Bone Swelling on the Big Toe

David Tollafield

Mar 184 min read

the edge of the nail may lift. — The nail may lift at one corner.

Bone Swellings called Sub-Ungual Exostosis

Curious shapes, distortions and nail problems are always fascinating to podiatrists and can be associated with bone swellings, often called sub-ungual exostoses. The distortion of the end of the toe and callus formation in some of my patients was not uncommon, and I had to treat this together with what we call the nail apparatus. The term collectively involves the nail bed. A red, hard swelling was evident in young patients, usually under 30 years of age, where the nail was often thin and heavily distorted.

If your swelling looks suspicious, it doesn't mean it's malignant!

As the lesion progresses the toe looks strange — More extensive distortion is often associated with an osteochondroma.

Exostosis is an abnormal outgrowth of bone, while sub (under) and ungual imply the tip of the toe. Ungulates such as horses walk on the tips of their toes, and their nails have adapted into a single bone and toenail, the keratinised hoof.

There is a dearth of material from some of the formal UK sites, but the NHS and Wye Valley NHS Trust have written a specific guide sheet available to download here (guide sheet) checked 23/1/25. When it comes to factsheets and guides, one certainly finds great variations, and there is no doubt if you perform a search, you will find more information, often from the USA. Dermatology Advisor is useful.

What is bone swelling, and why is it confusing?

The condition seems to be limited to the young because of the immature cells involved. We know that cartilage cells (chondrocytes) can change to bone cells (osteocytes) as part of growth development. Chondrocytes are the soft material that you find on the ends of bone joints with raw meat and chickens.

An injury to the toe is common, not least because the toe sticks out at the end of the body. The excessive growth, like skin growth (hypergranulation) in an ingrown toenail, confuses the clinician because the skin is shiny, stretched, red and easily knocked. Bone samples sent off show malignancy in less than 5% of cases overall, and in the foot, this is even rarer.

My youngest patient was 10 years old, and the average patient was probably around 19-20, with the oldest osteochondroma at 35 years. I have seen pseudo-exostoses and little spikes in all ages, but the subungual osteochondroma forms thickened skin that looks odd, as it has blood vessels running through.

The raised nail edge can be caused by the end of the toe bone sticking out with cartilage capping over the end. Illustration A shows the nail-distorting type of exostosis, or subungual projection, distorting the nail, while B shows the smaller phalanx of a lesser toe projecting abnormally forward. As the toe appears longer, the suspicion of bony outgrowth should be raised. The red areas indicate stretched skin, and in the case of A, the nail may appear soft, thin, and moulded.

Subungual exostoses form different bone projections. — There are two scenarios. Subungual exostoses are often associated with osteochondroma. The nail is blue, the skin is stretched red, and the bone is pinky-orange.

Planning & Treatment

An X-ray confirms bone but not cartilage. Resist cutting the area as if it were an excess nail, as the skin will bleed easily. A healthy suspicion of cartilage must be considered in younger age groups. A biopsy (sample specimen) is not needed if surgery is being performed, as radical excision (cutting out) is necessary, with nail bed repair afterwards.

More often, the nail returns only slightly damaged after surgery, but all patients must be made aware that the nail may be permanently thickened, discoloured, or distorted. Permanent removal can deal with this later. Guide sheets, such as the one produced by the Wye Valley podiatric surgery department, will inform patients what to expect and how to best recover after surgery.

For the patient, any swelling should be examined by a professional if it is slow-growing and no notable injury is attributed.
Wear open-toed footwear until you can see someone or as deep-toe boxed shoes as possible. Soft uppers might be better to avoid pressure.
For the podiatrist or GP. Take an X-ray if suspicious and act upon the findings.
The lesions are rarely malignant but should be treated with moderate urgency to seek an early diagnosis from an excisional biopsy.
All surgical treatments should come with a fact sheet and a post-operative guide.
Surgery is suited to local anaesthetic management in appropriate facilities.
Histology is always advised with this osteochondral lesion, but such decisions will be based on the surgeon's experience and local policy.

Should any other specialists see a patient? This will depend on your local area; those who have appropriate training and experience in foot surgery are the people to discuss treatment with. If in doubt, speak to your GP about referral.

David's book, which covers an introduction to feet popular among lay readers and students, offers more about feet. Buy it now from Amazon books.