Osteonecrosis of the humeral head (ONHH), also known as Hass disease, is considered the second commonest location for osteonecrosis (following the hip).
It generally develops in the subchondral region. In some patients, osteonecrosis can lead to collapse of the necrotic subchondral bone, development of an irregular joint surface, and subsequent joint degeneration.
The general risk factors for osteonecrosis, in general, apply to humeral head osteonecrosis. Corticosteroid use has been recognized as a dominant causative association .
While many of the general radiographic features for osteonecrosis may be present with ONHH, the presence of crescent sign can be the classic diagnostic feature in the correct clinical context .