Is there a pattern approach to interpreting a plain radiograph for arthritis?
In assessing a skeletal radiograph, a pattern approach using the mnemonic ABCDES can be very helpful.
A —Alignment: Rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) are characterized by deformities, such as ulnar deviation at metacarpophalangeal (MCP) joints.
—Ankylosis: Seronegative spondyloarthropathies frequently cause ankylosis. Prior surgery or infection is an additional cause.
B —Bone mineralization: Periarticular osteopenia is typical of RA or infection and is rare in crystalline arthropathy, seronegative spondyloarthropathies, and degenerative joint disease (DJD) (osteoarthritis [OA]).
—Bone formation: Reactive bone formation (periostitis) is the hallmark of seronegative spondyloarthropathies. Osteophytosis is seen in DJD and calcium pyrophosphate deposition disease (CPPD) and can be present in any end-stage arthritis.
C —Calcifications: Soft tissue calcific densities may be seen in gouty tophi, SLE, or scleroderma. Cartilage calcification is typical of CPPD.
—Cartilage space: Symmetric and uniform cartilage loss results in radiographic joint space narrowing that is typical of inflammatory disease. Focal or nonuniform joint space loss in the area of maximal stress in weight-bearing joints is the hallmark of OA.
D —Distribution of joints: A symmetric distribution of affected joints suggests an inflammatory arthropathy such as RA, whereas OA commonly results in asymmetric joint involvement. Also, target sites of involvement may facilitate differentiation of arthritides (e.g., distal interphalangeal joint involvement [DIPs] is common in OA and psoriatic arthritis).
—Deformities: Swan neck or boutonniere deformities of the hands are typical of RA.
E —Erosions: In addition to their presence or absence, the character of erosions may be diagnostic, such as overhanging edges and sclerotic margins in gout. Marginal erosions are more suggestive of an inflammatory arthropathy such as RA.
S —Soft tissue and nails: Look for distribution of soft tissue swelling, nail hypertrophy in psoriasis, and sclerodactyly in scleroderma.
—Speed of development of changes: Septic arthritis will rapidly destroy the affected joint.
Pearl: When obtaining radiographs on patients with arthritis, always order weight-bearing radiographs to evaluate joint space narrowing in lower extremity joints (hip, knee, ankles).