Knee arthritis causes pain and decreased mobility of the knee joint. The cartilage lining is thinner than normal or completely absent. In the arthritic knee, there is an absent joint space that shows on X-ray. In the normal knee, there is a normal joint space. The capsule of the arthritic knee is swollen. The degree of cartilage damage and inflammation varies with the type and stage of arthritis.
Patellofemoral arthritis is an inflammatory condition characterized by loss of the smooth cartilage between the kneecap (patella) and the underlying femoral (thigh) bone in the knee joint. When the articular cartilage wears out, the underlying bones rub against each other, causing pain, swelling, stiffness, and restricted movement.