Page 184 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 169

The bones and joints of the upper limb 169

2◊◊It is the first to ossify in the fetus (5th–6th week).
3◊◊Although a long bone, it develops in membrane and not in
cartilage.
4◊◊It is the most commonly fractured long bone in the body.
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; this was the
cause of death of Sir Robert Peel following a fall from his horse.
The sternal end of the clavicle has important posteror relations; 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.

Clinical features

The clavicle has three functions:
1◊◊to transmit forces from the upper limb to the axial skeleton;
2◊◊to act as a strut holding the arm free from the trunk, to hang supported
principally by trapezius;
3◊◊to provide attachment for muscles.
The weakest point along the clavicle is the junction of the middle
and outer third. 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.
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. The lateral fragment is not only depressed but also drawn
medially by the shoulder adductors, principally the teres major, latissimus
dorsi and pectoralis major (Fig. 121).

The humerus (Fig. 122)
The upper end of the humerus consists of a head (one-third of a sphere)
facing medially, upwards and backwards, separated from the greater and
lesser tubercles by the anatomical neck. The tubercles, in turn, are separated by