Joint Effusion
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
- • Characterization of underlying arthropathy relies on disease pattern rather than single US characteristic
- • US is helpful in assessing disease activity and characterization
- • Amount and echogenicity of fluid are useful to note but lack specificity
- • If joint fluid is hyperechoic, keep joint still for several minutes
Helpful Clues for Common Diagnoses
- • Osteoarthritis
Most commonly affects knee, hip, interphalangeal, 1st carpometacarpal, triscaphe, wrist, acromioclavicular, and tarsal joints
Joint space narrowing, marginal osteophytosis, capsular swelling, synovitis, and effusion are US signs of OA
Variable increase in joint fluid
Variable degree of reactive-type inflammatory synovial proliferation
± variable periarticular inflammation
US is increasingly used to determine inflammatory component of OA and differentiate OA from crystal deposition disease or inflammatory arthropathy
Inflammatory element of OA is characterized by
Helpful Clues for Less Common Diagnoses
- • Inflammatory Arthropathy
Affects any synovial-lined joint
Ranges from single (monoarthropathy) to few (oligoarthropathy) to multiple (polyarthropathy) joint involvement
Most common finding: Pannus
Effusion may be anechoic or hyperechoic
± echogenic speckles due to precipitated fibrin or inflammatory debris
± marginal erosions
Color Doppler imaging
- – Helpful for estimating level of disease activity and distinguishing synovium from joint fluid
- – Hyperemia is more easily appreciated in smaller joints (e.g., hand, wrist, elbow) than larger joints (e.g., shoulder, hip)
- – Active pannus leads to increased color flow
- – Hyperemia is graded semiquantitatively as high, intermediate, or low/absent vascularity
- – Quantitative analysis of hyperemia is feasible, though semiquantitative analysis is adequate for clinical use
Other signs include joint space narrowing, subluxation, deformity, and ankylosis
Coexistent soft tissue features include tenosynovitis, bursitis, and entrapment neuropathy
- • Crystal Arthropathy
Always consider in any acute arthritis
Effusion can be anechoic or hyperechoic
Gout results from urate crystal deposition
- – 1st metatarsophalangeal joint is 1st affected joint in 50%; later becomes polyarticular
- – Best diagnostic clue: Identification of echogenic foci with comet-tail artifacts within and around joint
- – ± urate sand (fine punctuate echoes) or sandstorm (larger echogenic aggregates) appearance
- – ± urate deposition on articular cartilage surface as thin echogenic band (“urate icing”)
- – Soft tophi (no acoustic shadowing) → hard tophi (dense acoustic shadowing)
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