Those which occur at the upper end may be classified as (a) anatomical neck ; (b) through the tubercles ; (c) separation of the upper epiphysis ; (d) surgical neck.
(a) Anatomical Neck-This is a rare form of fracture. As the capsule extends beyond the anatomical neck below, this fracture is partly intracapsular. If entirely separated, the head dies ; but if it is impacted into the broad upper end of the shaft, or the reflected fibres from the capsule remain intact, it may live. The deltoid may be slightly flattened, and the upper end of the lower fragment projected slightly forwards and inwards.
(b) Fractures through the tubercles frequently cause but little displacement, owing to the broad bone surfaces and the muscular insertions through which the fracture passes. There are three epiphyses for the upper end of the humerus-one for the head, and one for each tuberosity, which fuse together about the fifth and join the shaft about the twenty-first year.
(c) Separation of the upper epiphysis occurs just about the position of fracture through the surgical neck. Displacement is generally slight owing to the broad surfaces, the upper end of the lower fragment perhaps forming a slight projection below the coracoid process. Marked shortening is apt to follow this fracture, as the humerus grows chiefly from this upper epiphysis.
(d) Surgical Neck-Fracture in this situation is fairly common, and impaction may occur, the lower being driven into the upper fragment. While there may be a tendency for the upper fragment to be abducted and rotated outwards by the spinati and teres minor muscles, and for the upper end of the lower fragment to be drawn upwards by the deltoid, biceps, coraco - brachialis, and triceps, and inwards and forwards by the great pectoral, there is often little or no displacement.
The shaft ossifies from a single centre, and is partially ossified at birth. Fractures of the shaft may be classified according as they occur above or below the insertion of the deltoid. They are generally due to direct violence, and displacement depends more upon the fracturing force than on muscular action. In fracture aoove the insertion of the deltoid the lower end of the upper fragment is drawn in by the pectoralis major, teres major, and latissimus dorsi, while the upper end of the lower fragment is drawn up by the biceps, coraco-brachialis, and triceps, assisted by the deltoid, which also throws it outwards. In fracture below the insertion of the deltoid the tendency to displacement from muscular action is less than in that above the deltoid insertion. The lower end of the upper fragment is carried outwards by the deltoid, and the upper end of the lower fragment upwards by the biceps and triceps. Fracture by muscular action occurs generally below the insertion of the deltoid. These fractures of the shaft are stated to be very frequently followed by nonunion, but this is probably due to the use of faulty apparatus, which does not fix the shoulder and elbow joints, and to dipping of muscular tissue between the broken ends. The most common complication of fracture of the shaft is drop-wrist, due to injury to the musculo-spiral nerve, either at the time of the accident or subsequently from involvement in callus.