Of the dislocations of the phalanges upon the metacarpus those of the thumb are the more frequent. This may occur as the result of a fall, by which the thumb is forced backward into a position of hyperextension. Nearly all of these dislocations are accompanied by a rupture of capsule. Those of the thumb are difficult of reduction; this appears to be due to the tendons of the short flexor, which surround the head of the metacarpal bone. The sesamoid bones also furnish a source of difficulty, while the long tendons, when contracted by their respective muscles, increase it ([Fig. 354]).
Fig. 354
Metacarpophalangeal dislocation.
Treatment, especially of the thumb dislocations, is facilitated by first exaggerating the abnormal position, then making traction and pressure in the proper direction at the same time. Special forceps have been devised for seizing and holding the digits, or a clove-hitch can be thrown over the thumb or finger. Extension should not be first made in the axis of the metacarpal bone, but rather at an abrupt angle to it in order to relieve the expanded phalangeal end. The majority of writers concede that in some cases reduction is practically impossible. When effort has proved futile the parts should be sterilized and incised, the incision being utilized for open reduction or for excision, as deemed best.
Dislocations of the other phalanges are usually easily recognized and treated by traction and pressure.
DISLOCATIONS OF THE HIP.
Hip dislocations constitute about 5 per cent. of the total. As they are produced by violence they are much more frequent in men, and occur mostly between the ages of twenty and fifty years. Before the twentieth year epiphyseal separations often take place, while after the fiftieth year violence will usually break the neck of the femur. Nevertheless dislocations may occur at any age. The hip is a ball-and-socket joint, with a deep socket still further extended by cartilage, in which the head of the bone is not only retained by the ligamentum teres, but by atmospheric pressure, which in the natural state furnishes a factor of perhaps one hundred pounds. The strongest muscles and tendons of the body envelop the joint. When dislocation occurs the capsule is usually torn along its inferior aspect. The limb is usually in an extreme position, or it would require more violence to tear the head from the socket. The anterior dislocations occur during abduction without outward rotation; posterior dislocations occur during flexion. Thus when a person is stooping over in work and a heavy weight falls upon the back the head of the bone is more easily pushed backward, especially if the feet be close together.
While hip dislocations are classified for convenience, and because of their final form, the head of the bone may rest upon almost any segment of the margin of the acetabulum, though within a short time it will assume a position justifying a designation as anterior or posterior, meaning thereby in front of or behind Nélaton’s line. This is, moreover, a convenient distinction, as the symptoms vary between the two groups. Another classification is into the forward, the backward or backward and upward, and the downward, which are again referred to as iliac, ischiatic, dorsal, and supracotyloid among the posterior, and perineal, obdurator, suprapubic, etc., among the anterior ([Fig. 355]).
Allis, however, has simplified the subject by showing that all forms of dislocation escape primarily from the lower segment, shifting their position later either upward or downward. He classifies them as follows: