Calcium pyrophosphate crystals in synovial fluid are associated with pseudogout. Which joint is most commonly affected by pseudogout?

• A. Knee
• B. Elbow
• C. Wrist
• D. Shoulder

Answer: (A)

Calcium pyrophosphate deposition leads to pseudogout, which most often targets large weight-bearing joints, with the knee being the classic site. In older adults, an acute swollen, painful knee is a common presentation. The elbow, wrist, and shoulder can be involved but far less frequently. Synovial fluid typically shows rhomboid crystals that are weakly positively birefringent on polarized light, helping confirm the diagnosis.