Stages of osteonecrosis of humeral head. Stage I changes are invisible on plain radiographs, and they are not discernible on gross examination. Stage II is marked by sclerotic changes and evidence of bone remodeling, but shape and sphericity of humeral head are maintained. Stage III is differentiated from stage II by presence of subchondral bone collapse or fracture, resulting in loss of humeral head sphericity. In stage IV, humeral head has area of collapsed articular surface; fragment may become displaced intraarticularly. In stage V, there are osteoarthritic changes in the glenoid fossa.