The patella once displaced the joint structures are left more or less permanently impaired, and recurrence of the lesion is by no means uncommon. Some individuals, the young especially, have the habit of “slipping the knee-pan,” this implying that at least partial displacement occurs easily with comparatively slight provocation. Sometimes children become so accustomed to this that they learn how to care for it themselves.
Treatment.
—After every knee dislocation protection should be afforded for a considerable period. In habitual dislocations it may be justifiable to make lateral incisions and to excise an elliptical portion of the capsule, by which its dimensions may be reduced and its undue laxity abolished.
DISLOCATIONS OF THE KNEE.
The head of the tibia is occasionally displaced as the result of accident, though frequently this is the result of joint lesions. A traumatic dislocation can scarcely occur without considerable injury and internal derangement of the joint structures proper. Anterior dislocation may occur when the femur is forced backward or the leg forward in severe accidents. Here the popliteal vessels may undergo such pressure and injury as to constitute a serious complication. The backward dislocations are less common, though likewise the result of violence. It matters not whether the thigh be fixed and the leg forced in either direction, or whether the leg be caught and fixed while the body is made to displace the femur; such injuries are not likely to be mistaken. They are likely, also, to be accompanied by displacement of the semilunar cartilages. Lateral dislocations are practically the result of force, often combined with torsion. Injury to the lateral ligaments, usually extensive laceration, should accompany them.
Dislocations of the knee are more or less easily reduced, in theory at least, by forcible traction and manipulation, and with the aid of an anesthetic. Absolute rest, preferably in a plaster-of-Paris splint, is requisite.
The semilunar cartilages are occasionally torn loose and more or less displaced, either toward the notch or toward the exterior of the joint. A cartilage so displaced will project, as a rule, at the upper margin of the tibia. These injuries may occur alone or as a complication of more serious forms described above.
Symptoms.
—These displaced cartilages produce symptoms simulating those of movable bodies in the joint—that is, disability depending upon the extent of the original injury and the direction of the displacement. The movable cartilage may be either pulled into place by flexion or manipulated until it returns there, but will frequently reappear when the leg is straightened. It sometimes becomes so entangled in the joint as to cause almost complete disability. When movable anteriorly it may be recognized along the upper border of the tibia. The same sudden disability may be produced here as when there are other loose or movable bodies in the joint. The patient may be able to indicate that there is something movable in the joint.