The specimen is the upper end of the fibula showing a fusiform swelling some 7 cm in length. The
cut surface shows a multilocular cyst containing blood.
This boy presented at the age of 14 with a week's history of swelling on the outer side of
the leg just below the knee. Some months before he had twisted his leg with an external rotation
force during a soccer game. On examination a hard mass was found in the upper fibula which was
slightly tender and was warmer than the surroundings. An X-ray showed an aneurysmal bone cyst.