Osteochondritis dissecans has been shown to heal with protective weight bearing alone, if there is no loose body in the joint. Magnetic resonance imaging can accurately predict the presence and extent of chondral fragments, and it appears that a magnetic resonance staging classification has been developed that allows preoperative staging of lesions of the talus and the knee. In a large study of hip dislocations, the most important predeterminant of poor clinical outcome was the presence of avascular necrosis. In addition to stigmata of rheumatoid arthritis, recognizable in 90% of 107 femoral heads in rheumatoid arthritis patients, 29 heads (28%) had intracapital trabecular fractures that were either the sole feature or a very important feature of the histopathology. In systemic lupus erythematosus patients the mean maximal daily dose of prednisone was significantly greater in patients with osteonecrosis than in those without bony complications. A novel canine model allowing investigations into the pharmacologic regulation of circulation in bone is discussed along with the first demonstration in humans of a pharmacologically produced decrease in bone marrow pressure. In spontaneous osteonecrosis of the knee, patients with magnetic resonance abnormalities on T2-weighted images have a poor clinical outcome. Magnetic resonance imaging of the hip can provide images of equal resolution in any plane, which is helpful in evaluating the extent and location of femoral head involvement. A large study revealed that total joint replacement should be done judiciously in osteonecrosis, because there is a 37% overall failure rate as compared to 10% failure rate in total hip replacements done for other causes.(ABSTRACT TRUNCATED AT 250 WORDS)