I posted two review papers on septic arthritis on the conference page for today.
A brief summary of some historical, physical, and laboratory findings:
|Pain with motion||100%||–||–||–|
|Axial load pain||36%||–||–||–|
|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.