#Arthritis deformans# affects the knee more frequently than any of the other large joints. The changes related to the synovial membrane here attain their maximum development, and may assume the form of hydrops with or without fibrinous bodies, or of overgrowth of the synovial fringes and the formation of pedunculated loose bodies. It is suggested that these synovial changes follow upon repeated sprains or upon a previous pyogenic infection of the joint. The effusion and stretching of the ligaments that follow upon a sprain are incompletely recovered from; the synovial membrane becomes puckered, the quadriceps atrophies and no longer puts the ligamentum mucosum on the stretch; and the infra-patellar pad of fat, not undergoing the normal compression during extension, is readily nipped between the femur and tibia. Each nipping implies a fresh sprain, with return of the effusion, and so a vicious circle is set up which terminates in what has been called a _villous arthritis_, with fringes and loose bodies; in time, the articular cartilage at the line of the synovial reflection undergoes fibrillation and conversion into connective tissue, and the process spreading to the articular surfaces, the picture of a rheumatoid arthritis is complete. Fibrillation of the cartilage imparts a feeling of roughness when the joint is grasped during flexion and extension, and lipping of the margins of the trochlear surface of the femur may be felt when the joint is flexed; it is also readily seen in skiagrams. When a portion of the "lipping" is broken off, it may give rise to a loose body. In advanced cases with destruction of the cartilages, there may be movement from side to side, with grating of the articular surfaces.
In the early stages, treatment consists in limiting the movements of extension by means of a splint provided with a hinge that locks at thirty degrees from full extension and vigorous massage of the quadriceps. In the dry, creaking forms of arthritis, the symptoms are relieved by introducing liquid vaseline into the joint. When the symptoms are due to the presence of fringes and loose bodies, these may be removed by operation. When the disease is of a severe type, and is confined to one knee, the question of excising the joint may be considered.