Imaging of benign complications of exostoses of the shoulder, pelvic girdles and appendicular skeleton

Exostoses are the most common benign bone tumors, accounting for 10 to 15% of all bone tumors. They develop at the bone surface by enchondral ossification and stop growing when skeletal maturity has been reached. At first, exostoses are covered by a smooth cartilage cap that progressively ossifies with skeleton maturity. Then they may regress, partly or even completely. Osteochondromas may be solitary or multiple, with the latter associated with hereditary multiple exostoses (HME). Exostoses develop during childhood and become symptomatic during the third decade of life in the case of solitary exostoses, or earlier, in case of HME. They stop growing after puberty, when the epiphyseal plates close. Most exostoses remain asymptomatic. Local complications, usually benign, may occur, such as fractures or mechanical impingements upon nearby structures. In rare cases, sarcomatous degeneration occurs. Most of these complications have been described in case reports. This article describes the imaging features of benign complications of exostoses of the shoulder, pelvic girdles and appendicular.