The clavicle, also colloquially known as the collarbone, is the only bone connecting the pectoral girdle to the axial skeleton and is the only long bone that lies horizontally in the human skeleton.

The clavicle is roughly "S-shaped" with a flattened, concave, lateral one-third and a thickened, convex, medial two-thirds. The shaft connects the sternal (medial) end and the acromial (lateral) end. On the inferior surface of the lateral third is the conoid tubercle for the attachment of the conoid ligament and lateral to this is the trapezoid line for attachment of the trapezoid ligament, both constituting the coracoclavicular ligament. On the inferior surface of the medial clavicle is the costal tuberosity and subclavian groove, which form the attachment sites for costoclavicular ligament and subclavius muscle, respectively.

The female clavicle is shorter, thinner, less curved and smoother than the male clavicle.

Articulations

The clavicle articulates with the acromion at the acromioclavicular joint laterally and the sternum at the sternoclavicular joint medially.

Attachments

muscles ⁵
- pectoralis major, sternocleidomastoid (clavicular head), deltoid, trapezius, subclavius, sternohyoid
ligamentous ⁵
- acromioclavicular ligament, coracoclavicular ligament, sternoclavicular ligament, costoclavicular ligament, interclavicular ligament

Arterial supply

nutrient branch from the suprascapular artery
clavicular branch of the thoracoacromial artery from the second part of the axillary artery

Development

Ossification

It is the first bone to start ossification at around 5th-6th weeks of gestation. It is also the last ossification center to fuse, around 22-25 years of age. The lateral end has intramembranous ossification. See main article: ossification centers of the pectoral girdle.

Variant anatomy

forked clavicle
supraclavicular foramen: the clavicle may be pierced by a branch of supraclavicular nerve
coracoclavicular joint
hypertrophic conoid tubercles
at the attachment of the costoclavicular (rhomboid) ligament, there may be a tuberosity or depression (rhomboid fossa) of variable size that may mimic disease; a rhomboid fossa is more common in younger adults and males ⁴

Radiographic features

Plain radiograph

On a chest x-ray image, the clavicles are superimposed over the apex of both the lungs and obscure the subtle lesions. An apical or lordotic view may then provide greater detail of the lung apices.

Chest x-rays are correctly aligned if the medial ends of clavicles are equidistant from the spinous process of vertebrae at the T4/5 level.