1. INTRODUCTION
Osteochondromas (OC) are benign tumors that account for 20-50% of
benign and 10% of all bone tumors. The incidence rate of OC in males is
twice that of females and its peak is usually in the second decade of
life (1). These lesions are inherited in an autosomal dominant manner
and cause the formation of isolated lesions or multiple exostoses during
the development of bones in the process of enchondral ossification in
the long bones (2). Also, OC is associated with the mutation of some
tumor suppressor genes, including EXT1 or EXT2 genes. OC have a
periosteal origin and are formed in the active parts of bones, including
the metaphysis of long bones and the cartilage at their ends. Studies
show that OC can be caused after surgery/radiation-induced injury and
hematopoietic stem cell transplantation (3).
Osteocartilaginous exostosis is mainly detected in childhood and in the
form of palpable masses, with chronic pain and sometimes with edema (4).
The presence of misplaced bone masses in the joint capsule and sometimes
with cartilaginous coating in radiographic images is one of its common
manifestations. The most common joints involved in OC are the hip and
knee joints. Patellar OC is rare and mostly affects the patellar bursa.
Moraes et al. (2014) reported a patellar OC measuring 8 × 6 × 3 cm
anterior to the patella in a 60-year-old man who was painless and
without limitation of flexion-extension in the knee joint (5). In the
present case, rare retro-patellar OC was observed in the area of the
patellar ligament.