Arthritic shoulder. X-ray of a frontal view of the right shoulder of a patient with periarthritis. The humerus (upper arm bone) is at left. It articulates with the scapula (shoulder blade, upper centre) and clavicle (collar bone, top) to form the shoulder joint. Periarthritis, or frozen shoulder, is inflammation of the tissues surrounding the shoulder joint. Also seen is calcification (hardening, white) of tissue between the clavicle and the head of the humerus. Periarthritis causes pain and loss of movement. It may be associated with other types of arthritis, or develop after dislocation or fracture. Treatment is with physiotherapy and anti- inflammatory drugs.