Imaging of the Wrist and Hand

, Royal Victoria Hospital, McGill University, Montrèal, Canada.

Disclosures

Medscape General Medicine. 1999;1(1) 

In This Article

Magnetic Resonance Imaging (MRI)

MRI is a form of nonionizing radiation that allows imaging of bone marrow, soft tissues (including cartilage, ligaments, and tendons) and neurovascular structures in three planes (Fig. 18). Images are generated based upon the net magnetization resulting from the spin of protons within a magnetic field.

Figure 18. Transaxial MRI images, gradient echo sequence. The normal anatomy of the wrist is shown. (a) The distal radius and ulna are identified. Lister's tubercle is identified along the dorsum of the wrist. (b) At the level of the carpal tunnel, the hamate, capitate, trapezoid, and trapezium are identified (from left to right). The flexor tendons and transverse carpal ligament are seen ventrally. The extensor tendons are identified along the dorsum of the wrist.

Several patient factors should be considered prior to MR imaging, including patient size/weight, the patient's propensity for claustrophobia, and the presence of metallic objects within the patient. As allergies to MR contrast agents are rare, patient allergies play a relatively minor role in pre-MR screening as compared with CT. Technical considerations that weigh on image quality include the strength of the magnet, the body part to be imaged, the position of the part of interest within the magnetic field, patient motion, and the coils available for imaging.

It is MRI's unique ability to image bone marrow that has revolutionized fracture detection. In most cases where plain radiographs are unrevealing, MRI is the subsequent examination, replacing CT and/or bone scintigraphy in the role of fracture detection (Fig. 19). MRI has improved sensitivity as compared to both CT and bone scintigraphy, and it has much improved specificity in comparison to bone scintigraphy.[19,20,21,22] MRI's utility in the detection of scaphoid wrist fractures, and hence in the reduction of associated complications of the scaphoid fracture, cannot be underestimated (Fig. 20).

Figure 19. Coronal MRI. (a)T1- and (b) T2-weighted spin echo images. A linear band of low- and high-signal intensity, respectively, is identified through the scaphoid waist indicative of a fracture. Radial-sided soft tissue edema is also evident.
Figure 20. Posteroanterior view of the left wrist. Sclerotic margins at the scaphoid waist fracture indicate the presence of a nonunion. Osteophytosis, cartilage loss, and remodeling are seen at the radial styloid-scaphoid articulation, indicating osteoarthritis. Cartilage loss at the scaphocapitate and capitolunate joints also indicate degenerative change. The constellation of findings is consistent with scapholunate advanced collapse (SLAC), likely secondary to a chronic scaphoid waist fracture.

Similarly, MRI plays a significant role in the detection of radiographically occult avascular necrosis (AVN).[23, 24] By allowing early detection of AVN, treatment can be instituted in early disease stages, potentially resulting in a more favorable outcome (Fig. 21). MRI as a marrow imaging tool may also be helpful in determining the etiology of repetitive wrist trauma, as in cases of ulnar impaction.[25]

Figure 21. (a) Coronal and (b) sagittal MRI images, T1-weighted spin echo sequence. Small areas of low-signal intensity are seen within the lunate bone consistent with Kienböck's disease. There is no evidence for collapse of the lunate. Plain radiographs of the wrist (not shown) were normal.

Although unchallenged as a tool for imaging soft tissue tumors, MRI has not yet been widely accepted as the modality of choice for evaluation of the ligaments and TFC of the wrist. Whereas MRI's marrow and nonligamentous soft tissue imaging capabilities rely on standard sequences and applications of the MRI scanner, this is not the case for ligament imaging. High field strength and high-resolution MR images obtained with dedicated extremity coils are required to derive detailed information about small anatomic structures like the scapholunate ligament. Although MR arthrography has alleviated some of the difficulty in visualization of the wrist ligaments, it is invasive, time-consuming, and costly. Thus, in most practices wrist arthrography remains the study of choice for evaluation of the ligaments and TFC.[26,27,28,29]

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