Subungual Exostosis & Subungual Osteochondroma
Subungual exostosis (SE) and subungual osteochondroma (SO) are two benign bony growths that arise from the last bone of a finger or toe, most often the big toe. Although they look almost identical clinically (a stone-hard lump pushing up the nail plate), they differ clearly in their biology and causes.
- Microscopic Features (Histopathology):
- Subungual exostosis (SE): a mass of trabecular (spongy) bone covered by a fibrocartilaginous cap. It is a reactive process of endochondral ossification driven by repeated trauma (for example in soccer players, runners or people who wear tight high heels).
- Subungual osteochondroma (SO): a true bone tumor with a cap of hyaline cartilage. It usually arises from leftover fragments of growth plate cartilage and is sometimes linked to the inherited condition multiple hereditary exostoses.
- How They Damage the Nail:
- Unlike soft tumors (glomus tumors, myxoid cysts), SE and SO are stony-hard nodules. As the bone grows from the tip of the digit, it pushes straight upward through the nail bed tissue.
- This pressure lifts the nail plate away from the nail bed (onycholysis) or curves it into a pincer shape (pincer nail deformity). In later stages, the growth can break through the nail bed, causing a weeping ulcer and secondary infection.
People with an exostosis or osteochondroma often assume (or are told at non-specialist clinics) that they have an ingrown nail, nail fungus or a hard wart. Cutting the nail back deeply, using antifungal creams or CO2 laser burning does not address the cause and raises the risk of bone infection (osteomyelitis). At Haute-Derma, a lateral X-ray is the essential gold-standard test, followed by microsurgical bone shaving (osteophytectomy) to remove the root cause while preserving the appearance of the nail.
Clinical Features and X-Ray Criteria
These growths are most common in teenagers and young adults (typically aged 10–30), and the big toe (hallux) is by far the most frequent site.
Typical Clinical Signs
- Stony-hard subungual nodule: the lump feels firm like bone and does not move. If it has broken through the nail bed, its surface is often covered by a thick keratin crust.
- Pain with pressure: severe pain in tight shoes or when the nail is pressed firmly from above. Unlike a glomus tumor, the pain is not sharp and spontaneous and is not triggered by cold.
- Nail plate deformity:
- Localized lifting of the nail plate (onycholysis).
- A raised, beak-shaped or pincer-shaped nail plate.
- An ulcerated nail bed that often oozes yellow pus if infected.
Gold-Standard Diagnosis: Frontal and Lateral X-Rays Plus Ultrasound
- Lateral radiograph: the single most important diagnostic test. The X-ray clearly shows a radiopaque bony outgrowth attached to the top (dorsal) surface of the distal phalanx, with a trabecular pattern continuous with the normal bone.
- High-frequency ultrasound: shows the anechoic cartilage cap sitting on top of the bony growth, which X-rays cannot see. This cap is the part that must be removed most thoroughly during surgery.
Diagnosis, Bone-Shaving Surgery and Reconstruction at Haute-Derma
At Haute-Derma, subungual exostosis and osteochondroma are usually treated in a single procedure using our microsurgical cartilage-cap excision and distal phalanx bone-shaving protocol (Haute-Derma Osteophytectomy Protocol):
Imaging the Bone and Cartilage
- A lateral X-ray of the digit is required to measure the width of the base of the bony growth. Ultrasound is added to map the soft tissue margins and the overlying cartilage cap.
Nail Bed-Sparing Surgical Approach
- A digital block with 2% lidocaine and a tourniquet at the base of the toe or finger keep the surgical field clear.
- Rather than removing the whole nail plate, the doctor lifts back only the part of the nail directly over the growth.
- A straight longitudinal incision or an L-shaped incision is made in the part of the nail bed the growth has pierced, and the tissue is gently eased aside to expose the bony growth with its ivory-white to bluish-gray cartilage cap.
Cartilage Cap Excision and Bone Shaving (Osteophytectomy / Bone Curettage)
- Key principle: the entire cartilage cap must be removed, because it contains the cells that keep forming bone. If only the bone surface is scraped and the cap is left behind, the growth comes back quickly.
- A fine bone rongeur or a low-speed dental burr shaves the bony growth down to the normal cortical bone of the distal phalanx. The cut surface is filed perfectly smooth so it will not tear the nail bed later.
Microsurgical Nail Bed Repair
- Surrounding inflamed tissue is cleaned away and the nail bed is closed with ultra-fine 8-0 microsutures.
- An HPCH polymer biofilm is applied, a protective splint is placed and LLLT (630 nm) is given. The nail then gradually regrows, gliding over a smooth, flat nail bed without being lifted or deformed.
