Arthrocentesis Quick Look¶

Raeann Whitney

When in doubt, tap it!¶

Send synovial fluid for Gram stain/culture and cell count
Beware: Inflammatory / crystal arthropathies can have very high leukocyte counts!
- The presence of crystals does NOT exclude septic arthritis
A fever or concern for infection in a prosthetic joint is a surgical emergency; ortho will come in the middle of the night to tap a joint
Contraindications to tap: overlying cellulitis or psoriatic plaque
- Anticoagulation / DVT ppx is OK (no need to hold)

Arthritis Type	Appearance	Total WBC	PMNs
Non-inflammatory	Straw like / yellow	\<2000	\<25%
Inflammatory / Crystalopathies	Yellow / cloudy	>2000 (often 20-50K+)	>50%
Septic	Purulent	>50,000 (often >100K)	>75%

Monosodium urate: needle-shaped, negatively birefringent
- Sensitivity is generally good (>90s%)
Calcium pyrophosphate dihydrate: rhomboid-shaped, positively birefringent (weakly)
- Weak birefringence significantly reduced sensitivity

Last update: 2022-06-27 03:29:20