Feeling a lump inside the sole of foot can be concerning, especially if it causes pain while walking. One of the most common causes of such a lump is a plantar fibroma, a benign thickening of the top layer of the plantar fascia. However, other conditions can also cause nodules or swelling in this area, so a thorough assessment is essential. So, what causes a lump inside the sole of foot, with a focus on plantar fibroma, and how do we treat this condition? 

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 are not cancerous and typically grow slowly, but they can become uncomfortable over time, particularly when walking barefoot. It can occur in both feet in 25% of cases. 

The exact cause is not always clear. Genetics, foot trauma, diabetes and repetitive strain may contribute. The condition is more common in middle-aged adults and has been linked to Ledderhose disease, which is similar to Dupuytren’s contracture in the hand.

Assessment of Lump Inside the Sole of Foot

People with a plantar fibroma usually notice a firm lump in the sole of the foot, most commonly in the arch, which may be tender or painless. The size can vary, and the lump is often fixed to the underlying fascia, making it less mobile under the skin. In some cases, more than one fibroma may develop (a condition known as plantar fibromatosis).

While the lump may not initially cause discomfort, it can become problematic when it presses against footwear. Pain may increase during prolonged walking, running, or standing on hard surfaces.

A sports doctor will examine the lump’s size, location, and consistency during an assessment. Plantar fibromas are typically firm, non-mobile, and deep-seated. They are often visible. The overlying skin is usually normal, with no signs of infection.

Other Possible Causes of a Lump Inside the Sole of Foot

It’s essential to consider these in the differential diagnosis:

Imaging and Diagnosis for a Lump Inside the Sole of Foot

Imaging is often required to confirm the diagnosis of a plantar fibroma and to rule out other possible causes. Ultrasound is a quick and effective way to visualise the fibroma within the plantar fascia. It typically appears as a mix of grey colours and a well-defined mass embedded in the plantar fascia with increased blood flow. 

MRI provides a more detailed assessment, especially in complex or uncertain cases. It is also critical to rule out cancer.

Treatment Options for Plantar Fibroma

Treatment for plantar fibroma depends on the size of the lump, the severity of symptoms, and the impact on daily activities. Most cases are managed with simple treatments. 

Simple Treatments 

In cases with mild pain, observation and simple measures may be all that’s needed. Wearing supportive footwear with cushioned soles and arch support can help offload pressure from the lump. Custom orthotics with a cut-out or soft pad over the fibroma can reduce discomfort during walking.

Anti-inflammatory medications can be used short-term to ease pain, although the fibroma is not inflammatory.

Some doctors use shockwave therapy to reduce pain, although studies on effectiveness are limited. 

An ultrasound-guided corticosteroid injection may sometimes reduce pain or temporarily shrink the fibroma. However, results are variable, and the fibroma often returns to its original size. Steroid injections carry a small risk of rupturing the plantar fascia, so this approach should be used with caution. Colleganese injections have been used with mixed results. 

Surgical Management

Surgery is considered when the fibroma is large, painful, or not responding to conservative treatment. The procedure involves excising the fibroma, but a full plantar fasciectomy is sometimes required to reduce the risk of recurrence. Recovery can be prolonged, and complications such as arch collapse or scar sensitivity can occur. Therefore, surgery is usually reserved when simple treatments have failed. 

Final Word from Sportdoctorlondon about a Lump Inside the Sole of Foot

A lump inside the sole of foot is often due to a plantar fibroma, a benign fibrous nodule that forms within the plantar fascia. While it may be painless initially, it can lead to discomfort, especially with prolonged walking or wearing tight footwear. Assessment by a clinician, supported by imaging such as ultrasound or MRI, helps confirm the diagnosis and rule out other causes such as cysts, lipomas, or more serious lesions. Treatment is usually conservative, focusing on offloading the area and managing symptoms. In more advanced cases, guided injections or surgery may be considered.