X-ray of the knees of a 55 year old patient with osteoarthritis in both knees. The narrowing of the space between the femur (thigh one, top) and tibia (shin bone, bottom) indicates osteoarthritis. Osteoarthritis is a degenerative joint disease that results from the breakdown of joint cartilage and the underlying bone, resulting in joint swelling, pain and a decreased range of motion. Treatment is with the surgical replacement of the joint.