Arthrocentesis Quick Look
Tina Arkee
Indications for arthrocentesis
- Monoarthritis (acute or chronic)
- Suspicion for infection, crystal arthropathy, or hemarthrosis
- Trauma with joint effusion
- When diagnosis is unclear despite history and other workup
Relative Contraindications to arthrocentesis
- Extensive cellulitis or psoriatic plaque around the site of interest (risk of introducing bacteria into a sterile space)
- Coagulopathy
- Bacteremia
- Concern for infection of a prosthetic joint – these should only be tapped by Ortho!
What to order
- Synovial fluid exam (includes cell count and crystal exam). *Note: may see similar cell counts in gout and septic arthritis. The presence of crystals does not necessarily rule out septic arthritis.
- Body fluid gram stain and culture
Who should tap? Typically, start by consulting the service appropriate for the clinical entity highest on your differential (i.e. orthopedics if concern for septic arthritis; rheumatology if concern for gout)
Synovial fluid analysis
Non-inflammatory |
Inflammatory |
Septic |
Hemorrhagic |
|
|---|---|---|---|---|
| Appearance |
Clear |
Clear to cloudy yellow |
Opaque/turbid yellow green |
Reddish brown |
| Cell count | <2000 | >2000–50,000 | >50,000 | <2000 |
| % of PMNs | <25% | >50% | >75% | <50% |
| Culture | Negative | Negative | Positive | Negative |
| Crystals | No | Yes Gout: needle shaped, negatively birefringent Pseudogout: rhomboid shaped, positively birefringent |
No | No |
| DDx | Osteoarthritis, trauma, osteonecrosis | Inflammatory arthritis, crystal arthritis, sarcoidosis, indolent infections | Septic arthritis | Trauma, coagulopathy |
Crystals
- Monosodium urate: needle-shaped, negatively birefringent
- Sensitivity is generally good (>90s%)
- Calcium pyrophosphate dihydrate: rhomboid-shaped, positively birefringent (weakly), ane appear blue when parallel to the polarizer
- Weak birefringence significantly reduces sensitivity