Chapter 219

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).

###### Figure 219-1.

A: Solitary osteochondroma involving the distal left femur. B: Clinical photograph in the operating room showing the resected specimen.

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 studies undertaken.

### Treatment

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 ...

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