The cardinal indications of a dislocation are deformity with alteration in contour and position of the affected joint. It usually happens that the dislocated bone ends cannot be felt in normal position, but are felt somewhere else in the vicinity. About the shoulder and hip of stout or fat individuals it may not be easy to feel the head of the bone, but unless the case be complicated by a fracture it can usually be detected by aid of anesthesia. The deformity may include a lengthening or shortening of the limb, apparent or real, as well as abnormal eversion or inversion, or other peculiarity of position.
Whatever alterations in position appear will be accentuated by spasm of the muscles which pertain to the movement of the affected joint or even of the entire limb. These are usually so tightly contracted as to form a complicating feature of such cases and to lead to that loss of mobility which is diagnostic of every dislocation. Limitation of motion is not entirely a matter of muscle spasm. It is not under voluntary control and subsides only under anesthesia. To some extent motion may be limited by escape of the head of a bone through a small rent in the enveloping capsule, by which it is afterward tightly clasped. This is particularly true of the shoulder and hip. Certain dislocations of the fingers or thumbs are also made more rigid by fixation of the tendons, which become tightly stretched within the neighboring tendon sheaths.
A sort of crepitus, which may be easily mistaken for that of fracture, is occasionally detected during the examination of a dislocated joint. It lacks the peculiar grating character of true bony crepitus.
In addition to these features there are certain subjective symptoms, of which loss of function is the most prominent, while pain is a more or less frequent but variable accompaniment, and dependent on the amount of tissue injury or pressure upon nerves. Moreover, the displacement once completely rectified (“reduced”) does not tend to recur, as is the case with fractures.
PATHOLOGICAL AND CONGENITAL LUXATIONS.
The statements made above refer almost entirely to recent and traumatic dislocations.
Pathological dislocations are those which are produced gradually and through the mechanism of disease affecting the joint structures. The head of the bone is gradually drawn out of the acetabulum, in tonic spasm of hip-joint disease, by the continuous action of muscles, the result being the complete displacement of the bone from its original socket, or what is known, at the hip, as the migration of the acetabulum, where its upper margin, being softened by disease, is gradually extended and altered, so that the femoral head rests an inch or more higher upon the side of the pelvis than is normal. Pathological dislocations, then, may occur both in the course of the infectious joint diseases as well as in the neuropathic.
Congenital luxations are those which occur from defect in the shape or arrangement of joint structures, permitting a departure from the normal standard. While no joint in the body is exempt from abnormalities of this description, the congenital hip dislocations are those which have attracted attention by their frequency and the disability which they produce.
While the general character of these changes is easily made out by the ordinary methods of examination, coupled with a suitable history, a well-made skiagram will tell at a glance a story which it may take some effort to elicit by other means; hence radiography has here been of great value to the surgeon. Congenital dislocations are devoid of nearly all the features which characterize traumatic dislocations, and their consideration will be found in the chapter on Orthopedics.
Differential diagnosis as between fractures and dislocations is not always easy. Furthermore it is frequently the separation of a prominence by fracture which permits of dislocation, this being particularly true of the elbow and the ankle. The extent of a fracture may seriously complicate the problem of treatment, as, for instance, when the head of the humerus is not only dislocated below the clavicle but separated from the shaft by fracture at the surgical neck. A dislocation made possible only by fracture will not remain reduced as will one which is simple and uncomplicated, while it will display even a greater amount of motility and displacement. Other complications may occur, many of which are common both to dislocations and to fractures in the vicinity of joints, such as lacerations of bloodvessels or nerve trunks, pressure upon the latter, compound injuries with infections, etc.