DISLOCATIONS OF THE KNEE.—These occur rarely and, in order of frequency; forward, backward, outward, inward, and by rotation. The dislocation is fre quently compound, and the prognosis rendered much more grave by a compli cating injury to either of the popliteal nerves or to the popliteal vessels. Even if, after reduction, pulsation reappear in the arteries of the foot, gangrene may supervene from thrombosis caused by laceration of the inner coats of the artery.
Forward dislocation may be complete, or, more commonly, incomplete. When conaplete, the tibia may be displaced some distance upward over the front of the condyles. If the dislocation is com pound, the wound is posterior and trans verse. The cause is direct yiolence or hyperextension of the knee. Reduction is easily made by traction and pressure.
Backward dislocations may be com plete or incomplete. The leg is usually either extended or hyperextended, and may be deviated to one side. The patella
may be dislocated outward. The usual cause is direct violence. Reduction is effected by traction and pressure. Even without reduction a fairly-useful limb has resulted in several cases.
Lateral dislocations are outward or in ward, complete or incomplete. The pa tella is usually deviated toward the side of the dislocation. The incomplete form is usually caused by abduction or (in ward) by adduction. Reduction by trac tion and pressure. Dislocation by rota tion is said to be incomplete when one condyle revolves around the other, com plete when both revolve around a central axis. There may be additional backward or outward displacement. The rotation is said to be outward or inward accord ing to the direction in which the toes turn. Reduction is easy. All knee-dis locations should be kept immobilized for several weeks after reduction.