Rheumatoid arthritis, or RA as it is commonly called, is a type of inflammatory arthritis in which the body attacks itself. The immune system can no longer recognize what is self and what is invader. The area that is attacked in RA is commonly the joints of the body and more specifically the synovial tissue (the lubricating tissue in the joints). To be able to recognize this process, you will need to understand some common X-ray terminology as well as pair it together with clinical features and then discuss it with your doctor.
Terminology
Proximal--toward the beginning or nearer of the two items
Distal--the more distant item
Bilateral--pertaining to both sides
Axial--relating to or characterized by an axis
Opaque--relatively impenetrable to light
Sclerosis--A thickening or hardening of a body part
Erosions--wearing away
Ankylosis--stiffening or immobility of a joint due to fibrous or bony attachments
Bony Anatomy
Acetabulum--Socket or cup for the head of the femur
Femoral head--rounded "ball" of the femur
Femoral neck--extending off the femoral head
Clinical and Lab Features
Effects 20- to 60-year-olds with most cases first occurring in the 40- to 50-year-old range
Noticeable morning stiffness
Pain in at least one or more joints with movement
Soft tissue swelling or joint swelling in at least one or more joints
Another joint will show signs of swelling with in three months of the first one
Nodules under the skin mostly along the bony areas or thinner skin
Usually affects the hands and feet first and is symmetrical
Will usually progress toward the spine, almost always affecting the neck
Lab Findings
Elevated ESR or CRP (Both are tests to look for signs of inflammation within the body.)
Positive RA factor or RF test (The test looks for the presence of antibodies that are directed at your own tissues.)
Radiographic Findings
How advanced the RA is will will depend on the findings seen, which is why it is important to have a health professional review these findings with you along with the clinical and lab findings.
Early stages of RA will show a uniform decrease in the joint spaces (medial and axial) within the acetabulum. This finding will also be the same on the opposite hip and to the same degree. If there is swelling of the joint, the radiograph will show signs of skin lines or the movement of normal fat lines. Occasionally there will be a uniform loss of density (less opaque) in the bone, known as juxta-articular osteoporosis. This is a global decrease in the appearance of the bone. The edges of the bone may appear more opaque from the disease process, but the shaft of the bone will appear less dense.
As RA continues to progress, there will also be signs of marginal erosions or a "rat bite" appearance along the edge of the femoral head. The joint space itself will continue to decrease, and bones on either side of the joint will look more opaque and sclerotic, but only along the edges of the bone. Eventually either bony or fibrous ankylosis will set in, sometimes severe enough to fuse a joint together. In the case of the hip, what happens first is called protrusio acetabuli (where the femoral head pushes into the boney spaces of the pelvic ring).
References
- Essentials of Skeletal Radiology Volume One and Two by Terry Yochum and Lindsay Rowe 1987
- Diagrams of RA in the joint
