Sternoclavicular Joint: Bony and Ligamentous Attachments, Function, and Clinical Relevance

What are the attachments of the sternoclavicular joint?

The sternoclavicular (SC) joint is a crucial articulation connecting the upper limb to the axial skeleton, primarily attaching the medial end of the clavicle to the manubrium of the sternum and the first costal cartilage, reinforced by a robust network of ligaments.

Understanding the Sternoclavicular (SC) Joint

The sternoclavicular joint is a complex, synovial saddle joint that serves as the only direct bony articulation between the upper limb and the trunk. Despite its small size, it plays a pivotal role in the mobility and stability of the entire shoulder girdle, facilitating a wide range of movements for the arm and hand. Its unique structure allows for significant motion while maintaining remarkable inherent stability, largely due to its strong ligamentous attachments and an intra-articular disc.

Bony Attachments

The primary bony structures that form the sternoclavicular joint are:

• Sternal End of the Clavicle: This is the medial, bulbous end of the clavicle, which articulates with the sternum. Its articular surface is typically larger than the sternal facet, contributing to the joint's incongruence, which is compensated for by the articular disc.
• Manubrium of the Sternum: Specifically, the clavicular notch located on the superior-lateral aspect of the manubrium forms the sternal component of the joint.
• First Costal Cartilage: While not directly articulating with the clavicle to form the joint capsule, the first costal cartilage is intimately associated with the SC joint through the strong costoclavicular ligament, which anchors the clavicle to the first rib, providing significant stability.

Ligamentous Attachments (Key Stabilizers)

The stability of the sternoclavicular joint is predominantly provided by a series of powerful ligaments and an intra-articular disc. These structures work in concert to limit excessive motion and prevent dislocation.

• Articular Disc: This fibrocartilaginous disc is located within the joint capsule, dividing the joint into two separate synovial compartments. It attaches superiorly to the clavicle, inferiorly to the first costal cartilage, and peripherally to the joint capsule. The disc significantly enhances joint congruence, acts as a shock absorber, and helps to distribute forces across the joint. It also serves as a pivot point for clavicular rotation during shoulder movements.
• Anterior Sternoclavicular Ligament: This broad, strong band of fibers covers the anterior aspect of the joint capsule. It originates from the sternal end of the clavicle and inserts onto the anterior surface of the manubrium. Its primary role is to resist anterior displacement of the clavicle and limit excessive retraction.
• Posterior Sternoclavicular Ligament: Similar to its anterior counterpart, this ligament reinforces the posterior aspect of the joint capsule. It runs from the posterior surface of the clavicle to the posterior surface of the manubrium. It is crucial in preventing posterior displacement of the clavicle, which is a less common but more clinically significant type of dislocation due to proximity to vital structures like the trachea and great vessels.
• Interclavicular Ligament: This ligament spans the jugular notch of the manubrium, connecting the superior surfaces of the medial ends of both clavicles. It typically blends with the superior aspect of the joint capsules. Its function is to limit excessive depression of the clavicles and provides superior stability, particularly during downward forces applied to the shoulder.
• Costoclavicular Ligament: Considered the strongest and most important ligament of the sternoclavicular joint, the costoclavicular ligament is located external to the joint capsule. It originates from the inferior surface of the medial clavicle and inserts onto the superior surface of the first rib and its costal cartilage. This ligament is a critical anchor, preventing excessive elevation, protraction, and medial displacement of the clavicle. It also acts as a fulcrum for clavicular rotation.

Functional Significance and Clinical Relevance

The intricate array of bony and ligamentous attachments of the sternoclavicular joint allows for a complex interplay of movements, including elevation, depression, protraction, retraction, and axial rotation of the clavicle. These motions are essential for the full range of motion of the scapula and, consequently, the entire upper limb.

Despite its mobility, the SC joint is remarkably stable due to the strength of its ligaments, particularly the costoclavicular ligament and the articular disc. Dislocations of the SC joint are relatively uncommon, especially posterior dislocations, but when they do occur, they can be serious due to the potential for compromise of underlying neurovascular structures. Understanding these attachments is fundamental for clinicians and fitness professionals in diagnosing injuries, designing rehabilitation programs, and appreciating the biomechanics of shoulder girdle movement.

Conclusion

The sternoclavicular joint, formed by the articulation of the clavicle with the sternum and buttressed by the first rib, is a foundational element of the shoulder girdle. Its stability and function are entirely dependent on the precise arrangement and robust nature of its bony components and, most critically, its surrounding and intra-articular ligaments. These attachments collectively ensure that the upper limb remains securely anchored to the axial skeleton while permitting the extensive range of motion necessary for daily activities and athletic performance.