Subungual hyperkeratosis

Subungual hyperkeratosis (exostoses)

Description, Causes and Risk Factors:

The terms subungual refers to something that is underneath the nail on the toes or fingers. The term exostosis refers to an overgrowth of bone. This can also be called a bone tumor. The great majority of which are benign. So a subungual exostosis is an overgrowth of bone underneath the nail. These overgrowths of bone are usually very small but can be painful when walking or wearing tight shoe gear.

Subungual hyperkeratosis

The subungual exostoses can also cause deformity in the nails. When the bone grows directly towards the nail and disrupts the nail bed, the nail itself will grow in a deformed manner. The nail usually appears to have a ridge in it. In some cases even if the exostosis is removed the damage to the bed of the nail persists leaving the ridge in the nail.

A subungual exostosis is a benign bone growth which often arises from the distal tuft of the distal phalanx and grows dorsally, often disturbing the nail plate and causing pain. Another lesion which presents, in the same manner, is a subungual osteochondroma. In some texts these terms are used interchangeably. The principal differences between these two entities are the histopathologic findings and prognosis following treatment. In addition, rare instances of a subungual osteochondroma differentiating to an osteochondrosarcoma have been reported. Both of these conditions present with the same symptoms and will, therefore, be reviewed together.

The specific etiology of these diseases is unknown. In general, trauma and infection appear to play a role in the pathogenesis of both the subungual exostosis and subungual osteochondroma. Some feel that a subungual osteochondroma is congenital in origin. The majority of cases reported in the literature which occur in the foot have a history of either direct trauma or chronic irritation.

At the present time, there have been over 300 cases reported in the literature. These include both the subungual exostosis and subungual osteochondroma.


Initially, in typical cases, a small firm lesion appears which is usually located deep in the free edge of the nail. Pain, particularly severe on walking, develops due to the collision of the nail plate with the expanding exostosis. The overlying nail is pushed up and is finally detached, leaving a mass of fibrous tissue whose surface may become eroded and infected. This mass overlies the exostosis.


Your Podiatrist can examine the nail and decide what course of action is best. Depending on the condition he/she may decide to have X-rays taken.


A number of treatment modalities have been reported in the literature, including radiation, cauterization, curettage of the lesion, partial phalangectomy, phalangectomy, and digital amputation. Excision of the lesion with adequate removal of the osteochondral cap is considered the treatment of choice, providing the best overall success rate with the least amount of destruction of normal anatomy.

A variety of surgical procedures have been described for the excision of a subungual exostosis. Although three approaches have been detailed below, they are merely variations of a common theme. The open methods of dissection provide direct visualization of the phalanx, and facilitate procurement of a specimen of bone for diagnostic study.

Treatment 1. Partial or total nail avulsion can be performed, followed by a linear incision of the nail bed. Excision of the exostosis is then performed with hand instrumentation, followed by curettage of the distal phalanx.

  • Treatment 2. A transverse incision is placed at the distal tip of the digit with excision of the exostosis and possible excision of the distal aspect of the distal phalanx. Removal of the nail may not be necessary for this procedure.
  • Treatment 3. Minimal dissection is used through a small transverse incision at the tip of the digit. The protuberance of bone is then curetted or hand rasped prior to lavage and closure.

NOTE: The above information is for the educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


  1. Elizabeth Taylor

    I feel i have gotten to the bottem of my toenail problem and i can go to the doctor with confidence and knowledge of what the next steps should be to fix the problem. Thankyou for your help

    • editor-m

      Thank you for your comment. Looking forward to hearing from you after the visit.


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