The slender S-shaped clavicle (derived from latin word clāvis meaning key) is the only direct skeletal attachment between trunk and the upper limb. Other names for Clavicle are:
- Collar bone
- Beauty bone
Peculiarities of Clavicle:
- It has no medullary cavity
- It is the first bone to ossify in the fetus (5th-6th week)
- It is the only long bone having 2 primary centers of ossification (others have only 1)
- It is the only long bone that ossifies in membrane and not in cartilage
- It is the only long bone lying horizontally
- It is the most common fractured long bone in the body
- It is subcutaneous throughout
Anatomy of Clavicle:
The bone has a cylindrical part called the shaft, and two ends: lateral and medial.
1. Lateral 1/3: flattened in section and thinner
- consists of 2 borders : anterior and posterior and 2 surfaces: superior and inferior
- anterior border: concave forwards and gives origin to deltoid muscle
- posterior border: convex backwards and gives attachment to trapezius muscle
- superior surface: is subcutaneous
- inferior surface: shows conoid tubercle and trapezoid ridge which gives attachment to conoid ligament (medial part of coracoclavicular ligament) and trapezoid ligament (lateral part of coracoclavicular ligament) respectively
2. Medial 2/3: circular in section and thicker
- consists of 4 surfaces
- anterior surface: convex forwards and gives origin to pectoralis major
- posterior surface: concave backwards and gives origin to sternohyoid muscle
- superior surface: is rough on its medial part
- inferior surface: has rough oval impression at the medial end for costoclavicular ligament and shows subclavian groove which gives attachment to subclavius muscle
1. Lateral (Acromial) End:
- articulates with with the acromian process of the scapula to form the acromioclavicular joint
2. Medial (Sternal) End:
- articulates with the clavicular notch of the manubrium sterni to form sternoclavicular joint
The clavicle is made up of a medial two-thirds which is circular in section and convex anteriorly, and a lateral one-third which is flattened in section and convex posteriorly.
Medially it articulates with the manubrium at the sternoclavicular joint (this joint containing an articular disc), and is also attached to, the first costal cartilage by the costoclavicular ligament.
Laterally it articulates with the acromion at the acromioclavicular joint (the joint containing an incomplete articular disc) and, in addition, is attached to the coracoid process by the tough coracoclavicular ligament.
The third parts of the subclavian vessels and the trunks of the brachial plexus pass behind the medial third of the shaft of the clavicle, separated only by the thin subclavius muscle. Rarely, these vessels (protected by the subclavius) are torn by the fragments of a fractured clavicle.
Posterior relations of Sternal end of clavicle:
- Behind the sternoclavicular joints lie the common carotid artery on the left and the bifurcation of the brachiocephalic artery on the right.
- The internal jugular vein lies a little more laterally on either side.
- These vessels are separated from bone by the strap muscles: the sternohyoid and sternothyroid.
How can you distinguish a left clavicle from right?
- Lateral end is flat and thinner and medial end is round and thicker.
- There is a groove on inferior surface.
- Medial part of shaft is convex anteriorly while lateral part is concave anteriorly.
- Occasionally, the clavicle is pierced by a branch of the supraclavicular nerve.
- The clavicle is thicker and more curved in manual workers, and the sites of muscular attachments are more marked.
- The right clavicle is usually stronger and shorter than the left clavicle.
- In females, the clavicle is shorter, lighter, thinner, smoother and less curved compared to males
- In females, the lateral end of the clavicle is little below the medial end; in males the lateral end is either at the same level or slightly higher than the medial end
a) Functions of clavicle:
- To transmit forces from the upper limb to the axial skeleton
- To act as a strut holding the arm free from the trunk, to hang supported principally by trapezius
- To provide attachment for muscles
b) Weakest point of clavicle:
- Junction of middle 2/3 and lateral 1/3 (junction between 2 curvatures) is the weakest point of clavicle and hence is the most vulnerable part to fracture.
c) Cause of Clavicle fracture:
- Transmission of forces to the axial skeleton in falls on the shoulder or hand may prove greater than the strength of the bone at this site and this indirect force is the usual cause of fracture.
d) Clincial features of Clavicle fracture:
- When fracture occurs, the trapezius is unable to support the weight of the arm so that the characteristic picture of the patient with a fractured clavicle is that of a man supporting his sagging upper limb with his opposite hand.
- Because the clavicle is directly beneath the skin and is not covered with muscle, a fracture can easily be palpated, and frequently seen.
e) Anatomical Basis:
- Fractured lateral fragment: depressed (downward displacement by gravity) and drawn medially (adducted by spasm of the shoulder adductors, principally the teres major, latissimus dorsi and pectoralis major)
- Fractured medial fragment: slight elevation by sternocleidomastoid
2) Cleidocranial dysostosis:
- The clavicles may be congenitally absent or imperfectly developed in a disease called cleidocranial dysostosis.
- In this condition, the shoulders droop, and can be approximated anteriorly in front of the chest.
Anatomical demonstration clavicle: