Topics

Topic

design image
Sacrococcygeal joint

The sacrococcygeal joint is the articulation between the apex of the sacrum and the base of the coccyx. It represents the terminal joint of the vertebral column and is typically a secondary cartilaginous joint (symphysis) that may partially or completely ossify with age.

This joint allows limited flexion and extension of the coccyx and is an important landmark in pelvic anatomy, spinal imaging, obstetrics, and evaluation of coccygeal disorders.

Synonyms

  • Sacrococcygeal symphysis

  • Coccygeal joint

Location

  • Situated at the inferior end of the vertebral column

  • Between the fifth sacral vertebra (S5) and the first coccygeal segment (Co1)

  • Posterior to the pelvic viscera

  • Anterior to the subcutaneous tissues of the natal cleft

  • Inferior to the sacral hiatus

Anatomical components

  • Articular surfaces:

    • Apex of the sacrum

    • Base of the coccyx

  • Intervening disc:

    • Fibrocartilaginous disc similar to an intervertebral disc

  • Ligamentous support:

    • Anterior sacrococcygeal ligament

    • Posterior superficial sacrococcygeal ligament

    • Posterior deep sacrococcygeal ligament

    • Lateral sacrococcygeal ligaments

Relations

Anteriorly:

  • Rectum

  • Presacral fascia

Posteriorly:

  • Skin and subcutaneous tissues of the intergluteal region

Superiorly:

  • Sacral canal and sacral hiatus

Inferiorly:

  • Coccygeal segments

Laterally:

  • Attachments of pelvic floor muscles and ligaments

Developmental anatomy

  • Initially a true cartilaginous joint with an intervening disc

  • Progressive fusion common with advancing age

  • Complete synostosis may occur in older adults

  • Mobility varies between individuals and is often greater in females

Function

  • Limited mobility: Allows slight flexion and extension of the coccyx

  • Load distribution: Transmits forces during sitting

  • Pelvic floor attachment: Provides anchorage for levator ani and coccygeus muscles

  • Obstetric relevance: Posterior movement of the coccyx increases pelvic outlet diameter

X-ray appearance

Lateral sacrococcygeal radiographs:

  • Joint line: Thin radiolucent space between sacrum and coccyx

  • Alignment: Smooth sacrococcygeal curvature

  • Fusion: Absence of visible joint line in synostosis

  • Coccygeal segments: Variable number and angulation

CT appearance (pre-contrast)

Non-contrast CT:

  • Articular margins: Well-defined cortical outlines of sacral apex and coccygeal base

  • Joint space: Thin hypodense cleft if not fused

  • Fusion: Continuous bone across the joint in synostosis

  • Cortical integrity: Preserved cortical tables and trabecular pattern

  • Alignment: Clear depiction of coccygeal angulation and displacement

MRI appearance

T1-weighted images:

  • Bone marrow: High signal in fatty marrow of sacrum and coccyx

  • Joint disc: Low-to-intermediate signal thin band

  • Cortical bone: Low signal

T2-weighted images:

  • Intervening disc: Intermediate to mildly high signal

  • Joint space: Thin hyperintense line if patent

  • Surrounding soft tissues: Intermediate signal

STIR:

  • Bone marrow: Suppressed fat signal

  • Joint region: Intermediate-to-high signal outlining the fibrocartilaginous disc

  • Soft tissues: High signal relative to fat-suppressed background

MRI image

Sacrococcygeal joint mri anatomy Location and Imaging Appearance -img-00000-00000

MRI image

Sacrococcygeal joint mri anatomy Location and Imaging Appearance -img-00000-00000_00001

MRI image

Sacrococcygeal joint mri anatomy Location and Imaging Appearance -img-00000-00000_00002

CT image

Sacrococcygeal joint ct anatomy Location and Imaging Appearance -img-00000-00000

X Ray image

x ray L SpineAP-img-00000-00000 (1)