CASE I. A man fell in descending a ladder, and luxated his humerus in a downward direction. Desault being immediately called, discovered the nature of the disease, but deferred the reduction till evening. In the interval, the patient went to get into a chaise: his foot slipped, and he fell a second time. The pains became more severe than at the time of the first accident; and Desault, on his return, instead of finding, as in the morning, the head of the humerus under the hollow of the arm-pit, discovered it to be behind the pectoralis major.
26. Muscular action is one permanent cause of a new displacement. Suppose the humerus luxated downward, the pectoralis major, and the deltoid muscles draw its superior extremity upward and inward, which, offering to their action but a feeble resistance, changes its position and that in a two-fold direction.
27. The different motions of the arm may also, according to their direction, produce the same effect. Thus we have often witnessed a luxation inwards succeeding to a luxation downwards, in consequence of unskilful attempts to reduce it.
28. The diagnosis of luxations of the humerus, presents in general, but few difficulties.
Whatever may be the mode or seat of the displacement, there always exists, as Hippocrates has observed, a manifest depression under the acromion, which exhibits a prominence more perceptible than in its natural state. The motions of the part are almost all accompanied with pain; the greater part of them are impracticable; all of them very much confined. The arm cannot move, without a synchronous motion of the shoulder, because, the articulation being no longer able to exercise its functions, these two parts constitute, so to speak, but one body.
29. Besides these signs, which characterize generally every species of luxation of the humerus, each species is marked by certain others peculiar to itself. If the displacement be downward, the arm is a little longer than in its natural state; it can be moved gently outwards; but an acute pain is the inevitable consequence of moving it forward or backward. The elbow is more or less removed from the axis of the body, by the action of the deltoid, the long portion of the biceps, and the supra-spinatus muscles, which, being unnaturally stretched, contract themselves and tend to carry the bone outward. The pains which result from this position, force the patient, in order to relieve them, to lean towards the affected side, to keep the fore-arm half-bent, the elbow resting on the hip, so that the arm, finding a place of support, may be freed from the painful movements, and from the disagreeable sensation produced by its own weight. From this attitude alone, was Desault in the habit of discovering luxations in a downward direction, and was rarely mistaken in his diagnosis. It is thus, that, in a fracture of the clavicle, the inclined position of the patient is oftentimes, at first sight, characteristic of the nature of his complaint. Beneath the hollow of the arm-pit there always exists a protuberance more or less perceptible, formed by the head of the humerus.