Clavicle

The clavicle, also known as the collarbone, is an elongated, thin S-shaped bone that acts like a strut amongst the shoulder blade as well as the sternum (breastbone). Two clavicles have been observed, such that one of these lies on the left and the other on the right. The clavicle seems to be the body's only horizontally oriented long bone.

The shoulder girdle is made up of it and the shoulder blade. It's just like a touchable bone, and in individuals with less fat in this area, the position of the bone is obvious because it produces a protrusion in the skin. Since the bone rotates around its axis like a key whenever the shoulder is seized, it originally comes from the Latin clavicula ("little key").

The much more frequently fractured bone has been the clavicle, where the clavicle is broken down when the shoulder is struck by the impact of dropping on outstretched hands or through a direct strike. Fractured clavicle treatment is used to treat it. 

Structure

The collarbone is an elongated, double-curved bone that links the arm to the body's trunk. It serves as a strut to hold the scapula in a position such that the arm would swing freely. It is situated right just above the rib. At the sternoclavicular joint, this articulates through the manubrium of the sternum (breastbone). It does have a flattened lateral end as well as a rounded medial end.

Each collarbone bends laterally and anteriorly over approximately half its length from the nearly pyramidal sternal end. The scapula's acromion would then be articulated with an even wider posterior curve. The sternal end of the collarbone is wider than that of the flat acromial end.

A rough inferior surface carries a ridge, slightly rounded projection, as well as the trapezoid line, the conoid tubercle, upon the acromial end. Such specular highlights act as attachment points for shoulder muscles and ligaments.

It is categorized into three sections: the medial end, the lateral end, and the shaft.

Medial End:

The sternal end is another name for it. The sternoclavicular joint is created when the medial edge of the sternum underlines only with the clavicular groove of the manubrium. Through articulation with the very first costal cartilage, the articular surface stretches to an inferior aspect. The convex portion of the medial end is 1/3 of the total area.

Lateral End:

The acromial end is another name for the lateral end. From the top to the bottom, it is flat. The acromioclavicular joint is formed by a facet that articulates mostly with the shoulder. The joint capsule is attached to the region surrounding the joint. The front border is concave outward, while the back border is convex.

Shaft:

The medial two-thirds of the shaft and the lateral one-third are split. The medial section is broader than that of the lateral section.

Lateral One-Third of the Shaft:

The shaft's lateral third features two surfaces as well as two borders.

• The deltoid muscle has its roots on the anterior border, which is concave forward.

• The trapezius muscle is connected to the posterior border, which is convex.

• The inferior surface does have a trapezoid line and a tubercle; the conoid tubercle for connection to the trapezoid and the conoid ligament, which connects the collarbone to the coracoid process of the scapula as a component of the coracoclavicular ligament.

Development:

During the 5th and 6th weeks of pregnancy, the collarbone has been the first bone within the embryo to initiate the process of ossification. Nevertheless, at around 21–25 years of age, it is among the last bones to complete ossification. Intramembranous ossification forms the lateral end, whereas endochondral ossification forms the medial end.

It is made up of a cancellous bone mass encased in a lightweight bone shell. Two ossification hubs, one medial and one lateral merge afterwards to form the cancellous bone. Because a layer of fascia surrounding the bone promotes the ossification of neighbouring tissue, a compact develops. A periosteal collar is a compact bone that results.

Variation:

The clavicle seems to have a more varied shape than many other long bones. A division of the supraclavicular nerve may puncture it on rare occasions. Male clavicles are usually longer and much broader than female clavicles.  A survey of 748 males and 252 females found a 5-6mm (0.20 in and 0.24 in) discrepancy in collarbone length among age brackets 18–20 and 21–25 for males and females, respectively.

• The left clavicle is normally longer and less powerful than the right.

• Cleidocranial dysostosis causes the collarbones to be partially or entirely missing.

• The levator claviculae muscle originates on the transverse processes of the upper cervical vertebrae and inserts in the lateral half of the clavicle in 2–3% of individuals.

Functions:

The collarbone serves a number of purposes:

• It acts as a supporting element from which the scapula and free limb are expelled; this structure holds the upper limb far from the thorax, allowing the arm to travel freely. It enables the scapula to freely travel on the thoracic wall by serving as a flexible crane-like strut.

• It preserves the upper limb's neurovascular complex by protecting the cervicoaxillary canal.

• Physical impacts again from the upper limb are transmitted to the axial skeleton.

Clinical Significance

• Dislocation of the acromioclavicular joint ("AC Separation").

• The clavicle is weakening.

• Osteolysis.

• Dislocations of the sternoclavicular joint.

During a medical test, the midclavicular line, a vertical line drawn from the mid-clavicle, is used to characterise the cardiac apex rhythm. It is also helpful for discovering the gallbladder, which is situated between both the midclavicular line and the transpyloric plane and assessing an expanded liver.