Imaging for Rheumatoid Arthritis: An Overview

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, especially x-ray (conventional radiograph), CT, MR, Ultrasound and Radionuclide Bone Scan, can each help confirm or exclude the diagnosis.

Conventional Radiographs

Routine X-ray Examination

Rheumatoid arthritis is a systemic condition presenting as an inflammatory arthropathy. Many joints can be affected. An inflammatory arthropathy presents as uniform joint space narrowing, 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 (osteoporosis) 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: an AP (anterior posterior or frontal view), one or two oblique views and a lateral view are standard views. At Hospital for Special Surgery, special x-ray views designed to increase the sensitivity of the conventional radiographic study in detecting early changes are typically used in place of or in addition to the standard views. These findings can occur in any joint, but most often occur in the hand.

Specialized Diagnostic Imaging Examination

Clinical signs of rheumatoid arthritis may be evident before it is evident on conventional (routine or special) radiographic views. At Hospital for Special Surgery, MRI, CT, Ultrasound and Radionuclide Bone Scans are used in certain instances because they are more sensitive for the detection of early rheumatoid arthritis. MRI can detect early cartilage wear earlier than radiographs. Also, MRI and ultrasound can show inflammatory changes of the synovium and pannus formation.

• MRI is very sensitive to bony and soft tissue changes. MRI can also demonstrate reactive bone edema or soft tissue swelling as well as small cartilage or bone fragments in the joint. MRI performed with appropriate dedicated protocols for the musculoskeletal system is very sensitive. At HSS, specific cartilage pulse sequences are used to identify early evidence of cartilage degeneration. When there is objective evidence of cartilage wear, appropriate treatment can be initiated to prevent or delay progression.
  
• CT is excellent for demonstrating the degree of osteophyte (bone spur) formation and their relationship to the adjacent soft tissues. CT is also useful to provide guidance for therapeutic and diagnostic procedures.
  
• Ultrasound is extremely sensitive for identifying synovial cysts and outpouches that can form in association with osteoarthritis. Ultrasound can also be used to image articular cartilage in patients who cannot tolerate an MRI examination and can also be used to guide for diagnostic and therapeutic procedures.
  
• Radionuclide Bone Scans are very sensitive in detecting reactive bone edema association with osteoarthritis. Bone scans can also image the entire skeleton in one examination and thus can provide the clinician with helpful information in patients who there are multiple sites of arthritic involvement.

Members of the Department of Radiology & Imaging at HSS are Board certified Radiologists with Fellowship specialty training in musculoskeletal imaging/cross section (CT/MR) imaging. While various subspecialty physicians perform these procedures, Radiologists are physicians trained to use all forms of imaging and have specific training in the safe use of ionizing radiation (fluoroscopy, CT) as well as MR safety and MR and ultrasound physics.

Therapeutic Intervention Performed under Image Guidance

Anesthetic and/or steroids injected into an arthritic or painful joint can help reduce the pain. The advantage of having these injections performed using radiologic guidance is that one can directly visualize the needle tip in the joint space.  Direct visualization 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 will inject 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 as well as neighboring muscles, arteries and veins.

Specific Joints

Hand

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 carpal bones of the wrist. Later changes include deformity 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 Hospital for Special Surgery include a Norgaard or ball catcher's view. The Norgaard or ballcatcher's view allows the hands to be imaged in their normal resting state, making subluxations more visible. In addition, a small bone in the wrist called the pisiform can also be seen clearly with this view.

Knee

As in all joints affected by rheumatoid arthritis, in the knee, 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 or laxity. If the knee is imaged not weightbearing, the lucent joint space in the knee can appear normal, even if there is severe cartilage loss. Osteophytes (or bone spurs) are not typical in rheumatoid arthritis, as opposed to osteoarthritis. Erosions and subchondral cysts, however, 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.

Cervical Spine

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, at Hospital for Special Surgery patients with a diagnosis or suspected diagnosis of rheumatoid arthritis routinely have flexion and extension views of the cervical spine. 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.

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posted 11/6/2008