Patients are typically asymptomatic, and osteochondroma is often discovered incidentally. However, if patients experience pain, it is likely due to mechanical effect on nearby structures. Less commonly, pain is due to pathologic fracture of the stalk.
Osteochondromas may cause paresthesia or muscle weakness due to compression of the nearby nerves such as the common peroneal, sciatic, or radial nerve. The nearby vasculature may also be compressed by an osteochondroma and result in pseudoaneurysm, acute ischemia, phlebitis, and claudication. Pseudoaneurysm may be seen with posterior osteochondromas about the knee as flexion repeatedly traumatizes the popliteal artery. Since the lesion projects off the surface of the bone, patients may complain of cosmetic abnormalities.
The risk of malignant transformation of a solitary osteochondroma into chondrosarcoma is less than 1% and may be correlated with a cartilage cap thicker than 2 cm in adults and 3 cm in children. It is typical and acceptable to notice growth of an osteochondroma that coincides with childhood growth. After closure of the growth plate, increased pain and growth of osteochondroma should raise suspicion for malignancy.
Prevalence: Osteochondroma is a cartilage tumor that presents within the first 4 decades of life. It is the most common benign bone tumor and accounts for 30% of benign bone tumors.
Causes / typical injury mechanism: One theory is that solitary osteochondroma formation is secondary to growth plate injury during childhood.
Pathophysiology: The pathophysiology of osteochondroma involves disruption of endochondral ossification. This is typically sporadic but may be due to radiation or a fracture of the growth plate. The epiphyseal cartilage is displaced to the subperiosteal region, where it grows with its characteristic cartilage cap. This mass stops growing and the cap ossifies once the patient reaches skeletal maturity. The cartilage cap may resorb, leaving a sharp, bony spike in its place that may aggravate nearby structures.
Variants: In 85% of cases, osteochondroma presents as a solitary lesion that is nonhereditary, but there are other variants of osteochondroma:
- Multiple hereditary exostosis (MHE)
- Multiple osteochondromas (disease severity varies)
- Occurs at a younger age, with male predominance
- Rare autosomal dominant inheritance of 1 in 50 000
- Associated with exostosin (EXT1 and EXT2) genes that affect the prehypertrophic chondrocytes of the physis
- More likely to have disease involving the axial skeleton
- May result in decreased range of motion, limb length discrepancy, and limb deformity
- Risk of malignant transformation to chondrosarcoma is between 1% and 10%. There is no correlation between malignant transformation and EXT mutation, gender, severity of disease, or number of lesions.
- Dysplasia epiphysealis hemimelica (Trevor disease)
- Rare variant located at the epiphysis
- Male predominance
- Commonly located at the knee and ankle, although most patients have involvement of multiple bones, typically asymmetrically
- Sequela involves early degenerative joint disease if not treated