Septic Arthritis

Interpretation of synovial fluid:

--appearance, viscosity, cell count
--non-inflammatory synovial fluid has WBC<2,000 (and <25% pmns): nl joint or OA
--inflammatory fluid has WBC 2K-50K (and can have high pmns): ie. RA, gout, etc.
--synovial fluid WBC counts >50K, esp >100K suggest septic arthritis
--crystals in the joint fluid do not rule out an infection

--need image guidance for hip aspiration (usually done by IR or ortho)

Septic Arthritis:

• Predisposing factors include: age >80, DM, prosthetic joint, RA, recent joint surgery or intraarticular injection,  overlying skin infxn, IVDU
• Source of infection in bacterial arthritis is usually hematogenous spread (can be transient bacteremia)
• Can be the presenting sign of infective endocarditis (esp. staph, strep, enterococci)
• Septic arthritis in the hip can rarely be related to femoral venipuncture and ruptured colonic diverticulum
• Many different pathogens can cause septic arthritis (most commonly staph, strep and neisseria but gram neg infections occur in  immunosuppressed pts, gastrointestinal infxns)
• Blood cultures are positive in about 50% of cases
• Treatment involves empiric abx (vancomycin if g+ cocci, 3rd gen cephalosporin if g-, then narrow), for at least 2 weeks (if no evidence of osteomyelitis)
• Joint “washout”/drainage? No RCTs, but standard of care is joint drainage--see links below to 2 articles assessing conservative mangament (aspiration and abx) vs. open drainage (arthrotomy) for septic arthritis

(Victoria Kelly MD, 8/26/10)