Shoulder Center
The (SC) Sternoclavicular Joint
The Sternoclavicular Joint: Anatomy and Function
The sternoclavicular joint (SCG or SC joint) is a small but essential joint in the human body. It connects the shoulder girdle to the torso and plays a central role in the mobility and stability of the upper musculoskeletal system.
Anatomy of the Sternoclavicular Joint
The SCJ is the only true joint between the shoulder girdle and the axial skeleton. It is a synovial joint surrounded by a joint capsule and stabilized by strong ligaments.
1. Articular surfaces and structure
The SCG is formed by:
01
Medial end of the clavicle (collarbone)
The articular surface at the medial end of the clavicle is larger than that of the opposing structure. It has a saddle-shaped structure.
02
Manubrium sterni (Breastbone)
The upper part of the sternum, together with the first costal cartilage, forms the articular contact surface.
03
First Costal Cartilage
The superior surface of the first costal cartilage forms part of the articulation.
The joint surfaces are covered with a layer of hyaline cartilage. The joint space is divided by an articular disc, which acts as a shock absorber and increases stability.
2. Ligaments of the SCJ
The stability of the SCJ is ensured by several strong ligaments:
01
Anterior and Posterior Sternoclavicular Ligaments
These ligaments run between the medial end of the clavicle and the sternum and stabilize the joint in an anterior-posterior direction.
02
Interclavicular Ligament
Connects the medial ends of the clavicles across the sternum and prevents excessive depression of the shoulder girdle.
03
Costoclavicular Ligament
Attaches the underside of the clavicle to the first costal cartilage and is the most important stabilizing ligament.
3. Joint Capsule
The joint capsule is a dense, fibrous structure that completely surrounds the joint. It is attached to the edges of the articular surfaces and contributes to stability.
4. Blood and nerve supply
01
Blood Supply
The arteries supplying the SCG originate primarily from the internal thoracic artery and the suprascapular artery.
02
Nerve Supply
The joint is innervated by branches of the supraclavicular and subclavius nerves.
Function of the Sternoclavicular Joint
The SCJ is a central component of the shoulder girdle and enables a smooth connection between the upper extremity and the trunk. It has both static and dynamic functions.
1. Movements in the SCJ
The joint allows movement in three degrees of freedom:
01
Elevation and Depression
When raising the shoulders (e.g., hunching the shoulders), the clavicle moves upward (elevation) or downward (depression). This occurs in relation to the first costal cartilage.
02
Protraction and Retraction
Protraction describes the forward movement of the clavicle (e.g., when hugging), while retraction represents a backward movement.
03
Rotation
During movements such as raising the arm, the clavicle rotates around its own axis. This rotation is crucial for full mobility of the shoulder girdle.
2. Stabilization of the shoulder girdle
The SCG is the only bony connection between the shoulder girdle and the torso. It contributes significantly to the stability of the shoulder girdle, especially during movements that require force transfer from the arm to the torso.
3. Force Transmission
The SCG transmits forces from the arm and shoulder to the rib cage and vice versa. This is essential for activities such as lifting, pushing, or pulling.
4. Functional significance of the articular disc
The articular disc in the SCJ has several important functions:
01
It distributes the load evenly across the joint surfaces.
02
It prevents direct friction between the bones and protects against wear.
03
It allows greater freedom of movement and improves joint stability.
Clinical Relevance
Although small, the SCG has great functional significance. Diseases or injuries of the SCG can impair the mobility and stability of the entire shoulder girdle. The most common clinical problems include:
- Dislocations (anterior and posterior)
- Osteoarthritis, common in elderly patients
- Inflammation, e.g., in rheumatoid arthritis
- Fractures of the medial clavicle or the first costal cartilage