Osteochondroma, a cartilage-capped bony projection protruding
from the surface of a bone, is the most common benign bone tumor.
It reportedly accounts for 36% to 41% of all bone
tumors.1 More than 50% of solitary osteochondromas
occur in the metaphyseal area of the knee (distal femur and proximal
tibia) and shoulder (proximal humerus) (Fig. 219-1).
Its cause is related to a localized herniation of a portion of
the growth plate which results in the formation of a cartilage-capped
eccentric small bone. Unlike the more extensive hereditary (autosomal
dominant) multiple exostoses, solitary osteochondromas do not appear
to be genetically transmitted.
The tumor often resembles a cauliflower. The surface usually
is lobular, with multiple bluish-gray cartilaginous caps covering
the irregular bony mass. The cartilaginous cap is usually 1 to 3
mm thick, but in the younger patient it may be noticeably thicker. The
thickness of the cartilaginous cap may be much greater if the tumor
has undergone sarcomatous change.
In the majority of patients, the osteochondroma becomes evident
between the ages of 10 and 20 years, with a slight male preponderance.
An osteochondroma may be discovered as an incidental radiographic
finding, or it may be detected by the patient who feels a protruding
bump. Other factors that often draw attention to the osteochondroma
include localized pain, growth disturbance, limited joint motion, or
abnormal cosmetic appearance.
On the radiograph, the cortex and cancellous bone of the osteochondroma
blend with the cortex and cancellous bone of the normal bone. This
is the main radiographic finding, and any deviation from this feature
should raise suspicion of a more serious lesion. Steady growth of
the cartilaginous cap is acceptable during childhood and early adolescence,
but growth should cease when skeletal maturity is reached. If the
cartilaginous cap continues to grow after skeletal maturity, malignant
transformation should be considered and the appropriate follow-up
Because a solitary osteochondroma is a benign tumor, it does
not need to be surgically excised if it is asymptomatic. Excision
usually is reserved for those lesions that cause pain or symptomatic impingement
on neurovascular structures or that interfere with joint function.
Pain usually becomes an issue when an osteochondroma is repeatedly
bumped on its prominence. Sometimes the osteochondroma is considered
cosmetically unacceptable and the adolescent will ask to have it
removed, preferring a scar to a bump. Malignant degeneration of
a peripheral solitary osteochondroma can lead to chondrosarcoma
in adulthood. However, malignant degeneration of solitary osteochondromas
is rare, probably happening in less than 0.25% of lesions. The prognosis
following excision of a chondrosarcoma is excellent.