Morton's neuroma

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Morton's neuroma (also known as Morton's metatarsalgia, Morton's neuralgia, plantar neuroma and intermetatarsal neuroma) is a benign neuroma of the interdigital plantar nerve.

This problem is characterised by numbness and pain, relieved by removing footwear.

Although it is labeled a "neuroma", many sources do not consider it a true tumor, but rather a thickening of existing tissue.

Symptoms and signs

Symptoms include: pain on weight bearing, frequently after only a short time; the pain is felt as a shooting pain affecting the contiguous halves of two toes. Burning, numbness and parasthesia may also be experienced. Classically the 3rd digital space between the 3rd and 4th toes is affected, but the condition can occasionally occur in the 2nd and 3rd interdigital space. The pain is caused by pressure on the enlarged section of nerve where it passes between the metatarsal heads, and is squeezed between them. The first toe is usually not involved. Neuroma in the 4th/5th interdigital space is described, but is extremely rare.

Negative signs include no obvious deformities, erythema, signs of inflammation or limitation of movement. Direct pressure between the metatarsal heads will replicate the symptoms, as will compression of the forefoot between the finger and thumb so as to compress the transverse arch of the foot. This is referred to as Mulder’s Sign.

There are other causes of pain in the forefoot. Too often all forefoot pain is categorized as neuroma. Other conditions to consider are capsulitis, which is an inflammation of ligaments that surrounds two bones, at the level of the joint. In this case it would the ligaments that attach the toe bone to the metatarsal bone. Inflammation from this condition will put pressure on an otherwise healthy nerve and give neuroma type symptoms. Additionally, an intermetatarsal bursitis between the third and fourth metatarsal bones will also give neuroma type symptoms because it too puts pressure on the nerve.

Since a neuroma is a soft tissue condition an MRI should be helpful in diagnosis, however, often an MRI will be inconclusive for neuroma even though a neuroma exists.

Treatment

Serveral differnt methods are used for the treatment of Morton's neuroma. Hughes et al., demonstarted that an 84% cure rate could be established by sonographically guided alcohol injections into the lesion.2 While the injection of alcohol seems promising, the injection of steroids only produced short term results.1 Endoscopic decompression yeilded the best results, as 92.5% of the patients were cured of pain.4


References

  1. Hassouna H, Singh D, Taylor H, Johnson S. "Ultrasound guided steroid injection in the treatment of interdigital neuralgia." Acta Orthop Belg. 2007 Apr;73(2):224-9.
  2. Hughes RJ, Ali K, Jones H, Kendall S, Connell DA. Treatment of Morton's neuroma with alcohol injection under sonographic guidance: follow-up of 101 cases. AJR Am J Roentgenol. 2007 Jun;188(6):1535-9.
  3. Mulder, JD. "The causative mechanism in morton's metatarsalgia." J Bone Joint Surg. 1951;33B:94-95.
  4. Shapiro SL. "Endoscopic decompression of the intermetatarsal nerve for Morton's neuroma." Foot Ankle Clin. 2004 Jun;9(2):297-304
  5. Zelent ME, Kane RM, Neese DJ, Lockner WB. "Minimally invasive Morton's intermetatarsal neuroma decompression." Foot Ankle Int. 200;28(2):263-5.

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