Morton neuroma (interdigital neuroma), first described in 1876, is a perineural fibrosis and nerve degeneration of the common digital nerve. Morton neuroma, or Morton's neuroma, is not a true neuroma, although it results in neuropathic pain in the distribution of the interdigital nerve secondary to repetitive irritation of the nerve. The most frequent location is between the third and fourth metatarsals (third webspace). Other, less common locations are between the second and third metatarsals (second webspace) and, rarely, between the first and second (first webspace) or fourth and fifth (fourth webspace) metatarsals.
Pronation of the foot can cause the metatarsal heads to rotate slightly and pinch the nerve running between the metatarsal heads. This chronic pinching can make the nerve sheath enlarge. As it enlarges it than becomes more squeezed and increasingly troublesome. Tight shoes, shoes with little room for the forefoot, pointy toeboxes can all make this problem more painful. Walking barefoot may also be painful, since the foot may be functioning in an over-pronated position.
Symptoms of interdigital neuroma typically manifest as a sharp, burning or tingling sensation in the forefoot. The pain radiates toward the lesser toes and is aggravated by shoe wear. The pain is relieved when the shoe is removed and the forefoot is massaged. Sometimes the symptoms involve specific toes.
The doctor will ask about your symptoms and medical history. A physical exam will be done. Initial diagnosis of Morton's neuroma is based on your description of the type and location of pain and discomfort in the foot. The diagnosis will be confirmed by a physical exam of the foot, including checking for mechanical abnormalities in the foot, squeezing the side of the foot, which will usually cause pain when Morton's neuroma is present. Examination of your shoes to check for excess wear in parts of the shoe, check to see whether the shoes are too tight. Imaging tests evaluate the foot and surrounding structures. This may be done with X-ray, MRI scan, Ultrasound. Injections of local anesthetic can also be used for diagnosis.
Non Surgical Treatment
Sclerosing alcohol injections are an increasingly available treatment alternative if the above management approaches fail. Dilute alcohol (4%) is injected directly into the area of the neuroma, causing toxicity to the fibrous nerve tissue. Frequently, treatment must be performed 2-4 times, with 1-3 weeks between interventions. An 60-80% success rate has been achieved in clinical studies, equal to or exceeding the success rate for surgical neurectomy with fewer risks and less significant recovery. If done with more concentrated alcohol under ultrasound guidance, the success rate is considerably higher and fewer repeat procedures are needed. Radio Frequency Ablation is also used in the treatment of Morton's Neuroma The outcomes appear to be equally or more reliable than alcohol injections especially if the procedure is done under ultrasound guidance.
About one person in four will not require any surgery for Morton's neuroma and their symptoms can be controlled with footwear modification and steroid/local anaesthetic injections. Of those who choose to have surgery, about three out of four will have good results with relief of their symptoms. Recurrent or persisting (chronic) symptoms can occur after surgery. Sometimes, decompression of the nerve may have been incomplete or the nerve may just remain 'irritable'. In those who have had cutting out (resection) of the nerve (neurectomy), a recurrent or 'stump' neuroma may develop in any nerve tissue that was left behind. This can sometimes be more painful than the original condition.
Women, particularly those who wear tight shoes, are at greatest risk for Morton?s neuroma. The best way to prevent the condition is to wear shoes with wide toe boxes. Tight, pointed shoes squeeze bones, ligaments, muscles and nerves. High heels may worsen the problem by shifting your weight forward. Over time, this combination can cause the nerves to swell and become painful.