Sternoclavicular Joint

The sternoclavicular joint is the articulation between the medial end of the clavicle and the manubrium of the sternum, along with a small part of the first costal cartilage. It is the only true joint connecting the upper limb to the axial skeleton, playing a vital role in upper limb mobility and positioning. Despite its small size, it is highly stable and permits significant movement of the shoulder girdle.

Structure

The sternoclavicular joint is a synovial saddle joint functionally acting as a ball-and-socket joint. It contains a fibrocartilaginous articular disc that divides the joint cavity into two separate synovial compartments.

Articulating Surfaces

• Medial end of the clavicle: Broad and somewhat convex, articulates with the manubrium and the first costal cartilage.
• Manubrium of sternum: Concave surface on the superolateral aspect.
• First costal cartilage: Contributes to the inferior portion of the articulation.

Articular Disc

• Fibrocartilaginous structure that completely separates the joint into two cavities.
• Attached superiorly to the clavicle and inferiorly to the first rib and manubrium.
• Acts as a shock absorber and enhances joint stability.

Joint Capsule and Ligaments

• Capsule: Thick and reinforced by surrounding ligaments.
• Anterior and posterior sternoclavicular ligaments: Strengthen the capsule in front and behind.
• Interclavicular ligament: Connects the two clavicles across the superior aspect of the manubrium.
• Costoclavicular ligament: Connects the clavicle to the first rib and costal cartilage; limits elevation of the clavicle.

Location

The sternoclavicular joint is located at the junction of the medial end of the clavicle and the manubrium of the sternum, just lateral to the jugular notch at the superior anterior thoracic wall.

Function

• Mobility: Allows movement of the clavicle in three planes—elevation/depression, protraction/retraction, and axial rotation.
• Stability: Maintains the connection between the upper limb and axial skeleton through strong ligamentous support.
• Shock absorption: The articular disc cushions forces transmitted from the upper limb to the trunk.

Development

The sternoclavicular joint develops during early fetal life. The clavicle begins ossification around the fifth week of gestation, and the joint becomes a functional synovial joint with a well-formed disc by birth. The medial clavicular epiphysis is the last to fuse—typically around age 25.

Clinical Significance

• Sternoclavicular dislocation: Uncommon due to strong ligamentous support; anterior dislocations are more common and usually benign, whereas posterior dislocations can be life-threatening due to proximity to major vessels and trachea.
• Osteoarthritis: Can affect the SC joint, especially in older adults or individuals with repetitive upper limb use.
• Sternoclavicular joint infection (septic arthritis): Rare but serious; may present with swelling, fever, and restricted motion.
• Fractures near the SC joint: May mimic dislocation and require imaging for proper diagnosis.