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 bony processes are less distinct in children than in adults and fractures sometimes pass unrecognized, being considered sprains, until the persistent disability or marked deformity betrays their presence. Luxations and fractures are at times mistaken for one another. For these reasons a working knowledge of the anatomy of the region is indispensable.
The fractures that occur in this region are transverse fractures above the condyles and oblique fractures through the condyles, which may either involve the condyles proper (epicondyles so called) and be extra-articular, or involve the articular surface of the trochlea or capitellum. Both condyles may be detached by a T- or Y-shaped fracture: the olecranon may be fractured and also the head or neck of the radius.
This is the most frequent fracture of the lower end of the humerus. The mechanism of its production is not settled. There is little doubt but that it can be produced by hyperextension, as the bone fractures at this point when luxation does not occur. Hamilton regarded a blow on the elbow as the cause. The line of fracture runs transversely across the bone just above the condyles and obliquely from behind downward and forward (Fig. 311, page 296).
The lower fragment is drawn upward and backward and sometimes there is an angular lateral deformity with obliteration of the carrying angle (see page 282).
The overriding of the fragment produces shortening of the humerus as measured from the acromion to the lateral (external) condyle. The olecranon projects backward, causing a hollow above which resembles that produced in backward luxation. The flexure of the elbow is fuller than normal. The relation of the condyles to the tip of the olecranon is not altered. The condyles may, however, lie posterior to a line drawn down the middle of the humerus in its long axis. The sharp edge of the lower fragment can sometimes be felt posteriorly.
Extension of the forearm causes the fragment to be pushed still farther upward.
There is no single treatment that is applicable to all cases. If the arm is too much extended, the biceps and brachialis anticus are made tense, and tension of either the anterior or posterior muscles tends to favor overlapping and to prevent replacement. Full flexion renders the triceps tense. To relax both sets of muscles a position at about right angles is probably best.
Stimson has shown that gunstock (angular) deformity frequently follows this injury, hence especial care should be taken to guard against it. It is caused by a tilting of the lower fragment. Instead of a line joining the condyles being at right angles to the long axis of the humerus, it may be oblique, owing to one condyle being higher than the other. Practically it is not possible to recognize this displacement when the arm is bent at a right angle. The splints will fit the part and everything appears satisfactory, but on removal of the splints and extension of the forearm it may be found that the carrying angle has been destroyed and that a gunstock deformity is present. This accident is to be avoided by extending the arm during the earlier periods of treatment before the fragment becomes fixed by callus, and seeing that, on extension, the forearm makes the same angle with the arm as does that of the healthy side.
Fig. 311. - Transverse fracture of the lower end of the humerus above the condyles. The upper fragmen is seen to be displaced forward and the lower fragment with the olecranon is displaced backward. This posterio displacement is increased by tension of the triceps muscle.
The common mode of treatment of supracondylar fractures is the use of anteroposterior splints with the elbow bent at a right angle or sometimes acutely flexed.