Cartilaginous joints of sternum

The cartilaginous joints of the sternum (or Sternal synchondroses) include the manubriosternal joint and the xiphisternal joint.

• The manubriosternal joint is first a synchondrosis (bones are joined by hyaline cartilage) and is termed manubriosternal synchondrosis), and later in life is classified as a symphysis (bones are joined by fibrocartilage). Histologically, it contains both fibroblasts and chondrocytes, and with aging, the joint shows reduced thickness, decreased hydration, and degenerative changes such as hyalinization and focal lesions. This joint rarely undergoes complete ossification, maintaining some degree of mobility throughout life.

• The xiphisternal joint is initially a synchondrosis, composed of hyaline cartilage connecting the sternal body to the xiphoid process. This joint typically ossifies and fuses in middle to late adulthood, resulting in synostosis. Both joints are aligned along the midline of the anterior thoracic wall and are important for the flexibility and integrity of the thoracic cage.

The costal cartilages of ribs 1–7 articulate with the sternum via synchondroses (first rib) and synovial joints (ribs 2–7), but only the manubriosternal and xiphisternal joints are true cartilaginous joints of the sternum itself.