Abstract
A Morton's neuroma is a compressive neuropathy most commonly affecting the common digital nerve of the third inter-space. Symptoms are variable but usually the diagnosis can be made quite easily and the diagnosis is essentially a “clinical” one. When symptoms relate to the second inter-space the clinician needs to be alert to mechanical causes of metatarsalgia leading to secondary irritation of the nerve. Imaging with MRI scanning and/or ultrasound can be helpful but equally can be misleading, as there may be false positives and false negatives. In the case of ultrasound the accuracy of imaging depends on the experience and expertise of the radiologist.
Morton's neuroma surgery is usually associated with high levels of success but some reports suggest as many as 30% of patients under-going such surgery are dissatisfied with the outcome. The reasons for failed surgery can be broadly divided into three groups: a) wrong diagnosis b) wrong surgery and c) right diagnosis and right operation but unfavourable outcome. Wrong diagnosis is most commonly encountered in second space pathology when there is an underlying mechanical reason for the symptoms such as second MTP joint synovitis. This is usually secondary to joint overload associated with first ray insufficiency eg hallux valgus. This is the so-called Moron's neuroma. Wrong surgery occurs when the wrong space is operated upon, when mechanical causes are overlooked or when a plantar incision is made over the weight-bearing part of the forefoot, leading to painful scar formation. Wrong surgery can also involve failure to recognise anomalous anatomy within the space or insufficient nerve resection. Unfavourable outcomes include infection, stump neuroma formation or the onset of CRPS. Occasionally despite an appropriate assessment and operation a patient will derive no relief of symptoms and the cause of the pain remains totally unexplained.
Careful history and examination and careful pre-operative planning can reduce the incidence of failed Morton's neuroma surgery. The role of imaging is probably greater in such cases compared with those presenting with a primary Morton's neuroma but the diagnosis remains essentially clinical. Stump neuroma resection should be considered in patients presenting with repeat symptoms especially if there is initial surgical success followed by recurrent symptoms. If two explorations result in no success then a third exploration is unlikely to resolve the problem. Some patients are left with intractable symptoms and should be referred to a pain specialist, as further surgery often has nothing more to offer.
