Rheumatoid arthritis is an inflammatory disorder affecting multiple joints in the body. The hands and wrist, hip, knee and cervical spine are frequently involved. It is important to distinguish an inflammatory arthropathy from a degenerative process such as osteoarthritis because the clinical disease progression and, therefore, treatment are different. Imaging by conventional radiographs (X-ray), computed tomography (CT), magnetic resonance imaging (MRI), ultrasound and radionuclide bone scan, help confirm or exclude the diagnosis.
Routine X-ray Examination
Rheumatoid arthritis is a systemic condition presenting as an inflammatory arthropathy. Many joints can be affected. An inflammatory arthropathy usually presents as uniform joint space narrowing because the cartilage is rapidly destroyed, as opposed to osteoarthritis which affects localized areas of a joint more than others. Other radiographic features of rheumatoid arthritis include loss of bone mineralization (osteopenia) in the bones bordering the joints; bony erosions, and large cysts around the joint. Subluxations and joint malalignment also occur. There are basic routine X-ray views for imaging each joint: frontal view, one or two oblique views and a lateral view are standard views. At HSS, additional special views are used to increase the sensitivity of the conventional radiographic examination in detecting early changes including the Norgaard or ball catcher's view, which helps to identify subluxations and erosions.
Specialized Diagnostic Imaging Examination
Clinical signs of rheumatoid arthritis may present before they are evident on conventional (routine or special) radiographic views; MRI, CT, ultrasound and radionuclide bone scans are more sensitive for the detection of early signs of rheumatoid arthritis. MRI, using specialized surface coils, can detect early cartilage wear and both MRI and ultrasound can show inflammatory changes of the synovium and pannus formation.
Members of the Department of Radiology and Imaging at HSS are board certified radiologists with fellowship specialty training in musculoskeletal/cross sectional (CT/MR/Ultrasound) imaging. While various subspecialty physicians often perform these procedures, Radiologists are physicians specifically trained on the proper use of all forms of imaging and have specific training in the safe use of ionizing radiation (X-rays, fluoroscopy, CT) as well as MRI and safety and ultrasound optimization.
Therapeutic Intervention Performed Under Image Guidance
Anesthetic and/or steroids injected into an arthritic or painful joint or tendon sheath can help reduce the pain in rheumatoid arthritis. The advantage of having these injections performed using radiologic guidance is that one can directly visualize the needle enter the area in question thus ensuring accurate delivery of the medication. Direct visualization of the needle can be performed using fluoroscopy, CT or ultrasound guidance. A joint injection performed under fluoroscopy, which is real-time x-ray, or under CT guidance, is called an arthrogram. The radiologist injects a small amount of contrast agent into the joint to confirm accurate needle placement. With ultrasound, the radiologist directly visualizes the needle in the joint and can watch the medication enter the desired location. Additionally, the neighboring arteries, veins and nerves can be identified and thus avoided.
Rheumatoid arthritis commonly involves the hand and wrist. Some of the earliest radiographic findings include soft tissue swelling and loss of bone mineralization centered about the joints. Erosions can occur about any joint but are especially common in the metacarpophalangeal joints of the hand and well as throughout the small bones of the wrist. Later changes include deformities of the hands with subluxations of the joints and "swan-neck" and "boutonniere" deformities with flexion and hyperextension of the joints of the fingers, respectively. When obtaining standard posteroanterior radiographs of the hand, the hand is placed flat on the table; sometimes, if subluxations are present, these can reduce with this maneuver. Special views obtained at HSS include the Norgaard or ball catcher's view which allows the hands to be imaged in their normal resting state, making subluxations more visible. In addition, a small joint in the wrist called the pisiform-triquetral joint can also be seen clearly with this view.
In the knee, as in all joints affected by rheumatoid arthritis, there is uniform cartilage loss. All three joint compartments of the knee (medial, lateral & patello-femoral compartments) are uniformly affected. At Hospital for Special Surgery, we routinely obtain AP radiographs of the knee with the patient weight bearing to optimally observe early cartilage loss by identifying areas of joint narrowing. If the knee is not imaged weightbearing, the lucent joint space in the knee can appear normal, even if there is severe cartilage loss. Erosions and subchondral cysts are often seen around the knee in cases of rheumatoid arthritis. Large joint effusions, synovial thickening and inflammation and joint outpouches like a Baker's cyst are very common. These fluid corrections are easily visualized with ultrasound or MRI.
The cervical spine is commonly affected in rheumatoid arthritis. The upper cervical spine is most often involved. Ligamentous laxity and attenuation of the ligament that surrounds the first and second cervical vertebra often results in instability at this level. Because of the high incidence of subluxation in the cervical spine in patients with rheumatoid arthritis, at HSS patients with a diagnosis or suspected diagnosis of rheumatoid arthritis routinely have flexion and extension views of the cervical spine to potentially identify instability.
The lateral view of the cervical spine is obtained with the patient standing or sitting to allow for the maximum effects of gravity on the alignment of the cervical spine vertebral bodies. For the flexion view, the patient bends the neck forward as much as possible for the flexion radiograph and then tilts the neck back for the extension view. The radiologist then measures the space between the top two vertebral bodies (atlas and axis) in the cervical spine as well as alignment throughout the rest of the vertebrae to see if there is instability. Instability at the C1-2 level can result in neurological symptoms because of close proximity of the spinal cord.
Cross sectional imaging, such as CT and MR, can provide increased information about the spinal canal and the spinal cord. Early neurological changes may be evident on these imaging examinations before they are clinically apparent. The facet joints are not infrequently involved in patients with rheumatoid arthritis and erosion of the facet joints can result in instability and subluxation at other levels in the cervical spine..
Reviewed by Carolyn M. Sofka, MD.