CLAVICLE

The clavicle is a sigmoid-shaped long bone with a convex surface along its medial end when observed from cephalad position. It connects axial and appendicular skeleton. It supports shoulder so that arm can swing clearly away from the trunk. Clavicle transmits weight of the limb to the sternum. 

 It receives its name from the Latin clavicula ("little key"), because the bone rotates along its axis like a key when the shoulder is abducted. Clavicle has a shaft and two ends.

SHAFT

The shaft is further divided in lateral one-third & medial two-thirds. 

Lateral one-third: It is flattened from above downwards. It has 2 borders and 2 surfaces.

The anterior border is concave forwards which gives origin to Deltoid muscle and Posterior border is convex backwards which gives origin to Trapezius muscle.

The superior surface is subcutaneous and the inferior surface has a ridge called the trapezoid line and a tubercle; the conoid tubercle for attachment with the trapezoid and the conoid ligament, part of the coracoclavicular ligament that serves to connect the collarbone with the coracoid process of the scapula.

Medial two-thirds: It is rounded and said to have 4 surfaces. The Anterior is convex forwards, Posterior has smooth surface, Superior surface is rough in medial part and & Inferior surface has a rough oval impression at the medial end.The lateral half of this surface has a longitudinal subclavian groove in which nutrient foraman lies.

LATERAL END & MEDIAL END

The lateral end is also known as the acromial end. It is flat from above downward. It bears a facet that articulates with the shoulder to form the acromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and posterior border is convex backward.

It is also known as the sternal end. The medial end is quadrangular and articulates with the clavicular notch of the manubrium of the sternum to form the sternoclavicular joint. The articular surface extends to the inferior aspect for articulation with the first costal cartilage.

Right clavicle - Superior aspect

      Right Clavicle - Inferior aspect

SIDE DETERMINATION

The side to which a clavicle belongs can be determined from the following characters:

1. The lateral end is flat, and the medial end is large and quadrilateral.

2. The shaft is slightly curved, so that it is convex forwards in its medial two-thirds, and concave forwards in its lateral one-third.

3. The inferior surface is grooved longitudinally in its middle one-third.

SEX DETERMINATION

1. In females, the clavicle is shorter, lighter, thinner, smoother, and less curved than in males.

2. The midshaft circumference and the weight of the clavicle are reliable criteria for sexing the clavicle.

3. In females, the lateral end of the clavicle is a little below the medial end; in males, the lateral end is either at the same level or slightly higher than the medial end.

DEVELOPMENT AND OSSIFICATION

The collarbone is the first bone to begin the process of ossification (laying down of minerals onto a preformed matrix) during development of the embryo, during the fifth and sixth weeks of gestation. However, it is one of the last bones to finish ossification at about 21–25 years of age. Its lateral end is formed by intramembranous ossification while medially it is formed by endochondral ossification. It consists of a mass of cancellous bone surrounded by a compact bone shell. The cancellous bone forms via two ossification centres, one medial and one lateral, which fuse later on. The compact forms as the layer of fascia covering the bone stimulates the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.

Even though it is classified as a long bone, the collarbone has no medullary (bone marrow) cavity like other long bones, though this is not always true. It is made up of spongy cancellous bone with a shell of compact bone. It is a dermal bone derived from elements originally attached to the skull.

MUSCLES AND LIGAMENTS ATTACHMENT

   1.At the lateral end the margin of the articular surface for the acromioclavicular joint gives attachment to the joint capsule.

   2.At the medial end the margin of the articular surface for the sternum gives attachment to:

(a) the fibrous capsule all round

(b) the articular disc posterosuperiorly

(c) the interclavicular ligament superiorly.

   3.Lateral one-third of shaft

(a)The anterior border gives origin to the deltoid.

(b)The posterior border provides insertion to the trapezius.

(c) The conoid tubercle and trapezoid ridge give attachment to the conoid and trapezoid parts of the coracoclavicular ligament.

   4. Medial two-thirds of the shaft

(a)The anterior surface gives origin to the pectoralis major.

(b)The rough superior surface gives origin to the clavicular head of the stemocleidomastoid.

(c)The oval impression on the inferior surface at the medial end gives attachment to the costoclavicular ligament.

(d)The subclavian groove gives insertion to the subclavius muscle. The margins of the groove give attachment to the clavipectoral fascia.

The nutrient foramen transmits a branch of the suprascapular artery.