Imaging Techniques and Modalities

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 ).