A 22 year old man presents with pain and swelling of his right knee for 2 weeks. The pain worsens with weight bearing. There is no history of trauma. He was prescribed ciprofloxacin for an urinary tract infection around 3 weeks ago. His medical history is otherwise unremarkable. He is sexually active,
Anteroposterior, lateral and axial patellar images are obtained. These are only significant for mild soft tissue swelling and a moderate effusion.
Appearance: turbid WBC: 7,000/mm3 (< 200) PMN: 80% (< 20%) Glucose: 70 mg/dl (normal: within 10 mg/dl of serum glucose) Protein: 4 g/dl (1 - 3) Gram stain: no organisms Crystals: not seen Random plasma glucose: 80 mg/dl
Positive for Chlamydia.
The HLA-B27 assay is negative.