This image is a synovial fluid smear from a patient on chemotherapy who developed septic arthritis due to Haemophilus influenza infection. Notice the extracellular rods and the very rare intracellular rods present in this smear (see arrows). The difficulty in observing these organisms shows the importance of having a well-distributed cytospin and a good stain.
Joint fluids are more viscous than other fluids; making a good smear can be difficult. Sometimes making the smear from a saline dilution of the fluid works better.