A 20 year old man presents with left lower back and flank pain over the last few weeks. He's also noted fever, a limp, lack of appetite, and weight loss. He has recently immigrated from sub-Saharan Africa and has not been receiving medical care. He denies alcohol, smoking, or IV drug use.
On exam, he has severe pain with extension of the hip and limited hip movement. He prefers to be in a position with hip flexion and lumbar lordosis. Laboratory studies show WBC 12,000/mL, Hgb 10 g/L, elevated ESR and CRP. A CT is shown below:
The white arrow indicates where aspiration was done. A routine gram stain and bacterial culture were sent but they are negative. Routine bacterial cultures of the blood are negative as well.
Challenge: What's the diagnosis and what is the cause?
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