X-ray quiz of the day - 2

A 16-year-old girl has a painless bump behind her knee. However, she does have pain if she her leg is hit while playing soccer. On physical examination there is a firm lump behind the knee. A plain radiograph of the knee is shown.

The most likely diagnosis based on the history, physical examination and plain radiograph is:

a) High-grade intramedullary osteosarcoma
b) Parosteal osteosarcoma
c) Periosteal osteosarcoma
d) Osteochondroma
e) Periosteal chondroma

For answer, click here.