What is Subungual Exostosis?

Subungual exostosis is a benign bony growth that develops beneath the nail (most often the big toe, less commonly fingers). The term “subungual” means “under the nail,” and “exostosis” refers to an outgrowth of bone. As the lesion enlarges, it pushes upward on the nail plate, causing pain, nail deformity, and sometimes infection.

Although noncancerous, it can be very uncomfortable and is often mistaken for other nail conditions.

Causes

The exact cause is not always clear, but contributing factors include:

  • Repeated trauma or irritation – stubbing the toe, dropping objects, or pressure from shoes

  • Previous infection – chronic ingrown toenails or nail bed infections

  • Genetic predisposition – some people are more prone to bony growths

  • Underlying syndromes – rarely, part of multiple hereditary exostoses

Symptoms

Patients with subungual exostosis typically notice:

  • A firm, painful lump beneath the nail

  • Nail changes – lifting, distortion, or separation (onycholysis)

  • Redness, swelling, or tenderness around the nail

  • Pain that worsens with shoes or pressure

  • Occasionally, ulceration or infection if the nail breaks down

Diagnosis

Diagnosis is usually straightforward with:

  • Physical exam – firm nodule under the nail, often tender

  • X‑rays – confirm the bony origin and rule out other tumors

  • Differential diagnosis – must be distinguished from warts, pyogenic granuloma, osteochondroma, glomus tumor, or even melanoma

Nonsurgical Treatment

Conservative care is limited, since the lesion is bony. Options may include:

  • Footwear modification – wider shoes to reduce pressure

  • Protective padding – to cushion the nail area

  • Nail trimming or thinning – to relieve pressure temporarily

These measures may ease discomfort but do not remove the growth.

When is Surgery Needed?

Surgery is the definitive treatment and is usually recommended when:

  • Pain is persistent

  • The nail is deformed or detached

  • The lesion continues to enlarge

  • Infection develops

Surgical excision involves removing the bony growth and curetting (scraping) the underlying bone to reduce recurrence. The procedure is typically done under local anesthesia (digital block).

Recurrence is uncommon if the lesion is completely removed. Nail appearance usually improves, though some deformity may remain if the nail bed was damaged.