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What is a Subungual Exostosis?

Subungual Exostosis

A subungual exostosis is a benign tumor of bone and cartilage protruding near the tip of a toe or finger, just under or adjacent to the nail. It usually involves the big toe but can also involve other digits of the foot or hand.


The cause of subungual exostosis is unknown, however, the risk factors include:

  • Trauma
  • Chronic infection
  • Tumor
  • Hereditary abnormality
  • Activation of a cartilaginous cyst


Signs and symptoms of subungual exostosis include:

  • Firm lesion usually appearing under the inside edge of the big toenail
  • Pain with pressure
  • Deformity of the nail
  • the nail from the nail bed
  • Surrounding soft tissue inflammation or infection


Your doctor will make a diagnosis based on your symptoms, medical history, physical examination, and certain tests. During the physical examination, the appearance of the toe and nail are noted. X-rays or ultrasounds help identify the exostosis. The exostosis usually has a cap of fibrocartilage. Subungual exostosis can be categorized into:

  • Type-I or mild deformity: This is early subungual exostosis which may be associated with pain upon pressure and mild nail deformity and corn formation may be present, but the nail plate is intact.
  • Type-II or moderate deformity: The exostosis is present beyond the nail plate and may interfere with linear nail growth.
  • Type III: The exostosis is located under the nailbed. Its growth causes a pincer nail deformity (over curvature) and a variable degree of nail bed destruction with separation of the nail from the bed (onycholysis).
  • Type IV: Pain is palpated over the proximal nail fold. The nail folds are affected by non-healing granulation tissue.

Treatment for Subungual Exostosis

Treatments include:

  • Wearing a high box shoe which reduces pressure on the toes
  • Nail plate trimming/avulsion
  • Surgical removal: The outgrowth is surgically stripped off completely and the bone is cleanly scraped (curettage) to prevent future tumor development.
  • Surgery may also be needed to repair the nail bed.

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