This 27-year-old male presents with pain and swelling in the anterior left knee. The symptoms began eight months prior. There was no known injury or previous surgery.
Have a look at images 1 through 3, and see if anything stands out. Do not be distracted by the obvious finding.
The images show normal menisci, ligaments, and tendons. There is a large joint effusion. A normal plica is visible, which is not thickened.
If you look closely in the posterior aspect of the suprapatellar joint capsule, there is frond-like synovitis or pannus (images 4 through 6, green arrows). Therefore, the most likely diagnosis is rheumatoid arthritis or seronegative arthropathy. In certain continents, Lyme disease would be a differential. Gout is more common in older patients.
It is important to correlate the findings, and not be distracted by prominent plica, which would not cause the degree of joint effusion.
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