The comprehension of the causes which produce this constrained attitude and restricted motion, while of great as sistance in diagnosis, is, in many cases, absolutely essential to intelligent manip ulative treatment, for those same forces that aid our diagnosis we must take into account in our efforts to effect reduction. These forces are purely mechanical. The dislocated bone plays the part of a lever whose long arm extends from the attach ment of certain ligaments to its distal extremity and whose short arm is that part of the bone between this point of attachment and the head of the bone.
The figure shows how the ligaments opposite the side toward which the bone has been displaced are put on the stretch by attempts to move the lower part of the limb in the same direction, so long as the head of the bone impinges upon the outer edge of the articular surface or some similar obstacle. Hence the abnormal attitude and restriction of motion in some directions—and possibly abnormal mobility in others, be it noted—and hence, also, the inference that such an obstacle is not to be overcome by brute force, but rather by strategy and dex terity.
Shortening or lessening of a limb is another aspect of the deformity. As a sign, however, it is most unreliable. Fig. 2 indicates the relative positions of the bones in a subcoracoid dislocation of the shoulder as compared with the normal joint. With the arm abducted, the short ening is marked, but in adduction there is little or no shortening; indeed, there may be some lengthening.
Crepitation of a fibrous quality may be elicited during manipulation by friction of the bone over fibrous or cartilaginous structures, and means nothing. True bony crepitus m.eans, of course, a fract tire.
Pain is always present, and is due to two causes. There is the primary pain caused by the laceration of the tissues at the moment of the dislocation. This soon passes away. Any persistent pain is due to pressure on nerves, and can only be relieved by the removal of that press ure.
Loss of Function.—This is usually complete, and due partly to the pain and partly to the fixation caused by the changed relations of the bones.
Symptoms of Old Unreduced Disloca tions.—Deformity of contour and atti tude, as well as restriction of motion, will persist as long as the dislocation remains unreduced; but, as the parts tend to adapt themselves to their altered condi tions, the disability becomes progress ively less, as a general rule, until the functions of the limb can be fairly-well performed. But several conditions may
interfere with this restoration of func tion. An excessive production of callus may limit the motions of the joint or even ankylose it in an awkward position; the head of the bone may be progress ively displaced farther from its normal situation, and the disability thus become greater instead of less; or an intractable neuralgia or cedema may result from pressure on adjoining nerves or vessels.
Diagnosis. — The one demonstrative sign of dislocation is the recognized pres ence of the head of the dislocated bone in an abnormal position. One may make the same inference from the negative evi dence; namely, the absence of the head of the bone from its normal situation. Thus, in backward dislocation of the ribs or the sternum the diagnosis is made by the absence of the heads of the bones from where they should be, and not by their presence where they should not be.
In such localities as the fingers or knee the head of the bone may be seen; else where it may be felt, as in the jaw (for ward) or the shoulder; or, again, the diagnosis may only be ascertained by finding an indefinite mass which par takes of the motions imparted to the bone. Measurements may help; but, as above noted, are liable to be fallacious.
In typical dislocations the attitude of the limb and the limitation of motion are usually the first hint the surgeon ob tains of the nature of the case; but, we repeat, the only conclusive evidence is the discovery of the head of the bone out of its normal place.
—The dif ferentiation of a simple dislocation from a fracture at or near the articular surfaces is often difficult, sometimes impossible. If the fracture is through the neck of the bone (without impaction) the dislocated head will not move with rnotions im parted to the shaft of the bone; but will, on the contrary, give rise to a bony crep itus, unless some soft parts are inter posed. But if the fracture consists sim ply of the splintering of an articular edge, or the tearing off of a tuberosity, the fragment may be pushed or drawn away and give no evidence, except per haps a weakness in the joint, a lack of certain motions, or a tendency to recur rence of the dislocation, for which we can only assign the fracture as a probable cause.