Mri

MRI, like nuclear medicine, is sensitive to detecting early marrow changes and early stress reactions. MRI also provides a detailed anatomic evaluation of the regional soft tissues and can be used to quantify the quality of the endosteal and cortical bone.

MRI can be used to evaluate both the appendicular as well as the axial skeleton. MRI provides a comprehensive evaluation of the area in question, providing morphologic as well as functional information. MRI can demonstrate the status of the intramedullary bone, areas of bone edema or turnover, perios-teal reaction, and frank fracture lines (Figs. 5 and 6). The addition of at least one water-sensitive pulse sequence (fat suppression or inversion recovery) should be included in all MRI examinations to evaluate for bone marrow edema (see Figs. 2, 3, 5, and 6). Endosteal marrow edema is one of the earliest signs of stress remodeling and can be seen with MRI [12].

The cross-sectional imaging capabilities and the ability to diagnose subtle marrow changes of MRI can help identify osseous abnormalities in areas not readily visualized with conventional radiography, such as the sacrum and pelvis. Specifically, stress fractures of the sacrum, which often are encountered when a long-distance runner changes the level of activity, can be difficult to discern on routine plain film radiographs. The importance of diagnosing stress fractures of the sacrum is that they can potentially mimic intervertebral disc pathology, which dictates a different course of clinical management [13]. A single large-field-

Bone Fractures Mri Images

Fig. 5. (A) Sagittal fast inversion recovery MRI of the lateral margin of the ankle demonstrating a striking bone marrow edema pattern in the fibula with periosteal reaction consistent with a stress fracture. (B) Sagittal fast spin echo MRI in the same patient demonstrates mild ill-defined endosteum and periosteal new bone formation (arrow).

of-view water-sensitive pulse sequence can be used to provide a global overview of the lower lumbar spine, pelvis, and hips in patients presenting with nonspecific hip, lower- back, or groin pain, and in those in whom a stress fracture is a clinical concern. This "survey image" of the pelvis is especially useful to evaluate patients who have nonlocalizing clinical symptoms.

Another important application of MRI is in diagnosing femoral neck stress fractures. Femoral neck stress fractures can present with symptoms of pain in the groin, hip, or anterior thigh, often mimicking other potential sources of pain such as a labral tear or iliopsoas tendon pathology [14]. Radiographic findings can lag behind clinical symptoms by a period of weeks to months, thus potentially resulting in a delayed diagnosis and completion of the fracture [15]. In addition, if the patient is moderately to severely osteoporotic, the diagnosis of an early, nondisplaced femoral neck fracture on routine anteroposterior and lateral radiographs can be limited. The advantage of MRI in contrast to nuclear medicine scintigraphy is that it can identify bone marrow edema and also can demonstrate the location of the fracture, classifying the fracture as a compression (on the inferior aspect of the neck) or a tension (on the superior aspect of the neck) type, of which the latter is considered to be more unstable [16].

Because MRI is sensitive for diagnosing bone marrow edema, the imaging findings should be interpreted in conjunction with the patient's symptoms. The presence of bone marrow edema can remain long after the initial diagnosis and treatment of a fracture, whereas the cortical bone matures and remodels. It has been demonstrated that the bone marrow edema pattern on MRI may be present for up to approximately 6 months after an initial diagnosis of a femoral neck

Fig. 6. (A) Sagittal fast inversion recovery MRI of the knee demonstrating bone marrow edema pattern concentrated in the proximal posterior margin of the tibia, where there is a frank fracture line posteriorly and periosteal reaction. Sagittal (B) and coronal (C) fast spin echo MRIs in the same patient demonstrate the morphology and detailed anatomy of the area to better advantage; the fracture line and periosteal new bone formation are evident (B and C, arrows).

Fig. 6. (A) Sagittal fast inversion recovery MRI of the knee demonstrating bone marrow edema pattern concentrated in the proximal posterior margin of the tibia, where there is a frank fracture line posteriorly and periosteal reaction. Sagittal (B) and coronal (C) fast spin echo MRIs in the same patient demonstrate the morphology and detailed anatomy of the area to better advantage; the fracture line and periosteal new bone formation are evident (B and C, arrows).

fracture [17]. In addition, asymptomatic bone marrow edema patterns or stress reactions may be present in relatively asymptomatic subjects, such as marathon runners, who are exposed to osseous stresses. The clinical relevance of this finding has been debated. In one study of asymptomatic runners, tibial stress reactions were noted in the mid diaphysis of the tibiae; of note, these areas of activity did not correlate with the incidence of future frank stress fractures [18]. Similarly, bone marrow edema has been demonstrated in the bones of the feet and ankle in runners [19]. The activity of the intramedullary bone as well as the morphology of the bones (endosteal remodeling and cortical thickening) should thus be evaluated in conjunction with the patient's presenting clinical symptoms.

In summary, MRI can provide detailed information regarding the presence of a stress fracture or stress reaction, especially in cases in which the radiographic findings are inconclusive. MRI can provide information regarding the acuity of the abnormality as well as morphologic information about the bone, including periosteal new bone formation, endosteal remodeling, as well as subtle frank cortical fracture lines.

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