Arthritic shoulder. Coloured X-ray of the shoulder of a 68 year old patient with osteoarthritis. The humerus (upper arm bone) is at left. It articulates with the scapula (shoulder blade, centre right) and clavicle (collar bone, top) to form the shoulder joint. In a healthy shoulder there would be a clear gap between the head of the humerus and the scapula. Osteoarthritis is a degenerative disease, caused by mechanical wear and tear, that leads to the loss of the protective cartilage between joints. This causes pain and stiffness. Treatment is with anti-inflammatory drugs and physiotherapy. In severe cases the joint may be surgically replaced.