Sternoclavicular Joint: Movements, Anatomy, and Function

What is the movement of the sternoclavicular joint?

The sternoclavicular (SC) joint is a highly mobile, saddle-shaped articulation connecting the clavicle to the sternum, serving as the sole bony attachment of the upper limb to the axial skeleton. Its movements—elevation, depression, protraction, retraction, and rotation—are crucial for enabling the extensive range of motion of the shoulder girdle and the entire upper extremity.

Understanding the Sternoclavicular (SC) Joint

The sternoclavicular (SC) joint is a complex articulation located at the root of the neck, where the medial end of the clavicle meets the manubrium of the sternum and the cartilage of the first rib. Despite being classified as a saddle joint, its functional capabilities allow it to operate more like a ball-and-socket joint, providing three degrees of freedom for movement.

Key Anatomical Features:

• Articulating Surfaces: The sternal end of the clavicle, which is convex superior-inferiorly and concave anterior-posteriorly, articulates with the shallow clavicular notch of the manubrium and the first costal cartilage.
• Articular Disc: An essential fibrocartilaginous disc is interposed between the articulating surfaces. This disc divides the joint into two separate synovial cavities, improving congruence, absorbing shock, and preventing medial displacement of the clavicle.
• Ligamentous Support: The joint is reinforced by several strong ligaments that provide significant stability and limit excessive motion. These include the anterior and posterior sternoclavicular ligaments, the interclavicular ligament, and the robust costoclavicular ligament.

The SC joint's unique position and structure make it indispensable for the coordinated movements of the shoulder complex, allowing the scapula and humerus to achieve their wide range of motion.

Key Movements of the Sternoclavicular Joint

The sternoclavicular joint facilitates a variety of movements that contribute significantly to the overall mobility of the shoulder girdle. These movements occur in different planes and around specific axes:

• Elevation:

  • Description: The clavicle moves superiorly, lifting the shoulder girdle upwards. This movement occurs around an anterior-posterior axis.
  • Range of Motion (ROM): Approximately 45-60 degrees.
  • Muscles Involved: Primarily the upper trapezius, levator scapulae, and indirectly the rhomboids.
  • Functional Significance: Essential for shrugging the shoulders, reaching overhead, and lifting objects.

• Depression:

  • Description: The clavicle moves inferiorly, lowering the shoulder girdle. This movement also occurs around an anterior-posterior axis.
  • Range of Motion (ROM): Approximately 10-15 degrees.
  • Muscles Involved: Lower trapezius, pectoralis minor, and subclavius.
  • Functional Significance: Important for pulling movements, depressing the scapula during activities like crutch walking, or pushing down.

• Protraction (Anterior Movement):

  • Description: The clavicle moves anteriorly (forwards) around a vertical axis. This effectively brings the shoulder forward.
  • Range of Motion (ROM): Approximately 15-30 degrees.
  • Muscles Involved: Serratus anterior and pectoralis minor.
  • Functional Significance: Involved in reaching forward, pushing activities, and rounding the shoulders.

• Retraction (Posterior Movement):

  • Description: The clavicle moves posteriorly (backwards) around a vertical axis, pulling the shoulder blade back.
  • Range of Motion (ROM): Approximately 15-30 degrees.
  • Muscles Involved: Rhomboids (major and minor) and middle trapezius.
  • Functional Significance: Crucial for pulling activities, maintaining good posture, and stabilizing the scapula during overhead movements.

• Rotation (Anterior/Posterior):

  • Description: The clavicle rotates along its longitudinal axis. This is often described as anterior rotation (superior surface of the clavicle rotates anteriorly) and posterior rotation (superior surface rotates posteriorly). Posterior rotation is the more significant and extensive movement.
  • Range of Motion (ROM): Up to 30-45 degrees of posterior rotation.
  • Muscles Involved: Not directly driven by specific muscles of the SC joint; rather, it's a passive movement that occurs due to the tension in the costoclavicular ligament as the scapula rotates during glenohumeral movements (e.g., arm abduction or flexion).
  • Functional Significance: Absolutely critical for achieving full range of motion at the glenohumeral (shoulder) joint, particularly during arm elevation (abduction and flexion) beyond 90 degrees. Without adequate posterior rotation of the clavicle, full overhead reaching is significantly limited.

Anatomical Structures Supporting SC Joint Movement

The integrity and function of the SC joint are heavily reliant on its unique anatomical components:

• Articular Disc: This strong, fibrous disc acts as a shock absorber and helps to improve the fit between the incongruent articular surfaces of the clavicle and sternum. It also contributes to the stability of the joint and guides the complex movements.
• Ligaments:
  • Anterior and Posterior Sternoclavicular Ligaments: These broad bands reinforce the joint capsule anteriorly and posteriorly, preventing excessive anterior or posterior displacement of the clavicle.
  • Interclavicular Ligament: Connecting the medial ends of both clavicles across the jugular notch of the sternum, this ligament limits excessive depression and upward displacement of the clavicle.
  • Costoclavicular Ligament: This extremely strong ligament connects the inferior surface of the medial clavicle to the first rib and its costal cartilage. It is a primary stabilizer of the SC joint, limiting elevation of the clavicle and acting as a crucial fulcrum around which the clavicle rotates during arm movements.

These structures work synergistically to provide stability to the joint while permitting a wide range of motion essential for upper limb function.

The SC Joint's Role in Overall Shoulder Girdle Function

The sternoclavicular joint is the linchpin of the entire shoulder girdle. As the sole bony connection of the upper limb to the axial skeleton, its movements directly influence the positioning and mobility of the scapula, and subsequently, the glenohumeral joint (true shoulder joint).

• Foundation for Scapular Movement: The scapula, which has no direct bony attachment to the trunk, moves in conjunction with the clavicle. As the clavicle elevates, depresses, protracts, or retracts at the SC joint, the scapula follows suit.
• Facilitating Glenohumeral Rhythm: Optimal shoulder function relies on the coordinated movement between the glenohumeral joint and the scapulothoracic articulation (the movement of the scapula on the rib cage), known as scapulohumeral rhythm. SC joint movements are an integral part of this rhythm. For example, during overhead arm abduction or flexion, the posterior rotation of the clavicle at the SC joint allows the scapula to upwardly rotate, properly positioning the glenoid fossa for the humerus and preventing impingement.
• Power Transmission: The SC joint acts as a stable base for the transmission of forces from the upper limb to the trunk and vice versa, which is critical for activities involving pushing, pulling, and throwing.

Dysfunction at the SC joint can therefore significantly impair the entire kinetic chain of the upper limb, leading to altered mechanics, pain, and reduced range of motion at the shoulder.

Clinical Relevance and Injury Considerations

While the sternoclavicular joint is remarkably stable due to its strong ligamentous support, injuries can occur.

• Sprains: Ligamentous sprains are the most common type of injury, often resulting from direct trauma to the shoulder or falls onto an outstretched arm.
• Dislocations: Dislocations of the SC joint are rare, but when they do occur, they are typically anterior (clavicle displaces forward). Posterior dislocations, though even rarer, are more serious due to the proximity of vital structures like the trachea, esophagus, and major blood vessels.
• Osteoarthritis: Like other joints, the SC joint can be affected by degenerative changes, leading to pain and stiffness, particularly in older adults or those with a history of trauma.

Understanding the normal biomechanics of the SC joint is crucial for clinicians in diagnosing and treating injuries, and for fitness professionals in designing effective and safe exercise programs that promote optimal shoulder health and function.

Conclusion

The sternoclavicular joint, though often overlooked in favor of the more visibly mobile glenohumeral joint, is a foundational component of the shoulder girdle. Its unique saddle-like structure and robust ligamentous support allow for a complex array of movements—elevation, depression, protraction, retraction, and crucial rotation—that are indispensable for the vast and intricate range of motion of the human upper limb. A healthy and properly functioning SC joint is paramount for everything from simple daily tasks to high-performance athletic endeavors, truly serving as the gateway for all upper extremity movement.