MRI of joints in sports medicine requires consideration of multiple technical factors. A dedicated extremity coil appropriate for the particular joint is desired. The type of abnormality clinically suspected, the magnet field strength, the desired anatomic coverage, and the presence of postsurgical change or indwelling hardware are important considerations. In the majority of cases of stress response as well as stress fracture, there is no abnormality on plain film radiographs . Occasionally subtle periosteal reaction may be seen, but often there is no detectable cortical fracture line. Therefore, a heightened awareness of the signs, symptoms, and presentations of stress fractures must be maintained in order to avoid significant delays in diagnosis that can significantly alter the recovery time and prognosis of the injury. Normal plain films cannot exclude a stress reaction or stress fracture.
Bone scintigraphy is a highly sensitive imaging modality, but lacks specificity in small joints such as the ankle and foot. A triple-phase bone scan is typically performed, consisting of an immediate postinjection blood flow phase, a blood pool phase, and delayed 3 to 6 hour imaging. Activity is demonstrated in areas of new bone formation at sites of healing stress fractures where there is osteo-blastic activity occurring. Stress fractures may be asymptomatic and found incidentally on bone scintigraphy or plain films .
CT is less commonly used for stress fracture imaging, but has been described as useful in the diagnosis of the uncommon longitudinal stress fractures of the tibia .
MRI has proven to be extremely useful in the diagnosis of stress reaction and stress fracture, and has a high degree of sensitivity and a higher degree of specificity relative to bone scintigraphy in terms of the site of injury [7,8,14,16-20]. MRI typically shows periosteal edema and bone marrow edema without a visible fracture line in cases of stress reaction without fracture. There may be a variable degree of surrounding soft-tissue edema. Enhancement of the marrow and surrounding soft tissues may be seen after contrast administration, mimicking other disease such as infection or tumor. Similar findings with the additional finding of a low signal cortical fracture line are seen with stress fractures .
A discussion of the various locations where stress-related injuries tend to occur follows, in a distal to proximal order (Table 1).
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