Articular surfaces and structure
The joint is formed by two bones, so according to the classification, it is considered simple. The following participate in its formation:
- Articular head: articular surface on the sternal end of the clavicle (facies articularis extremitatis sternalis claviculae).
- Articular fossa: clavicular notch on the manubrium of the sternum (incisura clavicularis).
- The cartilage of the 1st rib also participates in the articulation.
The main anatomical feature of the articulation is that the articular surfaces are incongruent. This means they do not match each other in shape and size: the head of the clavicle protrudes significantly, while the fossa on the sternum is too small.
To compensate for this mismatch, an articular disc (discus interarticularis) is located inside the cavity. It divides the cavity into two isolated chambers, making the joint complex. The joint capsule is attached along the margins of the articular surfaces and is quite lax, which further contributes to mobility.
Biomechanics and axes of movement
In shape, the joint is a saddle joint. In classical anatomy, saddle joints are usually biaxial, but articulatio sternoclavicularis is an exception. Due to the presence of the intra-articular disc, which smooths out the surfaces and adds degrees of freedom, the joint functions as multiaxial.
Movements occur around three axes:
- Sagittal axis (main): provides movement of the scapula together with the clavicle upwards (elevation) and downwards (depression).
- Vertical axis: allows the clavicle to be pushed forward and retracted backward.
- Proper longitudinal axis (runs along the long axis of the clavicle): provides rotation of the clavicle around its axis.
Ligamentous apparatus
Despite the lax capsule, the joint is securely reinforced by a powerful ligamentous apparatus. The ligaments limit excessive mobility and stabilize the clavicle.
- Sternoclavicular ligaments (ligamentum sternoclaviculare anterius, posterius, superius et inferius). Located anteriorly, posteriorly, superiorly, and inferiorly, respectively, firmly connecting the bone ends.
- Interclavicular ligament (ligamentum interclaviculare). Stretches between the medial ends of the right and left clavicles, passing directly above the jugular notch of the sternal manubrium.
- Costoclavicular ligament (ligamentum costoclaviculare). A very strong ligament that anchors the sternal end of the clavicle to the cartilage and body of the first rib, limiting upward movement of the clavicle.
Clinical Significance and Trauma
From a biomechanical standpoint, the joint transmits enormous forces generated during shoulder movement to the axial skeleton. Due to high continuous loads, it has a high propensity to develop osteoarthritis, which is frequently associated with chronic anterior subluxations.
Injuries (dislocations and subluxations) most commonly occur anteriorly. Posterior dislocation is extremely rare, but is considered a life-threatening condition: the posteriorly displaced medial part of the clavicle can rupture or compress major blood vessels in the superior mediastinum.
For imaging pathologies, conventional radiography has low diagnostic value due to the superimposition of bone shadows. CT or MRI is used for accurate assessment of signs of arthrosis or dislocation.
Topography and venous bed
The anatomy of the sternoclavicular joint is closely related to the major blood vessels of the neck and thoracic cavity. Directly behind this articulation lies a crucial venous confluence.
The internal jugular vein (v. jugularis interna), which collects blood from the cranial cavity and neck organs, descends and ends in the inferior bulb (bulbus inferior v. jugularis). It is precisely at the level of the articulatio sternoclavicularis that it merges with the subclavian vein (v. subclavia).
As a result of this confluence, the brachiocephalic vein (v. brachiocephalica) is formed. The proximity of these large vessels explains the high danger of any injuries accompanied by displacement of the clavicle into the thoracic cavity.
To easily remember the joint ligaments, focus on the bones: sternoclavicular ligaments surround it on all sides, the interclavicular connects the two clavicles above the sternum, and the costoclavicular extends downward to the first rib.
Class and exam questions
Why does a saddle joint function as a multiaxial one?
Multiaxiality is provided by the articular disc (discus interarticularis). It smooths out the anatomical mismatch (incongruence) of the articular surfaces of the sternum and clavicle, adding extra degrees of freedom for movement.
To which type does this joint belong structurally?
By the number of articulating bones, it is simple (formed only by the clavicle and sternum). However, due to the presence of the disc dividing the cavity into two chambers, it is classified as complex.
What is the danger of dislocation in the sternoclavicular articulation?
The most dangerous is a rare posterior dislocation of the clavicle. With such displacement, the bone can damage major vessels of the superior mediastinum (e.g., the brachiocephalic vein, which forms directly behind the joint).
What else to study on this topic
- Anatomy of the internal jugular vein and classification of its tributaries.
- Dural venous sinuses and intracranial veins.
- Structure of the elbow joint, its muscular and ligamentous apparatus.
- MRI diagnostics of labral tears (SLAP lesion).
- Injury to the coracoclavicular ligament and acromioclavicular articulation.
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