Subungual exostosis (osteochondroma) of the toes

What is subungual exostosis?

Subungual exostosis is a type of osteochondroma. Osteochondromas are growths made up of bone and cartilage from the growth plate. They typically develop in children between 10 and 15 years of age, but can occur in younger children. Osteochondromas form near or on the surface of a bone, usually near the end that is growing (at the growth plate) and where the tendon inserts into the bone. These growths can be found on the arms, legs, knees and at the ends of the toes or fingers under the nail (subungual exostosis).

Subungual exostosis is commonly found on the toes and most frequently on the end of the big toe. The lesions get larger throughout childhood but typically do not change in size after the child has finished growing.

What are the signs and symptoms of subungual exostosis?

Children typically present with a painless mass but as the lesion grows symptoms can develop that include:

• pain
• nail deformity
• changes to the nail bed
• a hard bump near a joint or under a toenail
• a growing lesion that stops growing when the child's growth stops

How is subungual exostosis diagnosed?

Children typically present with a painless mass that feels like a hard bump near a joint or under a toenail. A health-care provider will perform a physical exam of the affected foot and toes to check the bump, the range of motion of nearby joints and to assess the nailbeds. If a subungual exostosis is suspected, then an X-ray can be done to confirm the diagnosis.

The primary care provider might repeat X-rays as your child grows to check that the subungual exostosis is not growing too quickly. They may also order other tests after their assessment including:

• CT scan
• MRI

How is subungual exostosis treated?

At initial diagnosis, if there are minimal or no symptoms, then the treatment is observation.

Surgery may be considered if there are persistent symptoms of pain and deformity of the nail, bleeding, infection and footwear concerns. In most children, it is best to wait until they have finished growing before doing surgery to remove the subungual exostosis. This will help to minimize the chance of it recurring.

During surgery the nail is carefully elevated to allow for the removal of the entire lesion. The nail bed is then closed with stitches, taking care to make sure there is minimal disruption to the nail bed to help prevent complications.

Removal of a subungual exostosis in a growing child is only recommended when the lesion causes pain, deformity, infection or bleeding and is not based on the size of growth.

At SickKids

If symptoms of pain and deformity of subungual exostosis are persistent then a referral to SickKids is reasonable.

All referrals require photos of the feet. For subungual exostosis, please include a directed photo of the affected toe.

Resources

If you are concerned about exostoses in other areas of the body, please click this link: (MHE) Hereditary Multiple Osteochondromas. Please note, patients with MHE do not get subungual exostosis.

References

Mosca, V. (2014). Principles and Management of Pediatric Foot and Ankle Deformities and Malformations (1st ed.). Wolters Kluwer Health

Bouchard, M., Bartlett, M., & Donnan, L. (2017). Assessment of the Pediatric Foot Mass. Journal of the American Academy of Orthopaedic Surgeons. 25(1), 32-41. https://doi.org/10.5435/JAAOS-D-15-00397

OrthoKids – Pediatric Orthopaedic Society of North America. (n.d.). Osteochondroma. https://orthokids.org/conditions/osteochondroma/

Paras, T. (2024, October 10). Osteochondroma & Multiple Hereditary Exostosis. Orthobullets. https://www.orthobullets.com/pathology/8020/osteochondroma-and-multiple-hereditary-exostosis