A 51-year-old man presented with a swollen right knee. The swelling had recurred intermittently for 10 years, staying a consistent size over the past several years. It was aspirated 3 years prior, but the swelling returned quickly. The patient had not received imaging or treatment for his knee. He experienced discomfort with kneeling, dressing, and many daily activities, but did not have knee pain. He had no injuries to the area, recent infections, or history of cancer. The patient had worked as a floor tiler for more than 20 years.

Physical examination revealed that the patient was afebrile and had a 9-cm mass below his right patella (Figure 1). The mass was compressible, fluctuant, cool, and nontender. His patella was grossly normal to palpation superior to the swelling. The skin overlying the lesion was intact, slightly violaceous, and had some desquamation. His active and passive ranges of motion were normal, and the mass did not shift position with flexion or extension of the knee.

QUESTION

Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?

• A. Gout.

• B. Osgood-Schlatter disease.

• C. Prepatellar bursitis.

• D. Septic arthritis.

• E. Superficial infrapatellar bursitis.