8th September 2020

A 22-year-old university student presents with a 2-week history of a swollen, painful and stiff right knee

A 22-year-old university student presents with a 2-week history of a swollen, painful and stiff right knee and right midfoot, worse in the morning. Symptoms began suddenly, with no associated trigger or trauma to the joints. He has no significant past medical history of joint problems and denies any night sweats. 6 weeks ago, he presented to his GP with dysuria and a urethral swab confirmed Chlamydia. He admits to intermittent episodes of dysuria since being treated for his STI. On examination, he is apyrexial. The knee has reduced range of motion with presence of a large effusion and is tender on palpation. Blood tests are normal except for a raised ESR. Gram staining shows no evidence of gram-negative diplococci.

For the patient above, please select the SINGLE most likely diagnosis. Select ONE option from the list above.