Osteochondroma and Exostosis

The osteochondroma (plural osteochondromata) or exostosis (plural exostoses) or more accurately "cartilage capped exostosis" is a common developmental anomaly and represents an outgrowth from the patient's growth plate. They exist in 2 forms - a solitary form with minimal malignant potential and the familial form (multiple hereditary exostosis) which may have a risk of malignant transformation in 12 to 20% of cases. They can cause abnormalities of growth of bones if not removed at a young age. In addition they can grow into other bones and cause neighbouring bones to become deformed. These are the main reasons to have them removed even if they are well tolerated.

Figure 1. This 20 year-old male had multiple hereditary exostoses with multiple bony deformities. The lesion in his right proximal tibia continued to enlarge even in his adulthood (blue arrow). This was an indication for excision on suspicion on malignant change (sarcomatous transformation).

Figure 2. This 18 year-old female had a known lesion in the proximal tibia since she was 16(a). This was persistently painful and 3 years later had grown bigger (b). The cartilage cap was now 7 mm thick (c,d). The bone scan showed increased activity in the thickened cartilage cap (e). This very rare complication of a solitary osteochondroma occurs in less that 0.5% of such cases and the tumor should be removed on suspicion of malignant transformation.

Figure 3. This 10 year-old boy had been seen by us for an isolated osteochondroma of the right ankle (white arrows) at age 7. Although it was painful and catching in his footwear, the parents were advised not to have it removed as the adjoining growth plate could be damaged resulting in a shortened limb. At the time he had a valgus ankle (yellow arrows at left) which corrected itself 3 years later. This was apparently because the ankle talus developed a deformity to accommodate the angle (blue arrow, compared with normal ankle at inset)). As the exostosis had 'grown away' from the growth plate it was now safe to remove it without risking deformity by interrupting the growth plate.