Definition
- Benign developmental aberration characterised by a cartilage capped exostosis
Aetiology
- Arises from the herniation & separation of a segment of epiphyseal growth plate cartilage through the periosteal bone cuff that normally surrounds the plate
- Can arise after radiotherapy
Epidemiology
- Usually presents in the first two decades of life, 48% in the second decade
- M>F 1.5:1
- 8% of tumours but actual incidence much higher because many are asymptomatic
Pathology
Gross Pathology
- Base of lesion has a rim of cortical bone with central cancellous bone continuous with the underlying normal shaft
- The cartilage cap varies considerably in thickness but is normally 2-3mm in thickness
- Secondary chondrosarcomas are usually at least 2cm in thickness
- A cartilage cap in excess of one cm thickness or 5cm diameter is suggestive of malignancy
- Cystic change within the cartilage cap is cause for concern
- The cartilage cap thins as the patient ages
Histology
- Towards the base of the lesion the chondrocytes line up in columns simulating the appearance of the epiphyseal plate, & there is maturation into trabecular appearing bone
- Spindle cell differentiation should suggest the diagnosis of parosteal osteosarcoma
Clinical
- Presents as pain or a mass
- There can be a clicking or inflammation of tendons running over the mass
- May be an overlying bursa, which can be confused with a secondary chondrosarcoma
- Usually occurs in long bones, particularly around the knee (distal femur, proximal tibia & the proximal humerus). Can occur in any bone that undergoes enchondral ossification
- Uncommon in the bones of the hand
- Usually occurs in the metaphysis
- After adolescence & closure of the growth plate there is usually no further growth
- Further growth at this stage could herald malignant change & the lesion should be excised
- Malignant change probably occurs in 1%
Investigations
X-rays
- Flattened (sessile) or stalk like (exostosis) protuberance in a juxta-epiphyseal location (i.e. in the metaphysis)
- The protuberance normally points away from the joint
- The cortex of the osteochondroma is contiguous with the normal cortex, & the medulla is contiguous with the medulla of the host bone
- Extensive calcification with radiolucent irregularities of the cap implies possibly malignant change.
Treatment
- Surgical excision flush with the host bone is indicated if the lesion is painful, unsightly, producing disability or may be undergoing malignant change.
- Recurrence occurs in only around 2% & suggests that the original tumour was a chondroma
See Also
- Multiple osteochondromas (hereditary multiple osteocartilaginous exostoses, diaphyseal aclasis)
- Epiphyseal osteochondroma – dysplasia epiphysealis hemimelica – Trevor’s disease
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.