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.
The sternal end of the clavicle is most commonly dislocated forward. Other dislocations, which may be upward or backward, are very rare. The range of movement of the clavicle approximates 60 degrees.
The bone is lowest when the elbow is brought forward across the front of the body and highest when the arm is raised and placed behind the neck. The luxation is produced by the shoulder being violently depressed and pushed backward, as in falling on it; in some cases an inward thrust may be added. As the clavicle descends its under surface comes into contact with the first rib, which acts as a fulcrum, and the inner extremity is lifted upward and forward, rupturing the sternoclavicular ligaments. The rhomboid ligament remaining intact prevents a wider displacement of the bone.
As regards treatment, to reduce the luxation the shoulder should be elevated and drawn outward and backward. While pressure is made on the protruding bone the arm is used as a lever and the bone tilted into place. Usually reduction can be readily accomplished, but most people have found it difficult to retain the parts in place. The only sure way of doing so is to keep the patient in bed on his back. Stimson, following Velpeau and Malgaigne, advises the application of an anterior figure eight bandage of plaster of Paris; Hamilton says deformity remains after any method of treatment, but that function will be but little impaired.
Fig. 243. - Dislocation of the sternal end of the clavicle upward and forward, showing how the first rib acts as a fulcrum and the clavicle as a lever.
In upward dislocations the case of R. W. Smith has shown that the end of the bone passes behind the sternal origin of the sternomastoid muscle.
In backward dislocations pressure on the trachea and oesophagus have caused difficulty in breathing and swallowing; cyanosis due to pressure on the internal jugular vein has been observed in one case. When one recalls the function of the clavicle in keeping the shoulder out from the body, it is readily seen that when the security of its inner attachment has once been destroyed displacement is favored by the weight of the upper extremity as well as by the action of all the muscles which pass from the head, neck, and trunk to the shoulder-girdle and humerus.
In these dislocations of the sternal end of the clavicle the fibrocartilaginous disk of the joint sometimes is carried out with the clavicle and sometimes remains attached to the sternum, more often it follows the clavicle.
The acromial end of the clavicle may be dislocated either upward or downward. Nearly all the dislocations are upward.
The displacement is usually produced by direct violence, a blow on the top or back of the shoulder driving the acromion down and inward. The clavicle not only rises but also goes backward, or the scapula comes forward, so that the end of the clavicle may rest on the acromion process. In this dislocation the base of the cora-coid process, on which the clavicle rests and to which it is bound by the conoid and trapezoid ligaments, acts as a fulcrum. The scapula rotates on an anteroposterior axis, passing through the base of the coracoid process, and as the inner portion of the bone rises, its outer portion, - that is, the acromion process, - descends and is torn from the outer end of the clavicle.
Fig. 244. - Luxation of the outer end of the clavicle upward, showing the coracoid process acting as a fulcrum. As the outer end of the clavicle rises, the lower angle of the scapula is carried toward the median line and the acromion process is depressed and torn loose from the clavicle above.
The deformity produced by the upwardly projecting end of the clavicle is typical. The luxation may be complete or incomplete. When incomplete the injury is confined to the acromioclavicular joint; when complete the conoid and trapezoid ligaments are partially or wholly ruptured.
The joint usually possesses a poorly developed fibrocartilage and inclines upward and outward so that the inclination favors the rise of the clavicle. When the conoid and trapezoid ligaments are not ruptured they serve as the axis on which the scapula rotates forward so that the outer end of the clavicle slips backward on the acromion process. This led Hamilton to describe these luxations as backward luxations. In rare instances the end of the clavicle seems to be displaced posteriorly without rising above its normal level. We reported one such case in the Annals of Surgery several years ago. Reduction of the displacement is easily effected, but the same difficulty in keeping the bone in place has been experienced in this dislocation as in dislocations of the inner extremity. Bandages going over the shoulder and down the arm and under the elbow are commonly employed. The only sure way of keeping the clavicle in its proper position is to operate and fasten it to the acromion with wire or chromicised catgut. When the patient is put in bed the bones are readily replaced.
Downward dislocatioin though rare does seem to have sometimes occurred. From the fact of the under surface of the clavicle resting almost or quite on the coracoid process it is difficult to see how it is possible for this injury to take place. It must take place while the scapula is violently twisted on the clavicle. The displacement is readily reduced and shows but little tendency to recurrence.