Learning Objectives

By the end of this lesson, you should be able to:

1. Describe the anatomical structure of the sternoclavicular joint.
2. Identify the ligaments that stabilize the joint and explain their functions.
3. List the movements permitted at the sternoclavicular joint.
4. Explain how the joint balances mobility with stability.
5. Describe the blood supply and innervation of the joint.
6. Recognize the clinical features of sternoclavicular joint dislocation.

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The sternoclavicular (SC) joint is the only true bony connection between the upper limb and the axial skeleton. It is formed by the articulation of the sternal end of the clavicle with the manubrium of the sternum and the first costal cartilage.

It is classified as a saddle-type synovial joint, allowing a wide range of movements while remaining strong enough to transmit forces from the upper limb to the trunk.

In this section, we will examine the anatomy, stability, movements, blood supply, innervation, and clinical relevance of the sternoclavicular joint.

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Anatomical Structure

Articulating Surfaces

The sternoclavicular joint is formed by three structures:

• Sternal end of the clavicle
• Manubrium of the sternum
• First costal cartilage

Unlike most synovial joints, the articular surfaces are covered with fibrocartilage rather than hyaline cartilage.

The joint cavity is divided into two compartments by a fibrocartilaginous articular disc, which improves joint congruence and absorbs shock.

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Joint Capsule

The fibrous joint capsule attaches to the margins of the articular surfaces and encloses the joint.
It is lined internally by a synovial membrane, which secretes synovial fluid to reduce friction and nourish the cartilage.

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Ligaments

The SC joint is strongly stabilized by four major ligaments:

1. Anterior and posterior sternoclavicular ligaments
   1. Reinforce the joint capsule on the front and back.
2. Interclavicular ligament
   1. Spans between the medial ends of both clavicles and strengthens the superior capsule.
3. Costoclavicular ligament
   1. Connects the clavicle to the first rib and the costal cartilage.
   2. Primary stabilizing structure of the joint, resisting elevation of the shoulder girdle.

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Movements

The sternoclavicular joint allows a wide range of shoulder girdle movements:

• Elevation – shrugging the shoulders, raising the arm above 90°
• Depression – lowering the shoulders
• Protraction – moving the shoulders anteriorly
• Retraction – pulling the shoulders posteriorly
• Rotation – passive rotation of the clavicle during overhead arm movement

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Mobility and Stability

The SC joint must be both mobile and stable.

Factors Promoting Mobility

• The saddle joint structure allows movement in two axes.
• Articular disc permits rotation and gliding in a third axis.

Factors Promoting Stability

• Strong joint capsule
• Powerful ligaments, especially the costoclavicular ligament, which transfers forces from the upper limb to the sternum.

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Blood Supply

The joint is supplied by branches of:

• Internal thoracic artery
• Suprascapular artery

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Innervation

The sternoclavicular joint is innervated by:

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

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Clinical Relevance

Dislocation of the Sternoclavicular Joint

SC joint dislocation is rare and requires significant force, as the costoclavicular ligament and articular disc absorb most stresses.

There are two types:

• Anterior dislocation (more common):
  Caused by a blow to the anterior shoulder that forces the shoulder backward.
• Posterior dislocation (less common, more dangerous):
  Caused by a force driving the shoulder forward or direct trauma to the joint.
  It may compress vital structures such as the trachea or major vessels.

In adolescents, the medial clavicular growth plate may fracture instead of a true joint dislocation.

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Activity