Morton's neuroma is more known as Morton's metatarsalgia, because it consists of a perineural fibrosis, neural degeneration and demyelination of the common digital nerve rather than the existence of a true neuroma. It often occurs in the third web space but can affect any. It is more common in females and has a peak incidence in the fifth decade.
The aetiology is unknown but the anatomical distribution supports a theory that it relates to a compression of the nerve where it passes between metatarsal heads and under the transverse intermetatarsal ligament.
This has lead to theories that activities squeezing the metatarsal heads together, such as wearing tight shoes or excessive toe dorsiflexion (for example from running or squatting) may cause the pathology to develop.
Alternatively, it may be an inflammatory change in an intermetatarsal bursa causing fibrosis around the nerve.
The condition is characterised by a sharp neuropathic pain at the level of the metatarsal heads shooting into adjacent toes. Weight-bearing and wearing shoes exacerbate it. Some describe a sensation of 'walking on a pebble' and relieve symptoms by foot massage.
Symptoms can be intermittent with long intervals and it tends to be progressive in both intensity and frequency.
Examination may be normal, or there may be tenderness over the nerve and diminished sensation. Pain is in the intermetarsal space rather than the plantar or dorsal aspects and a mass may be palpable.
Symptoms are reproduced with dorsoplantar compression of the web space while squeezing the metatarsal heads. This manoeuvre may produce an audible click, a 'Mulder click', thought to be the swelling moving dorsally between the metatarsals.
Clinical examination is the mainstay of diagnosis but occasionally ultrasound or MRI scanning is useful.
Metatarso-phalangeal (MTP) synovitis can be easily misdiagnosed as a Morton's neuroma. MTP synovitis produces pain at the joint which is exacerbated by forced flexion, and there may be joint swelling visible.
Careful palpation of the metatarsal joints, heads and shafts helps locate symptoms to distinguish other diagnoses such as stress fractures. Swelling of the second MTP joint may be early Freiburg osteochondrosis.
Hammertoes are usually distinguished by their appearance but can be mistaken in early development. Neuralgic pain produced by squeezing the metatarsal heads in two planes helps confirm a Morton's neuroma.
Other diagnoses such as neoplasms, ganglion cysts and true neuromas can be difficult to distinguish and, if symptoms are not typical, consider imaging.
Treatment includes avoiding aggravating footwear and shoe pads, which aim to elevate and separate adjacent metatarsal heads. NSAIDs are used to reduce pain and inflammation.
Steroid injections may help but adverse effects include plantar fascia pad necrosis and transient toe numbness. Ultrasound guidance allows a more accurate approach.
For persistent symptoms the nerve and surrounding tissue is excised, which usually relieves the pain but results in permanent toe numbness and loss of normal sweat production.
Post-surgery pain and dysthesia around the area can be due to an irritated nerve stump, which may develop into a neuroma. Other techniques include nerve transpositions and intermetatarsal ligament releases to decompress the area.
Dr Lackey is a GP in Tyne and Wear and Mr Sutton is a retired orthopaedic surgeon from Hexham