DISLOCATIONS AT THE KNEE-JOINT.
The bones that form the knee-joint have been noted on p. 63. It is to be remembered that the joint is formed by the lower articulating processes, or condyles, of the hip-bone, and the surface of the head of the tibia, that between these two there are crescent-shaped plates of fibrous gristle,and that the joint is strengthened by a large number of strong ligaments. Two ligaments----the crucial ligaments-- are within the joint ; the others surround it. The joint is protected in front by the patella or knee-pan, which has a ligament connecting its lower border with the tibia, and is attached by its upper border to the straight muscle that passes down the front of the thigh. The knee-pan glides up and down on the front of the joint. Now there may be dislocation of the pan, or dislocation of the tibia.
Dislocations of the Knee-pan.—The bone may be displaced to one side or other, or up wards, or it may be turned up on one of its edges. None of these occurrences is very fre quent, but of the four forms the displacement outwards is the most common. It is most fre quently due to falling on the inner side of the knee, but may be caused by sudden contraction of the straight muscle attached to the bone, as when a person makes a sudden jump, or a sud den effort to recover himself after a slip.
Signs.—On comparing the affected knee with the opposite side one observes a great difference in shape, and examination with the fingers shows the knee-pan lying over the outer or inner condyle of the thigh-bone. The limb can neither be bent nor straightened, but is fixed in a slightly bent position. The breadth of the knee is increased.
When the bone has been drawn upwards, which is very rare, and cannot occur without tearing its ligament, it is found above the joint, and a hollow is in the place it ought to occupy.
With displacement edgeways a prominent body, which can be grasped by the fingers, is seen standing out under the skin. In this case the limb is immovably fixed in a straight position.
Treatment—For outward or inward dis placement, place the patient in a sitting posture, raise the leg, so that the heel rests on the shoulder of the operator, and push on the knee-cap with the fingers so as to restore it to its place.
Upward displacement requires to be treated as fractured knee-cap.
Displacement edgeways ought not to be treated till it is found which is the upper and which the lower surface of the bone. The upper surface may look outwards and the under surface inwards, or the reverse may be the case, and unless the position is made out the bone might be turned upside down. The best way of coining to a decision is to learn the direction of the dislocating force. If the force came from the outside it would be the upper surface that would look inward. Having found this out, put the patient in the same position as before, raise the heel and push the bone over with the thumbs.
After reduction the limb should be kept at rest in the extended position for some days at least, hot or cold cloths being applied if pain or any signs of inflammation exist. When the person begins to move about it is well to make a thick covering for the knee, which should be worn for several months.
Dislocations of the (Tibia).— Partial dislocations of the tibia to one side or the other with a slight turning of the bone may occur as the result of sudden twists given to the leg— for instance, by the foot being caught in a hole, or by blows on the side of the limb. Complete dislocation backwards or forwards seldom occurs, however, without such destrua tion to the joint and structures in its neighbour hood as to demand special surgical treatment, because such a dislocation requires great force for production.
The Signs of the side displacement are so marked as to be easily observed. The leg and thigh are no longer in the same straight line, the tibia being displaced to one side; there is a bony prominence at one side owing to the new position of the head of the bone; and the joint is greatly increased in breadth.