(From because by this articulation the body is bent towards the earth). The knee; also the patella, knee pan. The knee is the articulation of the thigh and leg bone; as a gin-glymus it admits of only flexion and extension, except in its bent state, when it will allow of a small rotation by the relaxation of the ligaments. This joint is made up of the femur, patella, and tibia; for the fibula does not reach it. The patella in extension is drawn up, in flexion pulled down. Under the ligament of the patella is a sac containing mucus, resembling the synovia. Its strength, as of all joints of the same kind, is on the side. The capsular ligament is large, and admits of the collection of a fluid within it when the swelling appears above and on each side the patella, but chiefly above, on account of the ligaments being thinner. What is called the synovial gland Dr. Hunter concludes is merely fat, like all the glands of a similar kind; and the real synovia is, he thinks, secreted by the vessels of the vascular membrane which covers the cartilages. Besides the capsular ligament, there are two others covering the posterior parts of the condyles of the femur, and fixed into the head of the tibia, between its two cavities; these ligaments are stretched when the leg is extended, and relaxed when the leg is bent, allowing at this time a little lateral motion. Between the tibia and the femur are two semilunar cartilages, thick on their external edges, and thin in their centre; and tied to the tubercle by their horns: they alter their figure according to the situation of the bones, to make the shape of one correspond to that of the other.

It sometimes happens that one or two pieces of cartilage, or bone covered by cartilage, are found loose in the cavity of this joint. Some of these are as large as common garden beans: they are generally flat, oblong, having their edges rounded. Mr. Cruickshank formerly considered them as belonging to the patella; and that, like the ossa triquetra in the skull, they were owing to distinct points of ossification: but having found one entirely cartilaginous, and another bony one covered by cartilage, formed on the lower end of the femur, he was convinced of his mistake. In the last mentioned case, Mr. Cruickshank observes that there was a cavity in the lower end of the femur, corresponding to the loose bone, showing a former connection; though, as both surfaces were nearly smooth, its manner was not evident. He supposes that during their growth these cartilages and bones are connected to the neighbouring parts by vessels; and that, when either their determined bulk is completed, or their size too large for the easy motion of the joint, they become loose. When this happens, the synovia, from the irritation, is secreted in greater quantity; the capsular ligament is distended, a degree of stiffness takes place in the motion of the joint, with more or less of external inflammation. The fluid underneath is distinctly felt; and the loose bit of cartilage rises frequently above the condyles of the femur, on the out or inside of the knee, and may be taken between the thumb and finger through the integuments. When the patient hath walked much, the synovia is sensibly increased; and, on remaining quiet for two or three days, is as sensibly diminished. The symptoms are sometimes so mild as not to need an operation; but it is often the only expedient for relief. Mr. J. Hunter recommends removing them by incision; but thinks the particular spot where the operation is to be performed, as well as the manner of operating, deserve the greatest attention. There is a part of the ligament which receives the basis of the patella during the extension of the leg, and rather resembles cellular membrane than capsular ligament, lying under the lower extremities of the vasti and crureus muscles, before they are inserted into the patella. Mr. Hunter proposes to lay hold of the cartilage or bone, and cut upon them at this place: the incision, he thinks, should be no larger than just to allow of their being easily-thrust out. A stitch or two is then to be passed through the divided integuments, but not into the cavity of the joint, and the lips of the wound by these means brought together. If they penetrated the joint, instead of uniting the parts, they would act as seatons, and produce inflammation: for by a seton introduced into the tunica vaginalis testis we often obtain a radical cure of the hydrocele. The aim of the surgeon is, if possible, to heal the wound by the first intention; and a piece of sticking plaster, with a proper bandage, and position of the joint, may make stitches unnecessary. Mr. Hunter recollects six or seven cases in which these cartilages were removed by excision, though not exactly in the manner recommended; all of these succeeded except one, where the operation was attended with great inflammation, and followed by an anchylosis of the joint. Other instances of failure have occurred; but there are constitutions where any wound, particularly a penetrating one into the cavity of the joint of the knee, will be attended with danger. The circumstances to be avoided are too much exposing the cavity of the joint; lacerating or bruising of the capsular ligament; not properly closing the orifice in the integuments; or employing a blunt or dirty instrument in dividing them. Each may produce inflammation, and render the operation dangerous; but in tolerably sound constitutions, when performed with the necessary precautions, it is generally safe: when, however, the cavity of the joint is inflamed, the danger is very great. Ligaments and cartilages have fewer vessels than most other parts: they inflame, and suppurate, if exposed to irritation, with greater difficulty; the joint anchyloses, and is destroyed, or the patient sinks under a hectic from absorbed matter, if the limb is not amputated. See Cruickshanks in the Edinburgh Medical Commentaries, vol. iv. p. 342, & c. Hunter's Works. Hay's Observations in Surgery.