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.
Reduction of an anterior luxation of the shoulder can be accomplished in two ways, viz., the direct, in which the head is pulled or pushed back into the socket, and the indirect, in which it is levered back.
This consists in first placing the arm in approximately the position it occupied when luxated (abduction) and then pulling or pushing the head toward and into the socket while the arm is rotated to relax the capsule and allow the head to enter. The usual obstacle to reduction of a recent luxation is muscular contraction. The main muscles acting are the deltoid, pectoralis major, latissimus dorsi, and teres major. To effect reduction the action of these muscles must either be held in abeyance or overcome by force. This may be accomplished in several ways, viz., by the use of general anaesthesia, by such gentle manipulations as will not incite the muscles to contraction, by a quick movement accomplishing the object before the muscles are able to contract, or, finally, by overcoming the muscular action by steady continuous traction. General anaesthesia is the surest way of obviating muscular contraction.
The question of muscular contraction having been solved by one or more of these expedients the actual replacement is to be accomplished by dragging or pushing the head back over the route it took in coming out. The opening in the capsule is below and anterior, therefore the arm is to be strongly abducted, and traction made upward and backward. This drags the head upward and backward over the rim of the glenoid cavity into its socket. If it does not enter readily it is because of tension of the untorn part of the capsule; this is to be remedied by gently rotating the arm, when the proper position will be revealed by the slipping of the head into place. Rotation in either direction beyond the proper point narrows the tear in the capsule and keeps the head from entering. Traction is necessary in order to replace the head of the humerus on its pedestal or shoulder-girdle from which it has fallen onto the side of the chest (see Figs. 248 and 250).
Fig. 249. - Subcoracoid dislocation of the shoulder. Dissection showing the relation of the muscles to the displaced humerus.
If it is desired to tire the muscles out, the plan of Stimson is best. Place the patient in a canvas hammock and allow the arm to hang downward through a hole in the canvas. Fasten a ten-pound weight to the wrist and inside of six minutes the weight will have dragged the head of the humerus into place. This same object can be carried out, but not so well, by having the patient lie on the floor and pulling the arm directly upward by means of a rope and pulley. Here the weight of the body acts as the counter force.
Other means, such as the heel in the axilla, etc., may be found described in works on surgery, but it is to be remembered that the objects to be sought are (1) to overcome the action of the deltoid by abducting the arm, (2) to overcome the axillary muscles - pectoralis major, latissimus dorsi, and teres major - by traction, and (3) to loosen the capsule and open the tear to its widest extent by rotation while the head is pushed with the hand toward and over the lower and anterior edge of the socket.
Fig. 250. - Diagram to show how rotation influences the size of the rent in the capsule. The square represents the rent in the capsule and the circle the head of the humerus. If the humerus is rotated too much in the direction of the arrows, either to the right or left, the opening in the capsule is so narrowed as to obstruct the passage of the head.