Decoding the Painful Joint: Pattern, Aspirate, Plan
Joint distribution and stiffness pattern separate the arthritides at the bedside long before any laboratory result arrives. Set the three dials below and the bench names the disease and tells you which finding decided it. Then read a synovial fluid result — the test that answers the only truly urgent question — and build a treatment plan around the constraints your real patient brings with them.
1 · Which joints, and how are they arranged
2 · The stiffness
3 · The rest of the story
The aspirate answers the dangerous question firstArthrocentesis is not mainly about proving gout. It is about asking whether this is septic arthritis, which destroys cartilage within days. Set the results below.
Synovial white cell count (cells/mm3)
20012,000100,000
Differential
Polarised light microscopy
Gram stain
Serum uric acid drawn today
Who are you planning for?
What the pattern is telling you
Feature
Rheumatoid
Osteoarthritis
Gout
Pattern
Symmetric, small joints, spares the distal interphalangeal joints
Asymmetric, weight-bearing, distal interphalangeal and first carpometacarpal
Monoarticular, first metatarsophalangeal, midfoot, ankle, knee
Stiffness
Over 60 minutes, improves with use
Under 30 minutes, worsens with use
Sudden severe pain, often overnight, peaks in 12 to 24 hours
Systemic signs
Fatigue, fever, nodules, lung and eye disease
None
Occasional low-grade fever; tophi in chronic disease
Key tests
Anti-CCP, rheumatoid factor, raised ESR and CRP
Clinical; radiographic joint space narrowing and osteophytes