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MD Consult: Books: Goldman: Cecil Medicine: Chapter 279 – IMAGING STUDIES IN THE RHEUMATIC DISEASES

Goldman: Cecil Medicine, 23rd ed.

Copyright © 2007 Saunders, An Imprint of Elsevier

Chapter 279 – IMAGING STUDIES IN THE RHEUMATIC DISEASES

 

Lynne S. Steinbach

 

Imaging in the rheumatic diseases is essential to diagnosis and assessment of the progression of arthropathy. The mainstay for imaging has always been the radiograph. This continues to be the case, because radiographs provide a relatively low-cost baseline evaluation of the bone, joint, and soft tissue. Frequently, the information provided is adequate for diagnosis and treatment. Other imaging modalities, such as magnetic resonance imaging (MRI), computed tomography (CT), ultrasonography, and bone scintigraphy, can aid in characterization and follow-up of rheumatic disease. This chapter discusses the various imaging options for evaluation of rheumatic disease and describes their capabilities and appropriate use.

RADIOGRAPHY

 

Radiography uses an x-ray source that emits radiation, which penetrates the body to produce the image on a photographic plate. An x-ray generator, image detector, and image processor are needed. The radiology technician who obtains the images must be knowledgeable about the equipment and patient positioning in order to obtain adequate radiographs. The physician who reads the radiograph is responsible for the quality of the study.

The radiographic image represents a map of radiation attenuation through various tissues along the course of the x-ray beam. A white structure such as bone attenuates more radiation than a darker structure such as cartilage, muscle, or joint effusion. An analog detector with a film cassette has been used to image the body for more than a century.

Digital radiography is being increasingly used for imaging. It employs a photostimulated phosphor imaging plate and an image reader–writer that processes the latent image information. When the plate absorbs x-rays, the energy is converted to light energy by fluorescence, with the intensity of light being proportional to the energy absorbed by the phosphor. The stimulated light is used to create a digital image. This is transferred to x-ray film or to a picture archiving system (PACS) that is utilized for viewing by the clinician. Digital images have advantages over conventional radiography in that they can be manipulated by the technologist or by the clinician at the PACS station for contrast and brightness as well as window width and level. Magnification and quantification are also possible. The images can be easily stored and retrieved from a server.

The radiograph is the initial imaging technique used for evaluation of arthropathy. Radiographs are affordable, easily available and render images of the joint with high spatial resolution. Frequently, a radiograph is all that is needed to assess joint damage. Radiographs demonstrate joint changes with high resolution down to approximately 0.05 mm. No other imaging study is able to accomplish this degree of spatial resolution. The radiograph can provide detailed evaluation of osseous cortex. Features such as joint space narrowing, erosion, subluxation, calcification, new bone formation, subchondral cyst formation, subchondral sclerosis, and soft tissue swelling can be evaluated on radiographs ( Fig. 279-1 ).

 

 

FIGURE 279-1  Rheumatoid arthritis is demonstrated on a posteroanterior radiograph of a hand. Findings include joint space narrowing at the radiocarpal and metacarpophalangeal (MCP) joints, with subluxation of the MCP joints and the interphalangeal joint of the thumb, as well as erosions of the metacarpal heads and proximal interphalangeal (PIP) joints.

Radiographs should be obtained with at least two views of the involved bone at 90-degree angles to each other to detect and characterize abnormalities such as erosion, effusion, soft tissue swelling, subluxation, dislocation, and fracture. Standard views usually consist of a frontal and a lateral view, but occasionally oblique and special views are needed, particularly when assessing the elbow, wrist, fingers, ankle, foot, toes, pelvis, or sacroiliac joints. Weight-bearing views of joints may be of value for assessing joint space narrowing, particularly in the knee. Although there is no universal consensus on routine views for the various joints, recommended screening views are listed in Table 279-1 .
TABLE 279-1   — ROUTINE RADIOGRAPHIC SCREENING VIEWS OF THE SKELETON

UPPER EXTREMITY
Fingers PA, lateral (separate fingers)
Hand PA, oblique, lateral
Wrist PA, lateral (both with neutral positioning); ballcatcher oblique view is useful for inflammatory arthritis
Forearm AP, lateral
Elbow AP (supinated), lateral (90° flexed), oblique as needed
Humerus AP, lateral
Glenohumeral joint AP internal and external rotation (axillary, Grashey, or transthoracic view)
Acromioclavicular joint AP, 15 degrees cephalad AP (bilateral weight-holding if dislocation)
Sternum AP, oblique AP (also Hobbs view or lordotic view)
LOWER EXTREMITY
Hip AP internal rotation, frog-leg lateral (or cross-table)
Femur AP, lateral
Knee, arthritis PA flexed and AP weight-bearing views, lateral
Knee, patellofemoral joint Merchant view (45° flexion)
Tibia/fibula AP, lateral
Ankle AP, lateral, mortise
Foot AP, lateral, medial oblique (simulated weight-bearing lateral for foot alignment abnormality)
Subtalar joint Lateral, Harris-Beath view
Calcaneus Lateral, AP craniocaudal angulated view
Toes AP, lateral, AP oblique
AXIAL SKELETON
Cervical spine AP, lateral, open mouth (odontoid); swimmer’s view for lower cervical spine, oblique or pillar views for facet joints
Thoracic spine AP, lateral; swimmer’s view for upper thoracic spine
Lumbar spine AP, lateral; oblique for pars interarticularis, flexion/extension laterals for subluxation
Sacrum 30° cephalad angulated AP, lateral
Coccyx 10° caudal angulated AP, lateral
Sacroiliac joints 30° cephalad angulated AP
Pelvis AP; Judet views and/or inlet/outlet views for pelvic ring fractures

Modified from Lee JHE: Imaging modalities. In Johnson T, Steinbach L (eds): Essentials of Musculoskeletal Imaging. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2004, p 6.

Because they have poor contrast resolution, radiographs do not reveal all aspects of arthropathy. Unlike MRI, radiography lacks the ability to show early cartilage loss and erosion, especially in the larger joints. Soft tissue pathology and muscle abnormalities cannot be assessed on radiography, as they can with MRI. Radiographs also are not as sensitive for evaluating activity of the disease. Other imaging techniques (discussed later) have these advantages and are considered complimentary to radiographs in the assessment of arthropathy.

Fluoroscopy, which employs x-ray imaging in real time, is a quick and precise method for needle placement during aspirations and injections, particularly for joints that are deep or complex and difficult to enter with the blind technique, such as the hip, shoulder, and sacroiliac joints. It can also be used to evaluate joint motion and stress. Videotaping of joint motion is useful for recording the kinematics of the joint. Because of the high dose of radiation, fluoroscopic time must be kept to a minimum. CT and ultrasonography are other imaging methods that are helpful for joint aspiration and injection (see later discussion).

Radiography transmits ionizing radiation to the patient and to medical personnel. The risk associated with this radiation, which includes carcinogenesis and genetic damage, is small but cumulative. A radiograph delivers between 0.1 to 2.0 millisieverts (mSv) to the tissue, depending on the type of tissue in the radiation path. This is less than the amount from bone scintigraphy, which tends to deliver 5 mSv, or CT, which can produce doses up to 15 mSv. The risk of cancer is estimated to be approximately 4% per Sievert by the U.S. National Academy of Sciences Committee on the Biological Effects of Ionizing Radiation. Radiation risk can be minimized with proper safety measures. The principle of the ALARA (as low reasonably achievable) dose should always be applied when using ionizing radiation. This is especially important in children and pregnant women. The number of images in one study and the frequency of follow-up studies must be prudently monitored without compromising evaluation of the joint. Appropriate collimation of the x-ray beam and reduction of fluoroscopy time should be enforced. Lead shielding of gonads and thyroid tissue is mandatory if these structures are not in the path of the body part being imaged.

Copyright © 2007 Elsevier Inc. All rights reserved. –

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