The clavicle is a long bone that extends horizontally from the sternum’s superior portion to the scapula’s acromion (shoulder blade). Together, the clavicle and scapula make up the shoulder (pectoral) girdle.
The clavicle or collarbone has several important functions.
First, anchored by muscles from above, it serves as a strut that extends laterally to support the scapula.
The horizontally positioned clavicle holds the shoulder joint superiorly and laterally from the body trunk, allowing for maximal freedom of movement for the upper limb.
The clavicle also transmits forces acting on the upper limb to the sternum and axial skeleton.
Finally, it protects the underlying nerves and blood vessels as they pass between the body’s trunk and the upper limb.
The clavicle is divided into a rounded medial end, a flattened lateral end, and a central shaft. The medial end curves anteriorly and the lateral end curves posteriorly, which gives the bone an S-shaped appearance. The curves are best seen when the bone is viewed from above or below.
There are some sex differences in the morphology of the clavicle. The clavicle tends to be shorter, thinner, and less curved in women. In men, the clavicle is more massive and longer and has a greater curvature and rougher surfaces where muscles and ligaments attach.
Clavicular Shape and Orientation
Lateral End Shaft Medial End
The clavicle articulates with two bones. Its medial (sternal) end articulates with the manubrium (upper end) of the sternum to form the sternoclavicular joint. This joint is the only bony articulation between the pectoral girdle of the upper limb and the axial skeleton. This joint allows considerable mobility, enabling the clavicle and scapula to move in upward/downward and anterior/posterior directions during shoulder movements. The lateral (acromial) end of the clavicle articulates with the acromion of the scapula to form the acromioclavicular joint.
Joints of the Clavicle
The anterior and posterior sternoclavicular ligaments directly attach the clavicle to the upper end of the sternum at the sternoclavicular joint. Stabilizing the joint is the costoclavicular ligament (costo- = “rib”), which extends from the sternal end of the clavicle to the underlying first rib.
At the acromioclavicular joint, the articulating bones are directly attached by the superior and inferior acromioclavicular ligaments. The acromioclavicular joint transmits forces from the upper limb to the clavicle. The ligaments around this joint are relatively weak. A hard fall onto the elbow or outstretched hand can stretch or tear the acromioclavicular ligaments, resulting in a moderate injury to the joint. However, the primary support for the acromioclavicular joint comes from a strong ligament called the coracoclavicular ligament consisting of an anterior deltoid ligament and a posterior conoid ligament. These ligaments anchor the scapula’s coracoid process to the clavicle’s inferior surface, stabilizing the acromioclavicular joint.
Ligaments of the Clavicle
Inferior Surface Anatomy
Along its inferior surface, the clavicle is roughed and bears several surface features. On the lateral side of the bone is the trapezoid line (or trapezoid ridge, or oblique), which runs forward and lateralward, and affords attachment to the trapezoid ligament. Medial to the trapezoid line is the conoid tubercle. This bump-like elevation is an attachment point for the conoid ligament. A depression called the subclavian groove extends along the clavicle’s inferior shaft. It is an attachment site for the subclavius muscle, which originates on the first rib. The costal tuberosity (or impression for costoclavicular ligament) is on the medial part of the clavicle. This broad roughed surface is the attachment site for the costoclavicular ligament, which connects the clavicle to the first rib.
Inferior Surface of the Clavicle
Labeled and Unlabeled Versions
(1500px X 1000 px)
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Reference: “The Pectoral Girdle“