NB This page is from the 2005 Hyperbook.
Last evidence check May 2005.
Also known as Morton's metatarsalgia or Morton's neuroma, although Morton described neither (Morton thought this was a problem in the 4th MTP joint and Betts described the "neuroma" 70 years later).
The "neuroma" consists of degenerative and fibrotic changes in the common digital nerve near its bifurcation. However, there may be similar changes in adjacent unaffected nerves and it is not known why one becomes symptomatic. A number of causative factors have been suggested:
The symptoms may be quite non-specific:
Symptoms are commonest in the 3rd interdigital space, then the 2nd. Symptoms in the 4th space are rare and should make one doubt the diagnosis. Symptoms in the first space are virtually unknown.
The condition may remain undiagnosed for many years.
The diagnosis is often strongly suspected within the first minute of the consultation. However, it may be arrived as part of the assessment of a more generalised metatarsalgia, the details of which are found on the appropriate page. In any case, a full assessment of the foot should be carried out.
Ask about:
Examination should begin with assessment of any suggested nerve entrapment in the spine, proximal limb or tarsal tunnel.
The whole foot should be examined, looking for any other factors likely to produce metatarsalgia.
On local examination look for:
A local anaesthetic injection into the affected space may be useful - if it relieves the symptoms this is supportive of the diagnosis.
Both ultrasound and MRI have been described for imaging a neuroma, but the evidence for their value is not strong. However, if the clinical situation is atypical an ultrasound scan may be useful. If there is a suggestion of other forefoot pathology standing AP and lateral forefoot films should be obtained.
All patients should be advised on the use of shoes with adequate room in the toe-box and high heels should be avoided.
There is no proven role for orthoses.
If simple measures do not control the pain a steroid injection into the intermetatarsal space should be offered. The patient is warned that it may be quite painful for several days and they may need to rest more than usual. Also warn about the small risks of infection and cutaneous atrophy. The published results of this treatment are variable. Greenfield (1984) found that 90% of patients had little or no pain two years later, even if they got temporary or no benefit from the initial injection. Bennett (1995) found that about 50% of patients were relieved of pain by a single injection, the authors imply, but do not substantiate, that this result was maintained at follow-up 2.5-5 years later. Rasmussen, however, found that although 80% were relieved of pain by a single injection, 47% eventually had a neurectomy and most of the rest were symptomatic at review 2-6 years later.
If symptoms persist despite non-surgical treatment and the diagnosis is regarded as firm enough the patient may be offered an interdigital neurectomy.
We quote a success rate of 80% and warn patients that it may take several months to reach full benefit. We also warn them that a few patients may develop a new neuroma on the severed nerve end which may be more painful than the original problem.
The operation is done through a dorsal interdigital incision. Other surgeons prefer a plantar approach, and there is no evidence that one is better than the other. The nerve is divided 2-3cm proximal to the bifurcation and excised. The deep transverse metatarsal ligament may be partially released . The wound is closed with subcuticular Vicryl. Post-operatively the patient mobilises fully weight bearing.
Decompression of the interdigital space with excision of the bursa, division of the deep transverse metatarsal ligament and neurolysis of the common digital nerve has been reported. A randomised controlled trial against neurectomy would be helpful.