Question
A 10 year old boy has several bony lumps around his knees. His father had similar lumps removed.
- What is the diagnosis and its genetics?
- What deformities are associated?
- What are the indications for surgery and the warning signs of malignancy?
Answer
Diagnosis
- Hereditary multiple exostoses (multiple osteochondromas)
- Autosomal dominant mutation of EXT1 or EXT2
- EXT1 mutations cause more severe disease
- Lesions are sessile or pedunculated and point away from the joint
Deformities
- Short stature
- Forearm deformity with ulnar shortening, radial bowing and radial head dislocation
- Genu valgum and ankle valgus
- Limb length discrepancy
Surgery
- Pain, nerve or vessel compression and tendon irritation
- Deformity correction with guided growth, ulnar lengthening or osteotomy
- Excision after skeletal maturity lowers recurrence
Malignancy
- Secondary chondrosarcoma is more frequent than with a solitary osteochondroma
- Warning signs are growth after skeletal maturity and new pain
- Cartilage cap over 2 cm on MRI in an adult
Related pages
Author Contributions
Orthofracs team
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.