What are some causes of dry taps of synovial fluid?
Inability to obtain synovial fluid from a joint with an obvious effusion can be as a result of
• Synovial fluid too thick to aspirate through the lumen of a needle.
• Obstruction of the needle lumen with debris such as rice bodies (infarcted pieces of synovium in synovial fluid) or thick fibrin.
• Chronically inflamed synovium can undergo fat replacement and become markedly thickened (lipoma arborescens), so that the needle never makes it into the effusion.
• In the knee, a medial plica or medial fat pad (especially in obese patients) may block the needle. In this case, aspirate from the lateral aspect of the knee.
• Poor technique and not getting into the joint with a needle. Ultrasonography for needle placement can avoid this cause of a dry tap.