Osteonecrosis or avascular necrosis maybe caused by a number of primary insults however, the final common pathway is thought to be interrupted vascular supply with death of cellular elements. Primary etiologies may include; 1) trauma with interruption of arteries, 2) embolic disease as seen in sickle cell or Caisson disease, 3) inflammatory narrowing as in collagen vascular disease or radiation, 4) cellular accumulation seen in steroid use or glycogen storage disease. Idiopathic disease also exists.

AVN of the hip can present as hip, groin, thigh or knee pain. Radiographs are typically insensitive early in the disease and may present with the appearance of mild DJD although the joint space is typically preserved. Scintigraphy and MR are much more sensitive for early AVN. Ischemia may be detected up to one year prior on scintigraphic imaging as a photopenic defect. Marrow imaging with sulfur colloid is even more sensitive than routine bone scans. Subsequent findings may include the "doughnut sign"; a rim of increased radiotracer uptake surrounding a photopenic defect, or late findings of uniform increased activity throughout, that represents capillary revascularization and new bone formation.