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Sternocostal synchondrosis of first rib

The sternocostal synchondrosis of the first rib is a primary cartilaginous joint (synchondrosis) where the costal cartilage of the first rib unites directly with the manubrium of the sternum. Unlike the second to seventh sternocostal joints, which are synovial, the first sternocostal joint remains a fibrocartilaginous connection without a joint cavity. It provides rigid stability while still allowing limited elasticity during respiration. This synchondrosis may undergo ossification with age, reducing flexibility.

Synonyms

  • First sternocostal joint

  • First costosternal synchondrosis

  • Manubriocostal synchondrosis

Function

  • Anchors the first rib to the manubrium, contributing to thoracic cage stability

  • Permits minimal elastic movement during respiration

  • Serves as an important landmark in thoracic anatomy for imaging and surgical procedures

  • Provides protection for mediastinal structures (great vessels, pleura) behind it

MRI Appearance

T1-weighted images:

  • Costal cartilage and synchondrosis appear as low to intermediate signal intensity

  • Surrounded by hyperintense mediastinal and subcutaneous fat, which provides contrast

  • Ossification or degeneration may appear as areas of low signal intensity

T2-weighted images:

  • Cartilage appears as intermediate signal intensity 

  • Joint margins appear hypointense, reflecting cortical bone

  • Inflammation or edema at the synchondrosis appears as hyperintense foci

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, highlighting edema, inflammation, or cartilage pathology

  • Sternocostal synchondrosis remains low to intermediate signal; pathology appears bright hyperintense

  • Useful for detecting costochondritis or traumatic injury

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal synchondrosis shows little to no enhancement

  • Pathology (costochondritis, infection, neoplasm) may demonstrate enhancement of cartilage or adjacent soft tissues

CT Appearance

Non-contrast CT:

  • The synchondrosis appears as a continuous cartilaginous junction between the first rib and manubrium

  • Cartilage density is lower than bone, with no joint space

  • Ossification may be visualized as hyperdense foci with age

Contrast-enhanced CT (CECT):

  • Surrounding mediastinal and vascular anatomy enhanced for context

  • Pathology (infection, tumor, or inflammatory changes) may be seen as soft tissue thickening or abnormal enhancement around the synchondrosis

  • CT is particularly useful for evaluating trauma, ossification, or neoplastic involvement of the sternocostal junction

MRI images

Sternocostal synchondrosis of first rib anatomy MRI coronal image -img-00000-00000

CT images

Sternocostal synchondrosis of first rib anatomy CT AXIAL image -img-00000-00000