The sternoclavicular articulation is a synovial double-plane joint composed of two portions separated by an articular disc. The parts entering into its formation are the sternal end of the clavicle, the upper and lateral part of the manubrium sterni (clavicular notch of the manubrium sterni), and the cartilage of the first rib, visible from the outside as the suprasternal notch. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage, which is considerably thicker than that on the latter bone.
The sternoclavicular joint allows movement of the clavicle in three planes, predominantly in the anteroposterior and vertical planes, although some rotation also occurs. Muscles don't directly act on this joint, although almost all actions of the shoulder girdle or the scapula will cause some motion at this articulation.
The unique double-hinged articular disk found at the junction of the clavicular head and manubrium allows for movement between the clavicle and the disk during elevation and depression of the scapula. This disk also allows motion between the sternum (manubrium) and itself during protraction and retraction of the scapula.
During protraction, the concave surface of the medial clavicle moves on the convex sternum, producing an anterior glide of the clavicle, and an anterior rotation of the lateral clavicle. With retraction, the medial clavicle articulates with a flat surface and tilts or swings, causing an anterolateral gapping, and a posterior rotation at the lateral end. These movements are usually associated with abduction (protraction) and adduction (retraction) of the scapula, since the scapula is attached to the distal end of the clavicle.
During elevation, the clavicle rotates upward on the manubrium, and produces and inferior glide to maintain joint contact. The reverse actions happen when the clavicle is depressed. The motions are usually associated with elevation and depression of the scapula.
Ligaments and Capsule
- Anterior sternoclavicular ligament
- Articular capsule
- Articular disk
- Costoclavicular ligament
- Interclavicular ligament
- Posterior sternoclavicular ligament
The sternoclavicular joint capsule is fairly strong but is dependent on the ligaments noted above for the majority of its support.
As noted above, there are no muscles that act directly on the sternoclavicular joint. However, the motions of the sternoclavicular joint closely mimic the reciprical motions of the scapula. In addition, the following muscles have an attachment of the clavicle and therefore may produce movement of the clavicle:
- Pectoralis major (clavicular head)