A 44-year-old male presents to the emergency room with an acutely swollen right knee

A 44-year-old male presents to the emergency room with an acutely swollen right knee. He has been in good health, and he has no chronic health conditions and no history of trauma. 

The most important evaluation should be:
A. MRI of the knee
B. Erythrocyte sedimentation rate
C. Diagnostic arthrocentesis of the knee
D. Complete blood count
E. Rheumatoid factor

Answer: C. Diagnostic arthrocentesis of the knee

Discussion: Although all of these tests might ultimately be useful, the most immediate concern is to rule out an infection, which could cause permanent disability, even mortality. Arthrocentesis is critical for almost every patient with monoarticular joint disease

The patient in the above question has appropriate laboratory evaluations drawn. In the meantime, the decision is made to perform an arthrocentesis. 

Which of the following is a true statement concerning this examination?
A. A synovial fluid WBC count of less than 2,000 cells/mm3 suggests an inflammatory process.
B. The presence of needle-shaped crystals is a normal finding.
C. The presence of crystals excludes the possibility of an infection.
D. Cloudy synovial fluid would be consistent with an inflammatory process.
E. The finding of fat droplets is to be expected.

Answer : D. Cloudy synovial fluid would be consistent with an inflammatory process.

Discussion: Synovial fluid analysis is an important diagnostic procedure in the patient with monoarticular arthritis. Normal synovial fluid should be clear, whereas cloudy fluid suggests an inflammatory arthritis. The presence of needle-shaped crystals suggests monosodium urate crystals. The presence of crystals does not exclude the possibility of infection. Fat droplets suggest a fracture.