Septic Arthritis

I posted two review papers on septic arthritis on the conference page for today.

A brief summary of some historical, physical, and laboratory findings:

Finding Sensitivity Specificity +LR -LR
Pain with motion 100%
Effusion 92%
Fever 34-54%
Axial load pain 36%
Serum WBC 23-90 36-55 1.4-1.7 0.28-0.84
Synovial WBC > 25K 64-81 73-81 2.3-4.4 0.23-0.50
Synovial WBC > 50K 49-63 88-92 2.5-8.5 0.38-0.72
Synovial WBC > 100K 14-20 96-100 3.6-5.1 0.80-0.89
Synovial PMN > 90% 51-68 75-80 2.1-3.5 0.39-0.65
Synovial Lactate > 10 55-100 95-100 19-∞ 0-0.45

As you can see, there is no single finding which guarantees septic arthritis. Don’t rely on absence of fever to exclude a septic joint. Realize that synovial fluid findings are all over the place and are very susceptible to misinterpretation. However, if you aren’t ordering a synovial lactate it’s probably a worthwhile test to add on to everything else.

Posted in MSK