Frontal X-ray of a 54-year-old male patient with pain in the left groin. The X-ray shows narrowing of the left hip joint space (centre right) and osteonecrosis of the left femoral head. 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 most commonly affects the bones of the hips, knees and face. It can cause the bone and joint to collapse, and hip joints may need replacing or resurfacing.