Feeling a lump inside the sole of your foot can be worrying, especially if it hurts when you walk. The most common cause of a lump in the sole or arch is a plantar fibroma — a benign thickening of the plantar fascia. But other conditions can cause nodules or swelling here, too, so a proper assessment matters. So what causes a lump inside the sole of the foot, and how do we treat a plantar fibroma?

(If your lump is on the side or outer edge of your foot rather than the sole, see our page on a lump on the side of the foot.)

What is a plantar fibroma?

A plantar fibroma is a benign fibrous nodule that forms within the top of the plantar fascia, usually on the inner side of the sole. Plantar fibromas aren’t cancerous and typically grow slowly, but they can become uncomfortable over time, particularly when walking barefoot. They occur in both feet in about 25% of cases.

The exact cause isn’t always clear — genetics, foot trauma, diabetes, and repetitive strain may all contribute. The condition is more common in middle-aged adults and is linked to Ledderhose disease (plantar fibromatosis), which is similar to Dupuytren’s contracture in the hand.

Assessing a lump inside the sole of the foot

People with a plantar fibroma usually notice a firm lump in the sole, most often in the arch, which may be tender or painless. The size varies, and the lump is often fixed to the underlying fascia, making it less mobile under the skin. Sometimes more than one fibroma develops — a condition known as plantar fibromatosis.

The lump may not hurt at first, but it can become a problem when it presses against footwear, with pain increasing during prolonged walking, running, or standing on hard surfaces.

On examination, a sports doctor assesses the lump’s size, location, and consistency. Plantar fibromas are typically firm, non-mobile, and deep-seated, often visible, with normal overlying skin and no signs of infection.

Other possible causes of a lump inside the sole of the foot

These need to be considered in the differential diagnosis:

Imaging and diagnosis

Imaging usually confirms a plantar fibroma and rules out other causes. Ultrasound is a quick, effective way to see the fibroma within the plantar fascia — it appears as a well-defined mass embedded in the fascia, often with increased blood flow. MRI provides more detail in complex or uncertain cases, and is important for excluding a tumour.

Treatment options for a plantar fibroma

Treatment depends on the size of the lump, the severity of symptoms, and the effect on daily life. Most cases are managed simply.

Simple treatments

For mild symptoms, observation and simple measures are often enough. Supportive footwear with a cushioned sole and arch support offloads the lump, and custom orthotics with a cutout or a soft pad over the fibroma reduce pressure during walking. Anti-inflammatory medication can ease pain in the short term, though the fibroma isn’t inflammatory. Some doctors use shockwave therapy to reduce pain, though the evidence is limited.

An ultrasound-guided corticosteroid injection may sometimes reduce pain or temporarily shrink the fibroma — but results are variable, and the fibroma often returns to its original size. A steroid injection carries a small risk of rupturing the plantar fascia, so it’s used with caution. Collagenase injections have also been tried, with mixed results.

Surgery

Surgery is considered when the fibroma is large, painful, or unresponsive to conservative treatment. It involves excising the fibroma, though a more extensive plantar fasciectomy may be needed to reduce the high risk of recurrence. Recovery can be prolonged, and complications such as arch collapse or scar sensitivity can occur — so surgery is reserved for when simpler treatments have failed.

Frequently asked questions about a lump inside the sole of the foot

Is a lump in the sole of my foot always a plantar fibroma?

It’s the commonest cause, but not the only one. Ganglion and epidermoid cysts, lipomas, a plantar fascia rupture, and (rarely) tumours can also present as a sole lump. That’s why imaging — usually ultrasound — is used to confirm a fibroma and rule out other causes.

Are plantar fibromas dangerous?

No — they’re benign and don’t turn cancerous. The concern is discomfort and pressure when walking rather than any serious risk. Imaging is still worthwhile for confirming the diagnosis and excluding rarer lumps.

Will a plantar fibroma go away on its own?

Usually not — fibromas tend to persist and can slowly enlarge. Many stay comfortable with the right footwear and orthotics, so they don’t always need active treatment, but they don’t typically disappear.

Should I have surgery for a plantar fibroma?

Usually not as a first step. Surgery has a high recurrence rate and a slow recovery, so it’s reserved for large or painful fibromas that haven’t responded to footwear, orthotics, and other simple measures.

What’s the difference between a plantar fibroma and plantar fasciitis?

A plantar fibroma is a lump in the arch; plantar fasciitis is inflammation of the plantar fascia, causing heel pain, without a lump. They’re different problems, though both involve the plantar fascia.

Is a lump on the sole the same as one on the side of the foot?

No. A lump on the side of the foot is more often a bony prominence, cyst, or other cause — see our page on a lump on the side of the foot.

Final word from Sport Doctor London about a lump inside the sole of the foot

A lump inside the sole of the foot is most often a plantar fibroma — a benign nodule in the plantar fascia. It may be painless at first, but it can become uncomfortable with prolonged walking or tight footwear. Assessment with ultrasound or MRI confirms the diagnosis and excludes other causes such as cysts, lipomas, or rarer lesions. Treatment is usually conservative — offloading the lump and managing symptoms — with injections or surgery reserved for advanced cases.

To book a foot assessment with Dr Masci in London, contact the team here or call +44 (0) 203 488 0350.

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