Who is most likely to develop Morton's neuroma?

It is more common in women than in men and mainly affects middle-aged women, with a reported female-to-male ratio of about five to one. Higher-risk groups include taekwondo competitors, ballet dancers, and runners.

What causes Morton's neuroma?

The exact cause is not clear. The most widely accepted idea is the chronic trauma theory: repeated dorsiflexion of the toes during walking causes chronic microtrauma and thickening of the interdigital nerve, so that the nerve becomes compressed beneath the transverse metatarsal ligament or by an inflamed intermetatarsal bursa.

What factors increase the risk of Morton's neuroma?

Common risk factors include wearing tight, narrow shoes, an overpronated foot type, toe deviation, bursal inflammation, thickening of the transverse metatarsal ligament, forefoot trauma, and high-impact sporting activity.

What symptoms does Morton's neuroma cause?

The typical symptoms are a burning sensation, stabbing pain, or an electric-shock-like tingling in the forefoot, and some patients describe it as feeling like walking on a stone. Standing, walking, or wearing tight, narrow shoes makes it worse, while resting and removing shoes may relieve it.

How does a physician assess Morton's neuroma on physical examination?

Pressing between the third or fourth metatarsal heads may reproduce pain, and squeezing the forefoot from the medial and lateral sides usually produces a marked click, known as Mulder's click. Some physicians will inject a diagnostic local anaesthetic to help confirm the diagnosis.

Morton's Neuroma: A Foot Pain to Watch For in Middle-Aged Women

Morton’s neuroma is a fibrotic, inflammatory process of an interdigital nerve in the foot, usually occurring between the third and fourth metatarsal heads, though it may also involve the second or fourth interspaces. The neuroma sits just before the nerve branches in the metatarsal region to supply the adjacent sides of two neighbouring toes, and it usually presents with one-sided symptoms.

Epidemiology

It is more common in women than in men and mainly affects middle-aged women, with a female-to-male ratio of about five to one.
Higher-risk athletes include taekwondo competitors, ballet dancers, and runners.
It is more common in the third interspace, which is narrower than the others. Because the nerve in the third interspace receives branches from both the medial and lateral plantar nerves, its increased thickness makes it more prone to compression and trauma.

Cause

The exact cause is not clear. The most widely accepted idea is the chronic trauma theory: the mechanical effect of walking causes chronic microtrauma to the interdigital nerve, and repeated dorsiflexion of the toes leads to nerve thickening. The resulting microtrauma compresses the nerve beneath the transverse metatarsal ligament or by an inflamed intermetatarsal bursa.
Repeated trauma leads to swelling of the plantar interdigital nerve, pathologically similar to other nerve entrapment syndromes.

Risk factors

Wearing tight, narrow shoes
An overpronated foot type
Toe deviation
Bursal inflammation
Thickening of the transverse metatarsal ligament
Forefoot trauma
High-impact sporting activity
Lipoma

Symptoms

Typical symptoms include forefoot pain that is a burning sensation, stabbing pain, or an electric-shock-like tingling. Some patients describe the feeling as walking on a stone or on marble.
Numbness between the toes appears in fewer than half of patients. With prolonged walking, the pain may radiate to the hindfoot or the leg and cause cramping.
The pain worsens with standing, walking, or wearing tight, narrow shoes.
Resting and removing shoes may relieve the pain.

Physical examination

Pressing between the third or fourth metatarsal heads may reproduce pain.
Squeezing the forefoot may produce radiating pain or abnormal sensations in the patient.
A snapping sound may be heard or felt, resulting from the nerve moving as it is squeezed.
On palpation of the affected area, compressing the forefoot from the medial and lateral sides usually produces a marked click or clicking sensation, commonly called Mulder’s click.
Some surgeons will inject a diagnostic local anaesthetic into the affected area to confirm the diagnosis, injecting up to 1 to 2 mL of anaesthetic.

Diagnosis

A clinical diagnosis can be made based on history and physical examination; X-ray is used mainly to rule out other causes.
Imaging such as ultrasound or MRI can help confirm the diagnosis.
Nerve conduction studies and electromyography may not be helpful.
Ultrasound may show thickening of the neuroma and, depending on the operator’s skill, may assess the nerve in more detail than MRI.

Treatment

Initial treatment includes changing footwear, choosing shoes with a wider toe box to reduce pressure on the nerve.
Rest, ice, and anti-inflammatory drugs (NSAIDs) can be used to reduce pain and inflammation.
Insoles or arch supports can also help reduce pressure and pain.
A local corticosteroid injection may help relieve symptoms, especially when conservative treatment has failed, though the effect may not be lasting.
- For an ultrasound-guided interdigital nerve injection, there are several injection paths; the usual consensus is to enter from the dorsal side to avoid plantar forefoot atrophy.
If the above measures fail to improve symptoms, surgical excision of the affected nerve may need to be considered, though surgical success rates vary.
The neuroma is excised through a dorsal or a plantar approach. The dorsal approach has fewer complications, because a plantar scar can cause pain.
A plantar incision is used mainly for recurrent neuromas or when there is a proximal local tender trigger point causing nerve pain; it lowers the rate of missed neuromas and does not require dividing the transverse metatarsal ligament. Its main drawback is that a painful plantar scar and plantar keratosis occur in about 5 percent of cases.
After surgery a special shoe is worn until the sutures are removed at about 7 to 14 days, with a compression wrap used for 2 to 6 weeks.

Prognosis

Most patients improve significantly with conservative treatment.
Patients may have persistent numbness after surgery, but the pain is usually markedly reduced.

Prevention

Wear loose shoes that fit the shape of the foot, and avoid high heels or overly tight shoes.
Change athletic shoes regularly to prevent overuse-related foot pressure.

References

Morton’s neuroma - Symptoms and causes - Mayo Clinic
Performing an Ultrasound Guided Morton’s Neuroma Injection - Sports Medicine Review (sportsmedreview.com)
Skeletal Radiol. 2021 Jul 14;51(3):581–586.
Foot Ankle Surg. 2018 Aug;24(4):271-281
Eur Radiol. 2019 Feb;29(2):620-627.