One of the common indications for MRI of the hip is to are the standard radiographs performed for the assessment determine the presence of ischemic necrosis. This is bone of hip joint abnormalities (26). The presence of osteoarthri death produced by a compromised blood supply. It also has tis, bone tumors, and soft-tissue calcifications can be assessed been called avascular necrosis, osteonecrosis, or aseptic necrosis. Predisposing factors that should raise the physician’s index of suspicion include corticosteroid therapy, alcoholism, known hip trauma, chronic pancreatitis, Gaucher’s disease, sickle cell disease, exposure to hypobaric conditions, subcapital fractures, childhood septic arthritis or osteomyelitis of the hip, and congenital hip dislocation (27). If undetected early, the disease can progress and finally undergo irreversible collapse of the femoral head. MRI has been demonstrated to be even more sensitive and specific than bone scintigraphy for the early diagnosis of ischemic necrosis of the femoral head (28–31).
On T1-weighted MRI, the foci of ischemic necrosis of the femoral head appear as homogeneous or heterogeneous well-delimited or diffuse areas of decreased signal intensity in the shape of rings, bands, wedges, or crescents, or in an irregular configuration (Fig. 6-18A–C) (32–33). The low signal intensity is caused by death of marrow fat and replacement of the marrow by a fibrous connective tissue. Some cases show a lower signal band surrounding the lesion, and this has been attributed to healing sclerotic bone at the interface between normal and necrotic bone. On T2-weighted images, many cases show a double-line sign with a high–signal-intensity zone just inside of a low–signal-intensity margin. This is thought to be produced by granulation tissue surrounded by sclerotic bone (31–33).
FIGURE 6-18. A: Frontal radiograph on patient with advanced left hip AVN. There is sclerosis to the femoral head and collapse (arrow) to the articular surface. Bilateral ischemic necrosis of the femoral head in a different patient. B: coronal T1-weighted, serpiginous areas of decreased signal intensity are well demarcated within the subchondral marrow. C: coronal T2-weighted fat suppressed images. There is edema within the right femoral head (arrowheads) on the right femoral head. The left femoral heads demonstrates a serpiginous area of increased signal intensity. These findings are characteristic of AVN.
Source: Physical Medicine and Rehabilitation – Principles and Practice
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