Sternoclavicular Joint

Introduction

Introduction to the Sternoclavicular Joint

The sternoclavicular (SC) joint is the only true synovial articulation between the upper limb and the axial skeleton. It is a saddle-type joint that connects the sternal end of the clavicle with the manubrium of the sternum and the first costal cartilage. Despite its small size, the SC joint permits a wide range of movement, including elevation, depression, protraction, retraction, and axial rotation of the clavicle, which are essential for full shoulder girdle mobility. Its strong ligamentous support makes it remarkably stable, yet dislocations and degenerative changes can occur and are clinically significant.

This module covers the articular surfaces, intra-articular disc, ligamentous complex, blood and nerve supply, movements, and clinical conditions of the sternoclavicular joint.

Study

1. Articular Surfaces

The sternoclavicular joint is a double synovial (saddle) joint formed by the sternal (medial) end of the clavicle and the clavicular notch of the manubrium sterni, together with a small portion of the first costal cartilage at its superior surface. The articular surface of the clavicle is much larger than the corresponding surface on the manubrium, and the joint surfaces are covered by fibrocartilage rather than hyaline cartilage, which is atypical for a synovial joint. The incongruence of the bony surfaces is compensated by a strong fibrocartilaginous articular disc.

2. Articular Disc

A complete fibrocartilaginous articular disc divides the joint cavity into two separate synovial compartments (medial and lateral). The disc is attached superiorly to the posterosuperior border of the clavicle and inferiorly to the first costal cartilage near its sternal attachment. It acts as a shock absorber and enhances the fit between the articular surfaces. The disc also plays a critical role in the movements of the joint, particularly during clavicular rotation.

3. Ligamentous Support

The sternoclavicular joint is reinforced by four strong ligaments:

Anterior sternoclavicular ligament: A broad band of fibres covering the anterior aspect of the joint, preventing upward displacement of the clavicle.

Posterior sternoclavicular ligament: A similar but weaker band on the posterior aspect, providing additional stability.

Interclavicular ligament: A strong band connecting the superior surfaces of the sternal ends of both clavicles, with attachment to the suprasternal (jugular) notch. It limits excessive depression of the lateral clavicle.

Costoclavicular ligament: The most important stabiliser of the joint, this short, strong, flattened ligament runs from the inferior surface of the sternal end of the clavicle to the superior surface of the first costal cartilage and adjacent first rib. It limits all movements of the joint and acts as a fulcrum for clavicular elevation.

4. Blood Supply

The arterial supply is derived from branches of the internal thoracic (mammary) artery and the suprascapular artery. Venous drainage follows the corresponding veins into the brachiocephalic system.

5. Nerve Supply

The sternoclavicular joint receives its innervation from the medial supraclavicular nerve (C3, C4) and the nerve to the subclavius (C5, C6). This dual supply explains why pain from the joint can be referred to the shoulder or the neck.

6. Movements

The sternoclavicular joint permits movement of the clavicle in three planes: elevation and depression (about 30–40° in each direction), protraction and retraction (about 25–30° each), and axial rotation (approximately 30° during full abduction of the arm). These movements are essential for positioning the glenoid cavity and enabling full range of motion at the shoulder. Because the joint is a saddle joint with two compartments, the movements occur around the costoclavicular ligament as a pivot point.

7. Clinical Significance

Sternoclavicular joint dislocation: Although rare due to the strong ligamentous support, anterior or posterior dislocations can occur following high-energy trauma. Posterior dislocations are a medical emergency because the medial end of the clavicle can compress the trachea, oesophagus, or great vessels.

Osteoarthritis: Degenerative changes in the SC joint are common with age and can cause local pain and swelling, often confused with thoracic outlet syndrome or cardiac pain.

Septic arthritis: The joint may be affected by haematogenous infection, especially in intravenous drug users, presenting with swelling, erythema, and tenderness.

SAPHO syndrome: A condition involving synovitis, acne, pustulosis, hyperostosis, and osteitis that frequently affects the sternoclavicular joint.

Tietze syndrome: An inflammatory condition causing painful swelling of the costochondral, chondrosternal, or sternoclavicular joints, often mimicking cardiac pain.

Summary

Summary of the Sternoclavicular Joint

The sternoclavicular joint is a saddle-type synovial joint connecting the upper limb to the axial skeleton. It possesses a fibrocartilaginous articular disc dividing its cavity, and is stabilised by four ligaments (anterior and posterior sternoclavicular, interclavicular, and costoclavicular). The joint permits elevation, depression, protraction, retraction, and rotation of the clavicle, vital for shoulder girdle function. While highly stable, the joint is susceptible to traumatic dislocation (particularly posterior, which can be life-threatening), osteoarthritis, and inflammatory conditions.