Sternoclavicular joint

Location: At the root of the neck on each side of the jugular (suprasternal) notch, where the medial end of the clavicle meets the manubrium of the sternum and the first costal cartilage.

Bones taking part

• Clavicle (sternal end)
• Manubrium of sternum
• First rib
• Costal cartilage of the first rib

Articulating surfaces

• The sternal (medial) end of the clavicle
• The clavicular notch on the superolateral angle of the manubrium of the sternum
• The adjoining upper surface of the first costal cartilage
• The surfaces are covered with fibrocartilage, not hyaline cartilage, and they fit poorly: the sternal end of the clavicle is much larger than the notch and stands above it.

Structural

Synovial joint (saddle type), with an articular disc dividing it into two compartments.

Functional

Diarthrosis (freely movable).

Synovial subtype

Saddle (sellar). Because of the articular disc it moves in all directions, so it functions like a ball-and-socket joint even though its surfaces are saddle-shaped.

Axes

Structurally biaxial (saddle); with the disc it permits movement about three axes, including rotation of the clavicle, so it is functionally multiaxial.

Capsule & cavity

A fibrous capsule surrounds the joint and attaches to the margins of the articular surfaces, including the periphery of the articular disc. It is thickened in front and behind by the anterior and posterior sternoclavicular ligaments. Each of the two joint compartments has its own synovial membrane.

• Connects the upper limb to the axial skeleton: it is the only bony link between them.
• Acts as the pivot about which the clavicle, and therefore the shoulder girdle, moves.
• Transmits force from the upper limb, along the clavicle, to the sternum; the disc absorbs part of it.
• Lets the scapula move freely so the arm can be raised above the head.

Stability vs mobility: Very strong for its shallow, poorly fitting bony surfaces. Stability comes from the articular disc, the capsule and the sternoclavicular, interclavicular and costoclavicular ligaments, not from the shape of the bones. It is so strong that a fall on the shoulder usually fractures the clavicle before it dislocates this joint.

• Dislocation of the sternoclavicular joint is uncommon because the joint is so strong; the clavicle usually fractures first.
• Anterior dislocation is more common than posterior. Posterior dislocation is the more dangerous: the medial end of the clavicle can press on the great vessels, trachea or oesophagus behind the manubrium.
• In younger people, an apparent dislocation may actually be a separation through the growth plate at the sternal end of the clavicle, which is one of the last epiphyses to fuse.
• The joint can be affected by arthritis or infection, which present as swelling and pain beside the jugular notch.

• Name it as the only synovial (bony) joint linking the upper limb to the axial skeleton.
• Classify it carefully: saddle type of synovial joint, but functionally like a ball-and-socket joint because of the disc.
• State that it has an articular disc dividing it into two compartments, each with its own synovial membrane.
• Name the costoclavicular ligament as its main stabiliser and say where it attaches.
• Articular surfaces are covered with fibrocartilage, as at the acromioclavicular joint, not with hyaline cartilage.
• Tell it apart from the acromioclavicular joint: the SC joint is at the medial end of the clavicle, has a complete disc, and is saddle type; the AC joint is at the lateral end and is a plane joint.

• Calling it a ball-and-socket joint outright. Structurally it is saddle-shaped; it only behaves like a ball-and-socket joint because of the disc.
• Forgetting the first costal cartilage as part of the articulation.
• Saying the disc is at the AC joint only. The SC joint has a complete disc; the AC joint's disc is often incomplete.
• Thinking the interclavicular ligament is the main stabiliser; the costoclavicular ligament is.
• Thinking shoulder abduction happens here. The arm moves at the glenohumeral joint; the SC joint moves the girdle.