This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Fractures of the clavicle divide with those of the radius the distinction of being the most frequent of any in the body.
The clavicle is most often broken in its middle third, next in its outer, and, lastly, in its inner third.
This is the rarest fracture of the clavicle and has its main anatomical interest in relation to the costoclavicular ligament. This ligament runs obliquely upward and outward from the upper surface of the cartilage of the first rib to the lower surface of the clavicle, a distance of 2 cm. (i in.).
Immediately in front of the outer portion of this ligament is the insertion of the tendon of the subclavius muscle. The line of the fracture may be either transverse or oblique; if oblique it follows the same direction as do the fractures of the middle third of the bone, viz., from above, downward and inward. The displacement of the inner fragment is upward and of the outer fragment downward. The displacement of the inner fragment upward is promoted by the attachment of the clavicular origin of the sternomastoid muscle: it is opposed by the costoclavicular (rhomboid) ligament and to a less extent by the subclavius muscle.
Fig. 256. - Fracture of the clavicle just outside of the middle, with the customary deformity.
The clavicle is most frequently broken in the outer half of its middle third. The bone at this part is most slender; it is here that the anterior curve passes into the posterior; and, finally, it has fewer muscular attachments at this situation. The upper surface has arising from its inner third the clavicular origin of the sternomastoid muscle. Its middle third has no muscular attachments, and on its outer third is the trapezius muscle. On the lower or anterior surface on its inner half is the clavicular origin of the pectoralis major and on its outer third is the deltoid. This leaves the outer half of the middle third free from muscular attachments, with the exception of the subclavius on its under surface. It is through this part of the bone that fractures occur.
Sometimes in children the line of fracture is transverse, but most often it is oblique and always in the direction from above downward and inward.
The displacement of the inner fragment is upward, and of the outer fragment downward and inward. This produces the deformity seen in Fig. 256. The inner fragment is pulled up by the clavicular origin of the sternomastoid muscle. The support of the clavicle being gone, the shoulder falls down and in. It is impelled in that direction, first, by the weight of the upper extremity, and, secondly, by the action of the axillary fold muscles, - pectoralis major and minor anteriorly and teres major and latissimus dorsi posteriorly, and by the subclavius to some extent. The anterior • edge of the scapula rotates inward and its posterior edge tilts outward.
In this manner overlapping is produced, and measurements of the injured and healthy sides taken from the sternoclavicular to the acromioclavicular joint will show some shortening on the injured side. As the continuity of the shoulder-girdle 16 has been destroyed and its prop-like action lost, its function of abduction ceases, and the patient is unable properly to elevate the arm. Sometimes the brachial plexus or subclavian vessels are injured by the inner end of the outer fragment. The artery passes beneath the middle of the bone, the vein being to its inner side and the brachial plexus to its outer side. We have operated on one such case of injury to the brachial plexus; and cases of haematoma arising from injury to the veins and aneurism from injury to the artery have been recorded.
Fig. 257. - Fracture of the clavicle just outside the middle. The outer fragment is displaced downward and inward and the inner fragment upward. The brachial plexus and subclavian vessels are behind the inner end of the outer fragment.