Plain radiography is the standard imaging technique. It provides the vast majority of information needed in many hand and wrist disorders.
Advanced imaging is necessary when disorders cannot be adequately assessed through routine measures.
A bone scan is a minimally invasive technique that provides information about blood flow, soft tissue elements and bone pathology. Anatomic resolution is poor, yet bone scanning is an important adjunct to other imaging modalities. Bone scanning is useful especially when the diagnosis is enigmatic.
Arteriography is a minimally invasive technique to accurately visualize arterial anatomy and integrity and may be necessary when considering vascular surgery or to view the vascularity of musculoskeletal lesions.
Ultrasound is a noninvasive modality for viewing and differentiating masses within the musculoskeletal system, especially between solid and cystic masses. Ultrasound can provide a dynamic account of tendon excursion as well, and look for tendon injury.
Computed Tomography (CT) is a noninvasive modality, but exposes patients to ionizing radiation. Benefits include the ability to observe occult fractures within the carpus, identify displacement of fracture fragments, and evaluate for bone healing and nonunion. CT is especially useful for looking at the distal radioulnar joint for subluxation or dislocation.
Magnetic Resonance Imaging (MRI) is a noninvasive imaging technique that has become the gold standard in viewing and differentiating soft tissue lesions, identifying lesions of the carpal ligaments, triangular fibrocartilage, and occult fractures of the hand and wrist. Flexor tendon injuries and tenosynovitis is easily identified. MRI is contraindicated in patients with pacemakers and cochlear implants.
The diagnosis of upper extremity disorders relies on information obtained in the history, physical examination, and views of the region acquired through one or more imaging techniques. Plain radiography provides adequate visualization of most problems and, for that reason, is a standard part of the initial evaluation. Excellent depiction of fractures, fracture alignment, fracture healing site, dislocation, soft tissue calcification, foreign bodies, and bony detail can be obtained by this readily available, cost-effective, and noninvasive means. In certain cases, however, the problem cannot be properly assessed by routine measures; thus, other imaging modalities are needed to provide further diagnostic information. In this chapter, radiography and advanced imaging techniques are discussed in relation to the diagnosis of hand and wrist disorders.
Routine studies of the hand consist of posteroanterior (PA), lateral, and oblique views, which are evaluated for bone density, bony lesions, fractures and dislocations, integrity of the articular surfaces and joint spaces, and irregularities of the soft tissue ( Fig. 13-1 ).
Bone density, which is evaluated grossly, may be normal, less than normal (osteopenia), or greater than normal (osteosclerosis). Osteopenia is most often encountered in the elderly and is known as senile osteoporosis when associated with advanced age. Osteosclerosis occurs in conditions such as avascular necrosis (AVN) ( Fig. 13-2 ), fracture healing, and metabolic bone disease. Plain films may reveal discrete or diffuse bone lesions, including primary or metastatic bone tumors, infection, and metabolic bone disease ( Fig. 13-3 ). The cortical integrity is carefully inspected for evidence of acute fracture ( Fig. 13-4 ) and the joint alignment evaluated for subluxation or dislocation. Abnormalities of the articular surface and cartilage joint space also are documented. Narrowing of the cartilage space may indicate arthritis, resulting from degeneration, inflammation, infection, or trauma ( Figs. 13-5 and 13-6 ). Finally, the soft tissue shadows are evaluated for irregularities. Any evidence of calcification ( Fig. 13-7 ), foreign bodies ( Fig. 13-8 , online), or soft tissue masses must be correlated with the clinical findings.
If the history and physical examination indicate a localized problem, a coned-down view of the area can be obtained. This magnified spot film focuses on a specific area of the wrist, which is especially useful for isolated disease of the carpal bones because fractures and abnormalities in this region often cannot be seen on plain views ( Fig. 13-9 , online). Special positioning and maneuvers also are used to allow more complete visualization of a possible pathologic condition. For example, stress views may demonstrate joint malalignments that are not evident on routine films. Tears of the ulnar collateral ligament of the thumb metacarpophalangeal (MCP) joint are a case in point because these can become apparent by applying a force to this joint in radial deviation ( Fig. 13-10 ). A special maneuver is often needed to demonstrate damage to the scapholunate ligament complex. This complex is important in stabilizing the scaphoid and preventing rotatory subluxation. When it is injured, the scapholunate interval may appear completely normal on a routine view, but it widens when a compression load is applied by clenching the fist in supination ( Fig. 13-11 ). Recently, a modified clenched-fist view, called the “clenched-pencil” view, was described. This view allows the appropriate amount of pronation of the wrist to view the scapholunate interval most favorably. Special views, such as those of the trapezial ridge ( Fig. 13-12 ) and hook of the hamate ( Fig. 13-13 ), also are useful in demonstrating the bony anatomy of the carpal tunnel and certain fractures.
Advanced Imaging Techniques
When a diagnosis cannot be made on the basis of the routine clinical examination and plain radiographs, more advanced imaging techniques can be used to visualize the bone and soft tissue anatomy more completely. The decision to use another technique must consider the invasiveness and cost of the procedure ( Table 13-1 , online) as well as its specificity.
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Plain tomography is capable of visualizing healing bone and fracture nonunion better than routine radiographs, especially in cases involving the scaphoid and hook of the hamate. This examination is noninvasive and relatively inexpensive. Computed tomography has largely replaced plain tomography in most centers. CT is more clinically useful than conventional tomography because it can obtain multiple contiguous sections with high resolution in a short time, multiplanar image reconstruction is possible, and additional information about adjacent soft tissues can be obtained. 3D reconstructions are now also available to help in planning surgery. CT remains the best modality for demonstrating bony architecture.
CT is useful in evaluating complex fractures and bony lesions, providing superior detail of cortical invasion, marrow abnormalities, and matrix calcification. It is also an excellent means of depicting subluxations and dislocations of the distal radioulnar joint. In patients with metallic hardware, significant scatter often overlays the image of the bony segment. Image techniques can be manipulated to minimize this beam-hardening artifact to fine-tune visualization of the bony anatomy. The advantage of CT over conventional radiography lies in its ability to obtain transaxial images and provide excellent contrast resolution for evaluating soft tissues. This modality is also noninvasive, unless used in conjunction with contrast agents. CT exposes patients to potentially harmful ionizing radiation. With the advent of fast CT scanners, availability has led to increased radiation doses to patients.
Bone scintigraphy involves the intravenous (IV) injection of 99m Tc-labeled monodiphosphonate (MDP), which is preferentially taken up by bone. Flow images are generated after 60 seconds, and a nuclear medicine angiogram is obtained. Delayed images are generated after 3 hours. Areas of abnormal blood flow and bone turnover can be detected on the scan, making it useful in the evaluation of infection, AVN of the lunate, tumors, and reflex sympathetic dystrophy. It also is used to screen patients who have unexplained wrist pain ( Fig. 13-14 ).
The examination is minimally invasive and moderately expensive. The poor anatomic resolution of the scan is its primary drawback. The test also is nonspecific, making it impossible to distinguish various processes that can cause increased uptake. The results must be carefully correlated with the clinical findings to be properly interpreted. Today, MRI has largely replaced scintigraphy in most centers in musculoskeletal imaging.
Arteriography is the most specific means of evaluating vascular anatomy and pathology; it is used to evaluate aneurysms, arteriovenous malformations, tumors of vascular origin, traumatic vessel injuries, and solid tumor vascularity ( Fig. 13-15 ). The examination is performed by threading a catheter into the brachial artery using a femoral approach, injecting contrast material, and then taking multiple radiographs. The procedure is often painful, even with the use of new nonionic contrast material. Complications include bleeding hematoma, pseudoaneurysm formation, dissection, and thrombosis. The contrast medium may cause arterial spasm, although this can be controlled with the use of vasodilators. Anaphylaxis is another potential complication when iodinated contrast material is used, but severe episodes are rare, occurring in only 1 of 40,000 cases.
In the diagnosis of bone and soft tissue tumors, conventional angiography has largely been replaced with MRI and magnetic resonance angiography (MRA) to avoid potential complications.
Arthrography is used to evaluate the integrity of the carpal ligaments and triangular fibrocartilage (TFC) ( Fig. 13-16 , online). The examination involves injecting dye into the radiocarpal, radioulnar, and midcarpal compartments, so it must be performed carefully. The injection of contrast material into the joint can highlight intra-articular soft tissue structures such as ligaments and fibrocartilaginous structures. Communication of dye between the compartments of the wrist can be caused by a clinically unimportant perforation and does not necessarily indicate pathology. Thus, the test results must be correlated with the clinical examination and interpreted with a great deal of caution. The examination is invasive but can be administered with minimal discomfort to the patient.
The role of arthrography had declined because of the excellent visualization of intra-articular structures by MRI. Arthrography has also been found to be only 60% accurate in detecting tears in the triangular fibrocartilage complex (TFCC), scapholunate ligament, or lunotriquetral ligament. Arthrography is currently used as a complement to MRI and CT to enhance the diagnostic accuracy.
Continuous radiographic imaging has many applications such as arthrography, tenography, bursography, arteriography, and percutaneous bone and soft tissue biopsy. Evaluation of the wrist in motion is a useful method for detecting the rigidity of a freshly fixed fracture or for dynamic carpal instability. This noninvasive and inexpensive technique is the diagnostic imaging procedure of choice for determining and documenting the presence of dynamic rotatory subluxation of the scaphoid. The role of MRI in this capacity is evolving but remains problematic. Dynamic MRI is a newer technique that may yield more comprehensive clinically relevant information with regard to wrist kinematics than conventional MRI.
Magnetic Resonance Imaging
MRI visualizes tissue by applying a strong magnetic field with radiofrequency pulses to record differences in tissue signal intensity. A variety of magnet strengths are available from 0.2 to 3 T, with higher strengths providing greater contrast resolution. MRI provides high resolution and high-contrast tissue segmented information about the integrity of joint and soft tissue structures. It also is completely noninvasive, involves no ionizing radiation, and is able to obtain images through cast and fiberglass materials that limit the resolution of conventional radiography and CT. Among its minor drawbacks are its contraindications in patients with pacemakers, cochlear implants, or ferromagnetic aneurysm clips. Implanted metallic objects create “holes” and distort the images of tissues hoped to be visualized. In addition, the examination is performed with the patient lying in a narrow cylinder within the bore of a magnet, a closed space that may cause some individuals to become claustrophobic. In the event of such anxiety, IV benzodiazepam may be administered to the patient, provided that the patient can be monitored properly during sedation. Open MRIs have evolved and are advantageous in this setting. The diagnostic accuracy of low-field open scanners has been found to be comparable to that of high-field scanners. Evaluating a suggested pathology with MRI involves the use of multiple sequences, including T1, T2, short tau inversion recovery (STIR), and spin echo; for this reason, close communication between the orthopedist and radiologist is essential.
MRI is of great value in defining soft tissue abnormalities ( Figs. 13-17 to 13-19 , all online). In the evaluation of tumors, it cannot provide a specific diagnosis, but it can define the size of the lesion and the extent of involvement of marrow and neurovascular structures ( Fig. 13-20 , online). Other soft tissue abnormalities diagnosed more easily by MRI include ganglions, ligament tears, and cartilage abnormalities ( Fig. 13-21 ). Dorsal wrist pain can be attributed to hypertrophy of the dorsal capsule as well as ganglions that may be occult and not palpable. Patients with dorsal wrist pain of unknown origin are therefore candidates for MRI evaluation. MRI is especially helpful in diagnosing tears of the scapholunate and lunotriquetral ligaments, particularly when dissociation of the scapholunate is not evident on plain films. Excellent depiction of the TFC can be achieved with MRI, but the image must be interpreted carefully; thinning of the disk occurs in many patients, but a tear of this structure is not diagnosed unless an avulsion from the ulnar or radial insertion can be observed.
MRA is another tool that can easily demonstrate vascular abnormalities. MRA provides detailed information about the anatomy of the small vessels that constitute the carpal arches. MRA is noninvasive because it does not require the use of IV contrast material ( Figs. 13-22 and 13-23 , both online). Rather, it relies on the property of blood flow, and special pulsed sequences are used to enhance the fluid within the vessels.