How is septic arthritis diagnosed definitively? What are the temporal limitations regarding our ability to diagnose definitively? How do we get around that?
Septic arthritis is definitively diagnosed by culturing bacteria from synovial fluid. Yet diagnosis by this method is delayed due to the amount of time it takes to grow out the bacterial culture.
Waiting is bad as the damage begins once the white cells hit the joint.
While waiting for culture results, we can use a clinical decision rule to make a good guess if infection is present: COUNT THE WHITE CELLS AND ASSUME THAT A HIGH COUNT MEANS INFECTION.
(A positive gram stain may help, but it is specific, not sensitive; and even seeing “bugs” does not tell you which bug is present)
(peek into the future here