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 upper end of the humerus may occur through the anatomical neck, through the tuberosities, detaching one or both, and through the surgical neck just below the tuberosities. These fractures are frequently associated with luxation of the head of the bone.
This occurs as the result of direct violence and most often, though not always, in old people. The line of fracture does not always follow exactly the line of the anatomical neck, but may embrace a portion of the tuberosities. The fracture may or may not be an entirely intracapsular one. The capsule in its upper or outer portion is thickened at its humeral end by more or less blending with the tendons of the muscles which pass over it. The capsule at this point is attached to the anatomical neck almost or quite up to the articular surface. On the under side to the contrary it passes about a centimetre below the articular surface and doubles back to be attached somewhat closer to it (see Fig. 266, page 253).
In consequence of this arrangement, a fracture which follows the anatomical neck would be within the joint below and just outside of it above. As a matter of fact, some of these fractures are intra- and some partly extracapsular. This influences the amount and character of the displacement and the course of healing. If the fracture is entirely intracapsular, bony union may not occur, as no callus may be thrown out by the upper fragment and atrophy of the fragment may ensue. The fragment is apt to be much displaced, being tilted and lying to the inner side anteriorly. Sometimes it is entirely extruded from the joint. In one case we have seen it lodged in front under the anterior axillary fold.
The signs and symptoms will vary much, according to the position of the head, and a positive diagnosis may be impossible. A thorough knowledge of the surface anatomy is essential in these cases and a careful comparison should be made with the opposite healthy shoulder. Impaction sometimes occurs, and is said to be most often of the upper fragment into the lower, sometimes splitting it and detaching to a certain extent one of the tuberosities. Sometimes it is the lower fragment which is impacted into the upper.
Like the former these are often accompanied by luxation, especially if one or both of the tuberosities is detached. These fractures are frequently blended with fracture through the anatomical neck. In this fracture, however, the influence of the muscles is to be remembered. The supra-spinatus, infraspinatus, and teres minor insert into the greater tuberosity, and the subscapulars into the lesser. The line of fracture may pass through their insertions and the displacement may be slight. The upper fragment is, however, liable to be tilted outward by the contraction of the supraspinatus muscle, which is attached to the upper portion of the upper fragment, while there is no muscle attached below to counteract it. In this case the shaft of the humerus is drawn up and out by the deltoid and is felt beneath the acromion process. There is but little rotatory displacement of the upper fragment because the subscapulars anteriorly is neutralized by the infraspinatus and teres minor posteriorly.
In those instances in which there is not much displacement of the upper fragment, the lower one may be drawn inward and forward by the action of the muscles of the axillary folds.
Fractures detaching the tuberosities are almost always accompanied by luxation. If the greater tuberosity alone is detached, it is drawn up beneath the acromion by the supraspinatus.
In all these fractures the subsequent disability is often great and the prognosis is unfavorable. They are amongst the hardest in the body to correctly diagnose. They are treated sometimes with a shoulder-cap and sometimes with the arm in the abducted position while the patient is kept in bed. Epiphyseal separation will be alluded to farther on.