Luxation is a condition in which the articulating surfaces are disturbed in their relations. It is due to traumatism, and when it occurs, there is generally a rupture of some of the ligaments with laceration of the adjacent soft parts. If the surfaces are restored to their normal position, inflammatory reaction takes place, the capsule and the ligaments heal, and a normal condition supervenes. If restoration has been incomplete or only partial, absorption of the end of the bone occurs, the periosteum undergoes calcification, and a new joint may be formed. Fibrous tissue, cartilage, or bone may, however, form, and bind the joint so closely that no motion is preserved; this condition is called ankylosis.

Hyperemia of the joints is found after injuries, in mild inflammations, and in rheumatic conditions. The synovial membranes are mainly affected. They are pinkish, swollen, and the synovial fluid is both increased in amount and more watery than normal.

Hemorrhage generally follows an injury, but may occur in inflammations and in the course of hemorrhagic diseases. It is called hemarthrosis. If infection does not occur, absorption slowly takes place, leaving the tissues considerably pigmented.

Arthritis, or inflammation of a joint, may be due to an injury or to a hematogenous infection in certain diseases, as scarlet fever, pyemia, or gonorrhea. The synovial membranes are chiefly involved, the cartilages less so and secondarily. If all the structures of the joints are involved, it is a panarthritis. The exudation into the joint may be serous, fibrinous, or purulent, and the after-results depend mainly upon which variety of arthritis existed. If serous, the fluid is generally soon absorbed and the joint returns to a normal condition. If, however, there is a serofibrinous exudation, the process will probably continue longer and adhesions form within the joint. The most serious variety is the purulent. The entire joint is frequently attacked, the synovial membrane swollen and hyperemic, and the surface covered by pus-cells and fibrin. The joint contains a greater or less amount of pus, and the articulating cartilages may be eroded and even necrotic, with involvement of the neighboring bone.

Any of the above varieties may become chronic, and in the serous form a hydrarthrosis, or collection of fluid in the joint, may be present. In the purulent variety, as a result of the destruction of cartilage or bone, the joint may lose all power of motion - ankylosis - from the formation of fibrous and bony adhesions.

Acute articular rheumatism is a condition in which one or more joints are acutely inflamed and painful. This process is generally considered to be the result of infection; staphylococci, gonococci, and other organisms have been recovered from the affected joints. The joints are swollen, red, and painful, and the surfaces are covered more or less by masses of fibrin, some of which may be suspended in the exudate. There are seldom many leukocytes present. As a result of the inflammation, either fibrous or bony ankylosis generally occurs, with more or less subsequent deformity.

Arthritis deformans, or rheumatoid arthritis, is a chronic process occurring, as a rule, in people past middle life. There is a proliferation of cartilage cells, and finally softening, with ulceration of the superficial cells. This gradually extends down to the bone, the surface of which frequently shows Some absorption. At the edge of the joint exostoses may from The ligaments become contracted and fibrous, and ankylosis occurs. As a result of the destruction of bone and formation of connective tissue, all varieties of subluxations (partial dislocation) and deformities occur.

The joints most commonly involved are those of the hip and knee, metacarpo-phalangeal articulations of the hand, and the corresponding ones of the feet.

Senile arthritis resembles very closely the former variety, except that it is more widespread, involving the hip, shoulder, and elbow, and occurs in old people.

Neuropathic arthritis occurs in spinal diseases, particularly posterior sclerosis, syringomyelia, and transverse myelitis. The joints of the lower extremities are more commonly involved. The lesions closely resemble those of arthritis deformans, but there is seldom much pain.

Arthritis uratica, or gout, is a condition in which there are deposits of urates within the joints and the adjacent connective tissues. It generally affects the smaller joints of the hands and feet, particularly the metatarso-phalangeal articulation of the great toe. The joint becomes red, swollen, and very painful; there is a serous effusion into it, and the salts are precipitated from this fluid. These substances may form quite large, chalky deposits. After repeated attacks chronic changes may occur within the joint, such as softening and erosions of the cartilage, hyperplasia of the periosteum, with some ossification. Besides the local conditions, there are constitutional disturbances and also widespread tissue changes, particularly atheroma of the blood-vessels.

Tuberculosis of the joints is most common in childhood, and may be primary or secondary. It occurs most frequently in the hip, knee, and spine, although any joint may be attacked. In the primary form the synovial membranes are first involved. The secondary variety generally results from extension from tuberculosis of the bone.

In the synovial membrane are found extensive soft granulations in which are seen small yellowish or gray tubercles. Caseous degeneration appears early, as a rule, and the joint may be filled with broken-down tissue forming a cold abscess. When the process has extended from the bone, there is marked destruction of tissue around as well as within the joint. The abscess contents may burrow, and emptying upon the surface form a sinus.

Death may result from associated amyloid disease or exhaustion.

If the process subsides, the joint is usually ankylosed in an abnormal position.

Syphilis of the joints is found in children as a congenital lesion. There are thickenings of the ligaments, ulceration of the cartilages, and a purulent exudation. Occasionally gummata may be present. In adults, as a result of acquired syphilis, there may be a serous or sero-fibrinous inflammation of the joint. Gummata sometimes occur, and as a result of degeneration with fibrous formation may cause lesions similar to arthritis deformans.

Tumors

The synovial fringes may show small lipomata and fibromata. These may become separated and lie free within the joint, the so-called "rice bodies," which are small structures originating from the villi of the synovial membrane; are generally quite numerous, thirty or forty being found at times. The joints may be secondarily involved by new-growths in adjacent tissues.