to pelvic floor support. Posteriorly, it provides insertion to the gluteus maximus muscle. Laterally, it gives attachment to the sacrospinous and sacrotuberous ligaments.

The coccyx plays a crucial biomechanical role in weight-bearing when sitting, especially when leaning backward. It also serves as an anchor for pelvic floor muscles and ligaments. Clinically, the coccyx is important in coccydynia (tailbone pain), fractures, dislocations, and rarely coccygeal tumors.

Synonyms

  • Tailbone

  • Coccygeal bone

  • Terminal vertebral segment

Function

  • Provides attachment for pelvic floor muscles and ligaments, maintaining pelvic organ support

  • Contributes to sitting balance and weight transfer when leaning backward

  • Functions as a vestigial structure, representing the remnant of a tail in humans

Nerve Supply

  • Coccygeal nerve (Co1)

  • Contributions from the fourth and fifth sacral nerves via the coccygeal plexus

Arterial Supply

  • Median sacral artery (from abdominal aorta)

  • Lateral sacral arteries (from internal iliac artery)

Venous Drainage

  • Median sacral vein → left common iliac vein

  • Lateral sacral veins → internal iliac vein

MRI Appearance

T1-weighted images:

  • Bone marrow of coccyx shows intermediate signal intensity

  • Cortical bone appears as a low-signal rim

  • Useful for identifying fractures, degenerative changes, or marrow lesions

T2-weighted images:

  • Cortical bone remains low signal

  • Bone marrow appears as intermediate signal; edema, cysts, or tumor appear hyperintense

  • Useful in evaluating sacrococcygeal joint changes

STIR:

  • Suppresses fat, highlighting marrow edema, fractures, or inflammation as hyperintense regions

  • Highly sensitive for coccydynia and occult fractures

T1 Fat-Saturated (Pre-contrast):

  • Coccyx marrow shows intermediate signal against suppressed fat background

  • Improves contrast for lesion detection

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal coccyx shows mild homogeneous enhancement of marrow

  • Pathology such as infection, inflammation, or tumors shows abnormal, heterogeneous enhancement

MRI Non-Contrast 3D Imaging:

  • Provides multiplanar reconstructions of coccyx alignment, curvature, and morphology

  • Useful for pre-surgical planning and trauma assessment

CT Appearance

CT Pre-Contrast:

  • Coccyx appears as a dense triangular bony structure at the base of the spine

  • Excellent for detecting fractures, dislocations, osteophytes, or anatomic variants

CT Post-Contrast:

  • Enhances surrounding soft tissue and vasculature

  • Useful in evaluating infection, masses, or coccygeal tumors

  • 3D reconstructions help in orthopedic and neurosurgical planning

MRI image

coccyx MRI axial anatomy image -img-00000-00000

MRI image

coccyx MRI coronal anatomy image -img-00000-00000

MRI image

coccyx MRI sag anatomy image -img-00000-00000

CT image

coccyx axil ct image

CT image

coccyx CT sagittal anatomy image -img-00000-00000

CT VRT 3D image

coccyx CT VRT 3D image