Morton’s Neuroma | Intermetatarsal Bursitis
Morton’s neuroma is a compressive neuropathy of the interdigital nerve in the forefoot due to constant irritation at the plantar aspect of the transverse intermetatarsal ligament. It most commonly affects the 3rd webspace between the 3rd and 4th metatarsal heads, less commonly the 2nd webspace. Treatments for Morton’s neuroma – PubMed. It is the most common cause of metatarsalgia (pain in the ball of the foot), and it is the second most common compressive neuropathy after carpal tunnel syndrome. It is more prevalent in females (87.2 per 100,000 patients) than in males (50.2 per 100,000 patients) and is usually diagnosed in patients in the 4th through to the 6th decade of life Prevalence | Background information | Morton’s neuroma | CKS | NICE.
The exact etiological cause of Morton’s neuroma is still debated, with potential entrapment, ischemic and degenerative causes all being suggested Morton Neuroma – StatPearls – NCBI Bookshelf. The repeated compressive forces/mechanical microtraumas to the interdigital nerve ultimately lead to perineural fibrosis and subsequent symptoms. The relationship between foot posture index, ankle equinus, body mass index and intermetatarsal neuroma – PubMed. Intermetarsal bursitis is an inflammation of the intermetatarsal bursa, with evidence showing that this space-occupying lesion can be a contributing factor to the development of a neuroma due to local compression but can also be a standalone pathology in its own right. Diagnostic Considerations of Intermetatarsal Bursitis: A Systematic Review – PubMed.
Risk factors for developing a Morton’s neuroma is female sex, high BMI, tight-fitting shoes, systemic disease and foot biomechanics that lead to additional shearing forces through the forefoot. Study of the Anatomical Association between Morton’s Neuroma and the Space Inferior to the Deep Transverse Metatarsal Ligament Using Ultrasound – PMC
What are the signs and symptoms?
The most common symptom is pain, typically in the plantar aspect of the forefoot within the 3rd or 2nd webspace. Symptoms are aggravated by periods of ambulation and tight-fitting shoes. There may be associated paraesthesia/anaesthesia symptoms between the affected toes, and patients describe the sensation as walking on a stone or pebble. Morton’s interdigital neuroma: instructional review – PMC
Clinically there may be localised pain in the webspace with palpation; squeezing the metatarsal heads together may result in a Mulder’s sign, which is a painful, palpable click as the neuroma is displaced ventrally.
How is it diagnosed?
The diagnosis will be made from a combination of your clinical history, examination findings and, commonly, an ultrasound scan. The patients will have the signs and symptoms as discussed previously.
Ultrasound imaging is usually the first-line imaging modality to confirm the presence of a neuroma +/- intermetatarsal bursitis. It has been shown to have a strong sensitivity and specificity, with evidence supporting its superiority over MRI given its superior spatial resolution. The accuracy of ultrasonography and magnetic resonance imaging for the diagnosis of Morton’s neuroma: a systematic review – PubMed. MRI does remain useful, especially when patients have atypical features and to exclude different/concurrent pathology of the forefoot, such as bone stress injuries or, rarely, alternative space-occupying lesions.
The presence of a neuroma on imaging does not necessarily indicate cause. It is common for asymptomatic patients to have neuromas that cause no symptoms. Morton’s neuroma – Current concepts review – PMC. Furthermore, there is no clear correlation between the size of the neuroma and the severity of symptoms. The role of MRI and ultrasound imaging in Morton’s neuroma and the effect of size of lesion on symptoms – PubMed. Diagnosis, as always in musculoskeletal medicine, is made through imaging findings and clinical symptoms to help dictate appropriate treatment.
How is it treated?
Treatment options are divided into conservative and surgical.
Conservative options:
- Activity modification/change in footwear: sometimes these simple measures will allow things to settle. Wide-fitting shoes and avoiding high heels can reduce forefoot pressure.
- Orthotics/Metatarsal pads. When placed just proximal to the metatarsal heads, they can be helpful at reducing pressure through the forefoot, displacing pressure sites and making more room for the interdigital nerves. While a common and safe treatment option, there are no convincing results in large patient cohorts. The effectiveness of shoe modifications and orthotics in the conservative treatment of Civinini-Morton syndrome: state of art – PMC
- An ultrasound-guided steroid and local anaesthetic injection into the intermetatarsal bursa or around the entrapment site can provide short-term or medium-term relief or, in certain patients, be curative. Efficacy of Ultrasound-Guided Steroid Injections in the Management of Morton’s Neuroma: A Retrospective Cohort Study – PubMed There is still debate about which cohort of patients will respond more favourably to a steroid injection, but unsurprisingly, small Morton neuromas tend to have a better, longer-term outcome than larger ones. Morton’s neuroma – Current concepts review – PMC.
Surgical intervention:
For patients with refractory/reoccurring symptoms that have not responded to conservative options, surgical excision is usually definitive. Morton’s interdigital neuroma: a comprehensive treatment protocol – PubMed. There are both dorsal and plantar approaches possible; surgical options include neurectomy (nerve excision), which will leave a permanent numbness in the webspace, or decompression to relieve pressure on the nerve. The risk of decompression can include the reoccurrence of symptoms as tissues heal.
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