The clavicle is a comparatively thin bone of the shoulder girdle that is extremely susceptible to fracture due to its exposed position directly under the skin. Clavicle fractures represent the most common bone fractures, accounting for 10 to 15 percent of all fractures.
What is the clavicle?
The clavicle is the name given to a slightly S-shaped curved bone that is bilateral and belongs to the shoulder girdle along with the two scapulae (shoulder blades). The clavicle articulately connects the sternum (breastbone) to the acromion (shoulder roof, shoulder level), a component of the scapula. Together with the sternum, the clavicle forms the sternoclavicular joint (clavicle-thoracic joint) medially, while with the acromion it forms the acromioclavicular joint (acromioclavicular joint) laterally. Because the clavicle is palpably located under the skin, the bone is often affected by fractures.
Anatomy and structure
The human clavicle is a bone approximately 12 to 15 cm long that is curved or bent in an S-shape. The clavicle is divided into three sections. The Extremitas sternalis is the end section facing the sternum, which has a round articular surface (Facies articularis sternalis) and is counted as the sternoclavicular joint. The end section facing the acromion is called the extremitas acromialis and, together with the acromion, forms the acromioclavicular joint. The articular surface of the extremitas acromialis, called the facies articularis acromialis, has a saddle-shaped flattening. The middle section between these two end sections is called the corpus claviculae and can be divided into a lateral third and two medial thirds. In the lateral third, the fibers of the deltoid muscle radiate anteriorly and those of the trapezius muscle posteriorly. Inferiorly, the ligamentum conoideum, which belongs to the acromioclavicular joint, attaches to the tuberculum conoideum (bony prominence), and the ligamentum trapezoideum attaches to the linea trapezoidea (bony ledge). The two medial thirds of the clavicle have three margins, margo anterior, margo posterior, and margo superior, and three surfaces, facies anterior, facies posterior, and facies inferior.
Functions and tasks
The clavicle is connected medially to the sternum via the sternoclavicular joint and laterally to the scapula via the acromioclavicular joint. Accordingly, the clavicle plays a significant role in the mobility and stability of the shoulder joint. In particular, the lateral elevation (lifting movement) of the arm above the horizontal requires entrainment of both of the aforementioned joints. Although the sternoclavicular joint is located comparatively far from the glenohumeral joint, it participates decisively in shoulder joint movement. The clavicle also functions as an attachment point for various muscles such as the sternocleidomastoid (toward the sternum) and deltoid (toward the acromion) muscles, as well as for various ligaments (including the coracoclavicular ligament and the conoideum ligament). For example, the ligamentum coracoclaviculare stabilizes the acromioclavicular joint and prevents the outer end of the clavicle from sliding away on its high side. The costoclavicular ligament, located at the inferior facies of the two medial thirds, also stabilizes the sternoclavicular joint and fixes the clavicle to the thorax. The deltoid muscle, which attaches to the lateral third of the clavicle, participates in abduction (splaying), anteversion (ventral movement), and retroversion (dorsal flexion) of the arm, among other functions. The trapezius muscle, which attaches to the same third of the clavicle, participates in the lifting movements of the arms and stabilizes the shoulder during heavier stresses such as carrying heavy loads.
Diseases, complaints and disorders
The entire course of the clavicle can be felt just under the skin and, accordingly, is extremely exposed and prone to fracture. Clavicle fractures represent the most common disorder of the clavicle, accounting for 10 to 15 percent of the total number of all bone fractures, with the outermost third affected in the majority of cases. Often, direct force resulting from a bicycle fall, horseback riding accident or other trauma during athletic activities leads to a clavicle fracture. In rare cases, a fall on the outstretched arm may indirectly result in a fracture of the clavicle.A dislocation of the acromioclavicular joint (ACG dislocation) is also a common injury of the clavicle. In this case, an accidental rupture (tearing) in the stabilizing ligamentous and capsular apparatus of the acromioclavicular joint leads to a lifting of the outer end of the clavicle via muscle traction. A palpable step forms subcutaneously between the clavicle end piece and the acromion. Applying pressure to this step can cause the piano key phenomenon characteristic of ligament ruptures. Dislocation of the sternoclavicular joint, on the other hand, occurs rather rarely and can usually be treated conservatively. Age-related degeneration of the acromioclavicular joint can cause arthritic changes with spur formation. Spurs restrict shoulder joint mobility and not infrequently lead to shoulder tightness or impingement syndrome.
