An osteochondroma or exostosis is a bony projection of the surface of a bone capped by cartilage.
It is the second most common benign primary bone tumour after non-ossifying fibromata.
This condition affects males and females equally in their first decade, and usually found in the lower femur, upper tibia and upper humerus i.e. the metaphysis of long bone.
The condition can be single or multiple, the later is associated with a 20% rate of malignancy, compared to less than 1% in the presence of a solitary tumour.