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
Synovial Fluid Analysis¶
| Non-inflammatory | Inflammatory | Septic | Hemorrhagic | |
|---|---|---|---|---|
| Appearance | Clear straw/yellow | 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), appear blue when parallel to the polarizer
- Weak birefringence significantly reduces sensitivity