Osteonecrosis of the hips. Magnetic resonance imaging MRI sequence showing osteonecrosis of the hips in a 45_year_old man. The sequence shows a coronal view of the hip region, moving through the hips from back to front, and then back again. The backbone, genitals, and leg muscle grey and surface fat white are also seen. The necrotic bone in the femoral heads is seen as grey areas at the tips of the bones in the first pass, and then in orange in the paused shot in the reverse pass. Also known as avascular necrosis or aseptic necrosis, this condition is caused by poor blood supply to the affected area and the bone marrow. It can cause the bone and joint to collapse, and hip joints may need replacing or resurfacing. In this case, a total hip replacement will be needed in the next few years. For the same sequence with the necrosis not highlighted, see clip K003/1303.