What is Morton’s Neuroma?
Morton’s neuroma is painful swelling, irritation or damage of the nerves leading to the toes. Irritation of the nerves generates sharp burning pain in the ball of foot and a sensation as if one is standing on a pebble or a fold in the sock. Most commonly the nerve running between the third and fourth toe (third interdigital nerve) is involved. In as many as 28% of cases adjacent nerves may also be involved (commonly the second interdigital nerve and rarely the first and fourth interdigital nerves).
This condition is addressed by many other names including Morton’s metatarsalgia, Morton’s entrapment, interdigital neuralgia/ neuritis/ neuroma and interdigital nerve compression syndrome.
What are The Symptoms of Morton’s Neuroma?
This condition is most commonly seen in middle aged women. Women are 5-10 times more likely to be affected as compared to men. Common symptoms of Morton’s Neuralgia include
- Burning or sharp forefoot pain in between the toes. Initially the pain may be present only when wearing tight/heeled shoes and on prolonged walking or standing. Chronic cases may develop constant rest pain and night pain. The pain can radiate to toes or occasionally to the dorsal aspect of the foot or even the lower leg.
- Feeling like there is a “bunched-up sock” or a pebble under the ball of the foot is present in more than 50% of patients
- Numbness and/or tingling in the third and fourth digits or in between the toes
- Local tenderness and clicking sensation
Why Does it Occur?
This condition is linked to
- Wearing tight, pointy or high-heeled shoes as this can place extra pressure on the forefoot.
- People with flat feet, high arches, or abnormal toe position as seen with deformities such as bunions, hammer toes.
- High-impact athletic activities such as jogging, running, tennis and other racquet sports, rock climbing, snow skiing may subject feet to repetitive trauma.
A combination of anatomical and biomechanical factors is thought to contribute to the development of Morton’s Neuroma. Third interspace is commonly affected as this a narrower space with greater mobility of the 4th metatarsal relative to the 3rd metatarsal, producing a greater shearing force and trauma. The third digital nerve has increased thickness and is tethered in the third web space making it more susceptible. The compression and repetitive trauma to the nerve results in blood supply changes, nerve oedema/ degeneration, and excessive fibrosis (scarring) around the nerve.
Biomechanically wearing pointed, high- heeled shoes raises the body’s centre of gravity, reduces the support base of the weight bearing foot and produces extension at some of the foot joints predisposing the nerves to compression.
How is Morton’s Neuroma Diagnosed?
Diagnosis is usually made through history, clinical examination and is aided by imaging (ultrasonography, magnetic resonance imaging). Presentation features have already been discussed in the previous section. Examination involves specific tests such as the thumb index finger squeeze test (pain on applying pressure in the intermetatarsal space with thumb placed on the dorsal aspect whereas index finger is kept on the plantar aspect), Mulder’s click test and foot squeeze test.
Ultrasound and magnetic resonance imaging can help in confirming the diagnosis and give information about the location, number, and size of neuroma. A neuroma of >5mm size on MRI is generally significant. An x ray may show outward deviation of the toe (Sullivan’s sign) and a faint shadow in case of a large Morton’s neuroma.
How is Morton’s Neuroma Treated?
The treatment options for Morton’s Neuroma include
Footwear Modification
Wearing a wide, soft-soled, laced shoe with a low heel is helpful in relieving pressure on the nerve. Modifications to footwear have been shown to improve symptoms in up to 41% of patients but are associated with lower satisfaction rates when compared with steroid injections.
Orthotics
Metatarsal bar or a soft metatarsal support spread across the metatarsal heads. This insole relieves pressure on the neuroma and thus improves symptoms.
Medications
A combination of different types of medications, including Anti-inflammatory and neuropathic agents is used to reduce pain.
Ultrasound Guided Steroid Injections
Steroid injections are one of the most commonly used methods of nonoperative treatment. Several studies have purported that ultrasound (US) added accuracy to the injection procedure and one study demonstrated more pain reduction with ultrasound guided injections compared to the unguided injections. One study indicated at least 9 month relief in combination with physical therapy and these injections are more effective if used within one year of onset of symptoms. A dorsal approach (from the top of the foot) to the injection is associated with better outcomes and a lower risk of plantar fat pad atrophy and associated pain and gait disturbances. Some individuals may require multiple injections although a satisfactory outcome can be achieved in a majority (up to 82.4%). Some studies indicate that the size of neuroma may have an effect on the outcome of injections whereas others found no such relationship.
Given the actual problem and the mechanism of generation of neuroma PRP treatment is less likely to work in this condition and hence I do not offer this in Morton’s neuroma.
The treatment of the concomitant anatomical and functional disorders is important in the prevention of recurrence.
Cryotherapy
Cryotherapy or freezing of nerves can help reduce the pain in this condition. The treatment involves creating a freezer burn on the outer layer of the nerve to interrupt the pain signal being sent to the brain. A probe is placed next to the affected nerve and the temperature of the probe is then dropped to freeze the irritated nerve. The freezing inactivates the nerve producing pain relief.
Cryotherapy is a relatively safe and effective means of treating localized nerve irritation. In one study 4 out of 5 patients improved with this treatment.
Alcohol Nerve Injections
Alcohol and other similar chemicals are used to impair the nerve structure and functioning. One study reported complete symptom resolution in up to 89% of patients although multiple treatments are often required, and the effects diminish with time. The procedure complications may include peri-procedural pain (16.8%), allergic reaction (1.1%), and failure with up to 20% progressing to surgery. In one study approximately a third of patients experienced complications including burning pain (can sometimes last for weeks). The fibrosis associated with the treatment can make any subsequent surgery challenging.
Radiofrequency Ablation of Nerve
This procedure involves creating a heat lesion of the nerve to reduce the symptoms. It involves placing a special needle near the nerve under ultrasound guidance followed by creating heat lesion using the radiofrequency waves.
Physical Therapy
Intrinsic and extrinsic foot muscle strengthening to improve transverse arch and control foot pronation can help in addressing the biomechanical problems thereby reducing the chances of recurrences.
Surgery
It has been found to be effective and to elicit positive results in 80% to 90% of cases. One study however found the failure rate following surgical excision to be up to 30%. There are multiple reasons for this such as incomplete resection, multiple neuromas, recurrence or incorrect diagnosis.
