M01.03.031 Sternoclavicular Joint

The sternoclavicular (SC) joint is a vital articulation connecting the clavicle to the manubrium of the sternum. This saddle-type synovial joint plays a crucial role in linking the upper limb to the trunk. In this article, we will explore its structure, neurovascular supply, movements, and clinical relevance.

1. Anatomical Structure of the Sternoclavicular Joint

Articulating Surfaces

The sternoclavicular joint is formed by the following three structures:

• Sternal end of the clavicle
• Manubrium of the sternum
• First costal cartilage (associated with the first rib)

The articular surfaces are covered with fibrocartilage (in contrast to the hyaline cartilage found in most synovial joints). These surfaces are divided into two compartments by a fibrocartilaginous articular disc.

Fig 1.0: Articulating surfaces of the sternoclavicular joint.

Joint Capsule

The joint capsule extends around the borders of the articular surfaces and is lined internally by a synovial membrane. The synovial membrane secretes synovial fluid to reduce friction between the articulating structures.

Ligaments

The stability of the sternoclavicular joint is largely provided by the following ligaments:

1. Sternoclavicular ligaments (anterior and posterior): Reinforce the joint capsule anteriorly and posteriorly.
2. Interclavicular ligament: Attaches the sternal ends of both clavicles and reinforces the joint capsule superiorly.
3. Costoclavicular ligament: Connects the first rib and costal cartilage to the inferior surface of the clavicle. It is the primary stabilizer, preventing elevation of the pectoral girdle.

Fig 2.0: The major ligaments of the sternoclavicular joint.

2. Movements of the Sternoclavicular Joint

The sternoclavicular joint facilitates several types of movement, allowing for significant mobility of the upper limb:

• Elevation: Shrugging the shoulders or raising the arm above 90°.
• Depression: Drooping the shoulders or extending the arm behind the body.
• Protraction: Moving the shoulder girdle forward.
• Retraction: Moving the shoulder girdle backward.
• Rotation: The clavicle rotates as the scapula moves during arm elevation.

Table: Types of Movements

3. Mobility and Stability of the Sternoclavicular Joint

Mobility Factors:

• Type of joint: Being a saddle joint, it allows movement in two axes.
• Articular disc: Enables smooth sliding and rotation between the clavicle and the manubrium.

Stability Factors:

• Joint capsule: Thick and strong, providing structural support.
• Ligaments: The costoclavicular ligament plays a major role in stabilizing the joint, particularly during movements.

4. Blood Supply and Innervation

Arterial Supply:

• Internal thoracic artery
• Suprascapular artery

Innervation:

• Medial supraclavicular nerve (C3 and C4)
• Nerve to subclavius (C5 and C6)

5. Clinical Relevance

Dislocation of the Sternoclavicular Joint

Although rare, dislocations of the sternoclavicular joint can occur due to significant trauma. The costoclavicular ligament and articular disc play a key role in absorbing and transmitting forces, preventing injury to the joint.

Types of Dislocation:

1. Anterior dislocations (more common) occur due to a blow to the anterior shoulder, rotating the shoulder backward.
2. Posterior dislocations (less common) result from a force driving the shoulder forward or a direct impact to the joint.

In adolescents, the dislocation may involve the epiphyseal growth plate of the clavicle, which has not yet been fully ossified, often accompanied by a fracture.

Fig 3.0: Radiography of a right sternoclavicular joint dislocation.

Points to Remember:

• The sternoclavicular joint is a saddle-type synovial joint linking the upper limb with the trunk.
• It allows movements like elevation, depression, protraction, retraction, and rotation.
• The joint is stabilized by sternoclavicular ligaments, interclavicular ligaments, and costoclavicular ligaments.
• Dislocation of the sternoclavicular joint, though rare, may result in either anterior or posterior displacement, often due to significant force.