Evaluation of any articular disorder involves imaging the affected joints with the most appropriate modality. Imaging documents not only the extent and severity of joint involvement but also the progression or regression of disease. More importantly, in the patient who presents with vague, complex, or confusing clinical symptoms, imaging often allows a specific diagnosis to be made. The modalities available for imaging are radiography, magnetic resonance imaging, ultrasonography, computed tomography, and bone scintigraphy. The role that each of these modalities may play in the evaluation of the patient with articular disease is discussed.
Radiography
Evaluation of articular disease should begin with the radiograph, which is the best modality to evaluate accurately any subtle change occurring in the bone. If high quality radiographs are obtained in properly positioned patients, accurate evaluation can often be made without further studies. The vast majority of modern radiology departments use computed radiography (CR) or digital radiography (DR) imaging equipment rather than film screen systems. Digital images from either of these modalities have lower spatial resolution than film screen systems but have comparable sensitivity to film for the detection of erosions and offer superior evaluation of the soft tissues. Tight collimation and proper exposure are critical for the optimization of a digital radiograph, and the imaging of both hands simultaneously on a large cassette or detector should be avoided with these systems. Digital radiography should be optimized with vendor-specific reconstruction algorithms and exposure factors. Optimum digital image quality can be dependent on the picture archival and communication system (PACS system) accepting vendor-specific correction factors, so the compatibility of imaging equipment and the PACS system should be verified at the time of equipment purchase and after any equipment software upgrade.
Evaluation of a digital image at a workstation is optimized by using high quality, high resolution, lumens balanced monitors that are calibrated frequently. Digital images, particularly of the hands and feet, should be magnified, panned, windowed, and leveled to be completely assessed.
For those departments still using film, the high quality study demands that high resolution, fine detail imaging system be used, especially in the extremities, to detect subtle disease. There are numerous film–screen combinations available, and the system used depends upon the individual radiography department. Generally, the lower the system speed, the higher the resolution. Most departments employ a single screen–film combination with system speeds of 80 to 100 for this necessary resolution.
The symptomatic joint should be imaged in appropriate positions. It should be radiographed in at least two different projections. Although one view may appear entirely normal, a second view taken at 90-degree angle to the first view may show significant abnormality ( Fig. 1-1 ). Special views are available and should be used when imaging specific joint articular diseases. The important positions for several of the joints commonly imaged are discussed hereafter.
Hand and Wrist
The posterior (PA) and Nørgaard views of the hands and wrists provide the most information if only two views are to be obtained. The PA view gives information on mineralization and soft tissue changes. The Nørgaard view is used to demonstrate early erosive disease. The Nørgaard view is an anterior-posterior oblique view, or the oblique view opposite that which is routinely obtained. It has been described as the “You’re in good hands with Allstate” or “ball-catcher’s” view. It profiles the radial aspect of the base of the proximal phalanges in the hand and the triquetrum and pisiform bones in the wrist ( Fig. 1-2 ). The earliest erosive changes of any inflammatory arthropathy begin in these areas. Erosive changes occur between the triquetrum and pisiform before they occur around the ulnar styloid process ( Fig. 1-3 ). The Nørgaard view will also reveal the reducible subluxations of inflammatory arthropathies and systemic lupus erythematosus, as the fingers are not rigidly positioned by the technician in this view ( Fig. 1-4 ).
Foot
The anteroposterior (AP), oblique, and lateral views of the foot are usually obtained. One must be sure to obtain a high quality radiograph of the calcaneus in the lateral view. Observation of the attachments of the plantar aponeurosis and Achilles tendon is important in many of the arthropathies ( Fig. 1-5 ).
Shoulder
Anteroposterior views of the shoulder should be obtained in true external and internal rotation. Erosive changes can usually be identified in at least one of these views. External rotation is best for demonstrating the presence of osteophytes. Internal rotation demonstrates the traumatic lesion of the Hill-Sachs defect. Location of tendon calcification can be determined by observing change in the position of the calcification between the internal and external rotation. The straight AP view does not image the true glenohumeral joint. In order for this joint to be imaged accurately, the patient should be placed in a 40-degree posterior oblique position ( Fig. 1-6 ).
Knee
The AP radiograph of the knee should be obtained in the standing position. This allows for accurate evaluation of loss of cartilage. If the patient is not standing, then the medial and lateral compartments may appear perfectly normal ( Fig. 1-7 ). In the standing position there may be asymmetry between the medial and lateral compartments, but unless the joint space measures less than 3 mm, cartilage loss is not the cause. The discrepancy between the compartments may be secondary to ligamentous instability. The standing AP view demonstrates displacement of the tibia on the femur and any pathologic degree of varus or valgus angulation. The knee should also be radiographed in a nonstanding lateral flexed position. This allows evaluation of the patellofemoral joint space as well as identification of an abnormal position of the patella. If the knee is flexed 45 degrees or more, then medial and lateral compartment narrowing can also be observed. On the lateral view, the medial plateau is the white line that curves downward; the lateral plateau is a white line that goes straight across or curves upward ( Fig. 1-8 ).
Hip
The hip is usually radiographed in the AP and frog leg positions. In the AP view the hip is internally rotated to image the femoral neck to its fullest advantage. In the frog leg lateral view the hip is abducted. In this view, the anterior and posterior portions of the femoral head are imaged. This view is most important in evaluating underlying osteonecrosis. Although the entire head may appear to be involved on an AP view, the frog leg lateral view may demonstrate the abnormality to be limited to either the anterior or posterior section of the head. It is also the frog leg lateral view that demonstrates a subchondral lucency of osteonecrosis. In many patients, a vacuum phenomenon in the joint will be produced in the frog leg lateral view, helping to exclude the presence of synovial fluid. The vacuum phenomenon may also help in the evaluation of the cartilage present ( Fig. 1-9 ).
Sacroiliac Joints
The modified Ferguson view is the only view necessary to evaluate the sacroiliac joints ( Fig. 1-10 ). The patient is placed in a supine position and when possible, the knees and hips are flexed. The x-ray tube is centered on L5 to S1 and then angled 25 to 30 degrees toward the head. If it is angled too steep, the pubic symphysis will overlie the sacroiliac joints and obscure them, preventing accurate evaluation. The modified Ferguson view brings into profile the anterior/inferiormost aspect of the sacroiliac joints. It is this part of the joint that is most frequently affected in any disorder of the sacroiliac joints. Ninety percent of the time this view provides the clinician with an image that can be accurately evaluated. Computed tomography and magnetic resonance imaging (MRI) may also be used if the pelvic soft tissues cause a problem in the plain film radiograph.
Cervical Spine
The lateral flexed view of the cervical spine is the single most important radiograph in the evaluation of cervical spine disease. Flexion opens the apophyseal joints and allows accurate observation of erosive disease. It demonstrates significant subluxation of one vertebral body on another. It also demonstrates abnormal laxity of the transverse ligament, which holds the odontoid adjacent to the atlas ( Fig. 1-11 ). This finding is common in all inflammatory arthropathies but especially in rheumatoid arthritis.
Diagnostic Radiographic Survey
The distribution of the joint involvement is key to the diagnosis of the specific arthropathy. Therefore, it is also necessary to obtain radiographs of more than just the symptomatic joint. Simple radiographic surveys can be performed, tailored to the working clinical diagnosis. For example, if ankylosing spondylitis is the working diagnosis, then the survey should be tailored to the axial system; if rheumatoid arthritis is the working diagnosis, then the survey should be tailored to the appendicular system. For the patient with vague articular complaints that fit no specific pattern, the following “poor man’s” survey would be appropriate:
- 1.
Posteroanterior and Nørgaard views of both hands to include both wrists
- 2.
Anteroposterior standing view of both knees
- 3.
Anteroposterior view of the pelvis
- 4.
Lateral flexed view of the cervical spine
This survey will provide sufficient diagnostic information while exposing the patient to a relatively low dose of radiation at a reasonable cost.
Magnetic resonance imaging
Magnetic resonance (MR) imaging has made a major impact on the detection and evaluation of joint-based disease and is the most important imaging technique after radiography. This modality offers accurate, noninvasive assessment of pathology affecting joints, bone marrow, soft tissues, and the spine. It offers many advantages when compared to plain radiographs, including superior evaluation of soft tissues, marrow, and cartilage; lack of ionizing radiation; multiplanar evaluation of joints too difficult to image by plain radiography (e.g., temporomandibular joints and spine); and, if a contrast agent is necessary, an alternative agent (gadolinium) for individuals sensitive to iodine. The clinical and research use of MR imaging in the evaluation of arthropathies has expanded rapidly in an effort to exploit these advantages.
However, the advantages of MR imaging of the joint must be balanced against the cost of the examination, the length of the examination, and the discomfort for the patient. The use of MR in the evaluation of arthropathies can be separated into two categories: (1) assessment of complications of arthropathies, and (2) verification of an arthropathy and assessment of response to treatment. The use of MR in the primary evaluation of synovitis, detection of early erosions, and status of the articular surface is much more common now than it was 10 years ago. The problem with MR from a diagnostic perspective is that the examination is sensitive but not necessarily specific for the diagnosis of arthropathies. MR images should always be correlated with available radiographs whenever possible.
The inherent contrast resolution of MR offers the opportunity to evaluate the synovium, bone marrow, cartilage, soft tissues (ligaments, tendons, and muscle), and spine.
MR: Synovium
MR imaging can demonstrate disease of synovial-lined structures including synovitis, tenosyn-ovitis, synovial cyst, and bursitis. The majority of these findings have been most extensively studied in rheumatoid arthritis but can be seen in any of the inflammatory arthropathies, infection, and even osteoarthritis. The MR demonstration of synovitis may be very important to the rheumatologist, if the physical examination is equivocal in establishing the diagnosis of an inflammatory arthritis or determining the effect of a particular treatment regimen on the synovium. Some investigators say that they can differentiate synovium from effusion on noncontrast spin echo images. Normal synovium is usually imperceptible on MR. Hypertrophied synovium may demonstrate intermediate signal on T1-weighted images relative to the low signal of joint effusion and show intermediate signal on T2-weighted images compared to the relatively high signal effusion ( Fig. 1-12 ).
However, frequently synovitis cannot be differentiated from effusion without the use of intravenous gadolinium. Active synovitis enhances with the administration of gadolinium ( Fig. 1-13 ), but the affected joint must be imaged immediately, as gadolinium will diffuse into the joint if imaging is delayed. This rapid diffusion of gadolinium precludes postcontrast imaging of joints outside the initial field of view.
Nonspecific synovitis is usually intermediate in signal on T1- and T2-weighted images. When the synovium is low in signal on T2-weighted images, the differential diagnosis becomes limited to the following: pigmented villonodular synovitis (PVNS), calcified synovial chondromatosis, hemophilia, amyloidosis, and chronic rheumatoid arthritis. The typical MR appearance of PVNS is foci of intermediate to low signal within the synovium, secondary to hemosiderin deposition, on T1- and T2-weighted images ( Fig. 1-14 ). The diagnosis of synovial chondromatosis is suggested by the MR appearance of noncalcified loose bodies demonstrating intermediate signal on T1-weighted images and high signal on T2-weighted images ( Fig. 1-15 ).
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