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Download the article PDF: Clinical Image Challenges November 2026
A 22-year-old male presents to urgent care complaining of a painful lump on the back of his left knee that developed roughly 3 years prior. It has gradually grown in size and discomfort since then. The lump has been growing more quickly and becoming more painful over the last month, to the point where it is difficult to play sports and exercise. Physical examination reveals normal vital signs and full range of motion and strength of the knee. A large, hard, bony, and immobile mass is visible and palpable in the popliteal fossa. It is diffusely tender to palpation. There is no erythema, induration, fluctuance, or warmth noted to the mass. There are no neurovascular deficits distal to the knee.
View the x-ray images taken and consider what your diagnosis and next steps would be. Resolution of the case is described on the following page.
