A total shoulder arthroplasty, or joint replacement, is sometimes performed to repair a fracture of the proximal (or upper third of the) humerus, the large bone of the upper arm. 'One of the problems with the proximal, or ball, part of the shoulder joint,' says Dr. Garg, 'is that its blood supply can be somewhat precarious, and if there's been a fracture with numerous fragments, some of those fragments don't have a good supply and may not heal, or the bone actually may die there.' More often, a shoulder arthroplasty is done because of arthritic change. Someone may have completely worn out the articular cartilage in their shoulder joint, either as a result of osteoarthritis - in which case it's usually someone in their 60s or 70s -
