Sternoclavicular (SC) Joint: The 7 Ligaments That Support It

What are the 7 ligaments that support the SC joint?

The sternoclavicular (SC) joint, a crucial link between the upper limb and the axial skeleton, is stabilized by a robust complex of ligaments, including the anterior and posterior sternoclavicular ligaments, the interclavicular ligament, the anterior and posterior laminae of the costoclavicular ligament, and the strong ligamentous attachments of the intra-articular disc to both the clavicle and the sternum/first rib.

Understanding the Sternoclavicular (SC) Joint

The sternoclavicular (SC) joint is a synovial saddle joint that connects the medial end of the clavicle to the manubrium of the sternum and the first costal cartilage. Despite its seemingly small size, it is the sole bony articulation between the upper limb and the trunk, making its integrity paramount for shoulder girdle function, arm movement, and even respiration. Its unique design allows for significant mobility in multiple planes (elevation/depression, protraction/retraction, and some axial rotation), while simultaneously requiring immense stability to transmit forces from the upper limb to the axial skeleton. This dual requirement for mobility and stability is expertly managed by a strong fibrous capsule and a powerful array of reinforcing ligaments, augmented by an intra-articular disc.

The Ligaments Supporting the SC Joint

The stability of the SC joint relies heavily on its surrounding ligamentous structures. While some classifications might group these differently, a comprehensive understanding of the key fibrous components contributing to its strength reveals seven distinct elements:

1. Anterior Sternoclavicular Ligament:

   • Location/Attachments: This strong, broad band covers the anterior surface of the joint capsule, extending from the anteromedial aspect of the clavicle obliquely downwards and medially to the anterior surface of the manubrium and the first costal cartilage.
   • Function: It is a primary stabilizer, preventing excessive posterior displacement of the clavicle and resisting superior displacement, particularly during movements like shrugging or overhead lifting.

2. Posterior Sternoclavicular Ligament:

   • Location/Attachments: Found on the posterior aspect of the joint, this ligament runs from the posteromedial aspect of the clavicle to the posterior surface of the manubrium.
   • Function: Less robust than its anterior counterpart, it primarily limits anterior displacement of the clavicle and reinforces the posterior joint capsule.

3. Interclavicular Ligament:

   • Location/Attachments: This ligament spans the jugular (suprasternal) notch, connecting the superior borders of the medial ends of both clavicles. Some fibers blend with the superior aspect of the sternal manubrium.
   • Function: It plays a crucial role in preventing excessive upward displacement (elevation) of the clavicle, particularly during shoulder depression. It also helps to distribute forces evenly across both clavicles.

4. Costoclavicular Ligament (Anterior Lamina):

   • Location/Attachments: An extremely strong, extrinsic ligament located inferior and slightly posterior to the SC joint. It consists of two laminae. The anterior lamina originates from the superomedial surface of the first costal cartilage and inserts onto the inferior surface of the medial clavicle.
   • Function: This lamina primarily resists superior and medial displacement of the clavicle relative to the sternum, acting as a crucial checkrein against upward and inward movement.

5. Costoclavicular Ligament (Posterior Lamina):

   • Location/Attachments: Also part of the costoclavicular ligament, the posterior lamina lies deep to the anterior lamina, separated by a small bursa. It originates from the first rib and inserts onto the clavicle, with its fibers running in an opposite direction to the anterior lamina.
   • Function: The posterior lamina primarily limits lateral and inferior displacement of the clavicle, complementing the anterior lamina's role in providing robust overall stability to the joint.

6. Articular Disc Ligamentous Attachment (to Clavicle):

   • Location/Attachments: The sternoclavicular joint contains a strong intra-articular disc of fibrocartilage. This disc is firmly attached superiorly and posteriorly to the medial end of the clavicle, essentially acting as a strong ligamentous anchor between the disc and the clavicle.
   • Function: This attachment provides significant stability by binding the clavicle to the disc, which in turn is anchored to the sternum and first rib, preventing excessive movement of the clavicle relative to the disc.

7. Articular Disc Ligamentous Attachment (to Sternum/First Rib):

   • Location/Attachments: The intra-articular disc is also firmly attached inferiorly and anteriorly to the superior border of the manubrium and the first costal cartilage. These strong fibrous connections are ligamentous in nature.
   • Function: These attachments integrate the disc with the sternum and first rib, allowing the disc to act as a pivot point and shock absorber, crucially enhancing stability by preventing superior dislocation of the clavicle and distributing forces across the joint.

The Critical Role of SC Joint Stability

The intricate network of these seven ligamentous components ensures the remarkable stability of the sternoclavicular joint. Given its pivotal role as the only bony connection of the upper limb to the axial skeleton, any compromise to its integrity, such as a ligamentous tear or rupture, can severely impair upper limb function, leading to pain, instability, and limitations in range of motion. Understanding the specific contributions of each ligament is fundamental for clinicians, therapists, and fitness professionals in diagnosing injuries, developing rehabilitation protocols, and designing effective training strategies to maintain shoulder girdle health and performance.

Conclusion

The sternoclavicular joint, despite its small size, is a cornerstone of shoulder girdle mechanics, owing its robust stability to a sophisticated arrangement of ligaments. The anterior and posterior sternoclavicular ligaments, the interclavicular ligament, the anterior and posterior laminae of the costoclavicular ligament, and the strong ligamentous attachments of the intra-articular disc to both the clavicle and the sternum/first rib collectively form a formidable protective complex. Each of these seven components plays a distinct yet synergistic role in limiting excessive motion, absorbing forces, and maintaining the crucial connection that allows for the vast and dynamic movements of the human arm.