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Manubriosternal joint

The manubriosternal joint is the articulation between the manubrium and the body of the sternum, forming the prominent sternal angle (Angle of Louis). It is classified as a secondary cartilaginous joint (symphysis) composed of fibrocartilage and hyaline cartilage, allowing limited movement while providing strong structural stability to the anterior thoracic cage.

This joint plays a key role in the mechanics of respiration by acting as a hinge point for rib elevation. It also serves as an important anatomical landmark for locating rib levels, the tracheal bifurcation, and mediastinal structures.

Synonyms

  • Sternal angle

  • Angle of Louis

  • Manubriosternal symphysis

Location and Structure

  • Position: Located at the junction of the manubrium and sternal body, at the level of the 2nd costal cartilage.

  • Joint type: Secondary cartilaginous (symphysis) formed by hyaline cartilage covered with fibrocartilage.

  • Supporting structures:

    • Fibrous capsule (weak)

    • Surrounding periosteum

    • Attachments from interclavicular and radiate sternocostal ligaments

  • Surface morphology:

    • Slight angulation forming a palpable ridge

    • Manubrium and sternal body meet at an oblique plane

Relations

  • Anteriorly: Subcutaneous tissue, skin, pectoral fascia

  • Posteriorly: Upper mediastinum, thymic remnants, left brachiocephalic vein, beginnings of great vessels

  • Superiorly: Manubrium and anatomical landmarks such as jugular notch

  • Inferiorly: Sternal body and attachments of 2nd costal cartilages

  • Laterally: Costal cartilages of the second ribs

Function

  • Provides structural stability to anterior thoracic cage

  • Acts as a hinge point during rib movement in respiration

  • Serves as a palpable surface landmark for rib counting and mediastinal orientation

  • Helps maintain shape and rigidity of sternum during breathing and upper limb movement

Clinical Significance

  • Important landmark for tracheal bifurcation level

  • Guides central venous access and mediastinal procedures

  • Provides reference point for CPR hand placement

  • Can show degenerative changes or bony fusion with age (NOT described in imaging section)

MRI Appearance

T1-weighted images:

  • Bone cortex: Low signal (dark)

  • Bone marrow: Bright due to fatty content in sternum

  • Fibrocartilaginous joint space: Intermediate-to-low signal band between manubrium and sternal body

  • Surrounding muscles and soft tissues: Well-differentiated with intermediate signal

T2-weighted images:

  • Cortex: Low signal

  • Bone marrow: Intermediate-to-bright

  • Fibrocartilage: Low signal line outlining the joint

  • Joint space: May show slightly higher signal than cortex due to cartilage hydration

  • Soft-tissue contrast: Clear depiction of mediastinal fat and thoracic wall structures

STIR:

  • Cortex: Low signal

  • Bone marrow: Intermediate-to-dark in normal appearance

  • Fibrocartilaginous joint: Dark linear band

  • Surrounding soft tissues: Homogeneous signal with fat suppression

T1 Fat-Saturated Post-Contrast:

  • Normal manubriosternal joint:

    • No significant enhancement within fibrocartilaginous joint

    • Mild homogeneous enhancement of surrounding soft tissues and periosteum

  • Bone marrow: Subtle uniform enhancement reflecting vascularity

CT Appearance

Non-Contrast CT:

  • Cortex: High density, clearly defined cortical margins

  • Bone marrow: Lower density relative to cortex with visible trabecular pattern

  • Joint space: Visible as a thin linear, slightly lower-density interface

  • Sternal angle: Easily visualized bony landmark on sagittal and axial images

  • Adjacent structures: Clear depiction of mediastinal fat, costal cartilages, and sternoclavicular region

MRI images

Manubriosternal joint SAG MRI IMAGE