Morton’s Neuroma

Morton`s neuroma is a perineural fibrosis and degenerative change of the common digital nerve in the forefoot, most commonly occurring in the third web space (between the third and fourth metatarsals). Despite the historical name "neuroma," it is not a true neoplasm but rather a reactive fibrotic change of the nerve and its surrounding tissues in response to chronic mechanical compression and irritation. It is a very common cause of forefoot pain in middle-aged women.

• Incidence: one of the most common forefoot conditions; predominately affects women (female:male ratio approximately 8:1); peak incidence 40–60 years; bilateral in approximately 15–20%; multiple interspace involvement in approximately 10%
• Most common web space: third web space (between 3rd and 4th metatarsal heads) — approximately 65–80% of cases; second web space approximately 20–30%; rarely first or fourth web space; the third web space is more susceptible because the common digital nerve in this space is larger (anastomosis between medial and lateral plantar nerves) and the intermetatarsal space is narrower
• Pathophysiology: nerve compressed between metatarsal heads during weight-bearing → repeated trauma → perineural fibrosis → epineural thickening → degenerative axonal change; the transverse intermetatarsal ligament (TIML) overlies the nerve and contributes to compression; narrow footwear and high heels increase compression
• Histology: perineural fibrosis, epineural thickening, axonal degeneration, and occasionally endarterial thickening — no neoplastic proliferation; the lesion is typically 5–10 mm in diameter

• Classic presentation: burning, sharp, electric, or cramping pain in the forefoot radiating to the toes of the affected web space; worsened by narrow shoes and high heels; relieved by removing shoes and massaging the foot; patients often describe the sensation of "walking on a pebble" or "something bunched in the sock"
• Tingling and numbness in the adjacent toes (between the third and fourth toes for third web space neuroma) in approximately 50%
• Pain worsens with prolonged standing and walking; relieved by rest and removing footwear
• Mulder`s click test: the most specific clinical test — examiner squeezes the forefoot in the mediolateral direction (compresses the metatarsal heads together) with one hand while the other hand applies dorsal-to-plantar pressure over the web space; a palpable click (Mulder`s click) with reproduction of the patient`s pain = positive; sensitivity approximately 60%, specificity approximately 85%
• Web space tenderness: direct plantar palpation between the metatarsal heads in the affected web space reproduces pain; more sensitive than Mulder`s test but less specific
• Web space pain with toe separation (Gauthier test): dorsal compression of the web space with passive toe separation; positive if pain reproduced

• Diagnosis is primarily clinical — the combination of typical symptoms + Mulder`s sign + web space tenderness has good diagnostic accuracy; imaging performed to confirm or when diagnosis uncertain
• Ultrasound (USS): imaging of choice for Morton`s neuroma — real-time dynamic assessment; identifies the hypoechoic nerve mass in the web space; dimensions measured; sensitivity 79–95%, specificity 78–99%; USS-guided injection can be performed simultaneously for diagnostic and therapeutic purposes
• MRI: confirms the lesion (low T1, low-intermediate T2 signal in the web space); useful when USS equivocal or when multiple web spaces are involved; shows bursal component if present; not routinely required for straightforward cases
• Weight-bearing foot radiographs: exclude metatarsal stress fracture, Freiberg`s infraction, and other bony pathology; do not visualise the neuroma itself
• Neuroma size on imaging: lesions <5 mm may not require surgery; lesions >6–8 mm are associated with poorer response to conservative management and injection; lesion size alone does not determine treatment — clinical symptoms guide management

• Footwear modification: wide toe box, low heel, well-padded forefoot — most important first step; eliminates extrinsic compression; highly effective in early disease
• Metatarsal dome pad: placed proximal to the metatarsal heads; redistributes forefoot load and spreads the metatarsals; reduces interdigital nerve compression
• Corticosteroid injection: USS-guided dorsal or plantar approach into the affected web space; approximately 50–70% of patients achieve significant short-term relief (6 months); long-term success (2+ years) in approximately 20–30%; repeat injection (up to 3 series) may be performed; risk of fat pad atrophy and skin depigmentation with repeated plantar injections
• Alcohol sclerosant injection (4% ethanol): series of 4–7 injections; chemical destruction of nerve; evidence of moderate benefit; useful for patients wishing to avoid surgery; may cause local inflammatory reaction; increasingly replaced by corticosteroid or surgery in many centres
• Radiofrequency ablation (RFA): percutaneous thermal ablation; evidence emerging; useful for recurrent or residual neuroma; minimally invasive
• Non-operative management should be maintained for at least 3–6 months before surgical referral

• Neurectomy (nerve excision): standard surgical procedure; the nerve is divided proximal to the TIML (transverse intermetatarsal ligament) and the neuroma excised; the nerve stump retracts proximally to a non-weight-bearing area; the nerve must be divided proximal to the transverse intermetatarsal ligament — if divided distal to the TIML, the nerve stump remains in a weight-bearing position and a painful stump (recurrent neuroma or stump neuroma) develops, the most common cause of persistent pain after neurectomy
• Surgical approaches:

• TIML release (decompression without neurectomy): division of the transverse intermetatarsal ligament to decompress the nerve without excision; preserves nerve; some evidence of efficacy; avoids permanent numbness; advocated by some surgeons as first-line surgical intervention; risk of recurrence higher than neurectomy
• Outcomes: neurectomy gives good to excellent results in approximately 80–85% of patients; permanent numbness between the affected toes is expected and should be counselled pre-operatively
• Persistent pain after neurectomy: most common cause is stump neuroma from nerve division distal to TIML; other causes include recurrence, wrong web space operated, missed diagnosis, adjacent web space neuroma; USS and MRI assess for stump neuroma; revision neurectomy with proximal division is the treatment

• Adjacent web space neuromas: simultaneous bilateral neurectomy in adjacent web spaces (e.g., 2nd and 3rd simultaneously) is controversial — risk of ischaemic necrosis of the 3rd toe when blood supply from both sides is disrupted by the dissection; most surgeons recommend staging adjacent web space neuromas by at least 6 weeks; warn patients about this risk
• Intermetatarsal bursitis coexisting with neuroma: approximately 30% of surgically confirmed neuromas have an associated bursa; the bursa is excised with the neuroma; the two conditions may be indistinguishable clinically and on USS; the management is the same
• Recurrent Morton`s neuroma after neurectomy: truly recurrent neuroma is uncommon; more commonly "recurrence" is due to a different web space neuroma, stump neuroma from inadequate proximal division, missed adjacent web space pathology, or an incorrect original diagnosis; USS and MRI of the forefoot guided by symptoms localise the pathology; revision neurectomy with proximal division at mid-metatarsal shaft level under tourniquet
• Alcohol sclerosant series: increasingly less commonly used as corticosteroid injection provides faster relief; however, where a formal sclerosant protocol is available and administered by an experienced practitioner, results are comparable to surgery in some series; useful in patients with medical comorbidities precluding surgery

• Third web space most common (65–80%); between 3rd and 4th metatarsal heads; not a true neuroma — perineural fibrosis
• Classic: burning electric pain; relieved by removing shoes; "walking on a pebble"
• Mulder`s test: mediolateral metatarsal squeeze + dorsoplantar web space pressure = palpable click + pain; sensitivity 60%, specificity 85%
• USS: imaging of choice; real-time; guides injection; sensitivity up to 95%
• Neurectomy: divide nerve PROXIMAL to TIML — distal division → stump in weight-bearing position → stump neuroma; most common cause of failed neurectomy
• Dorsal approach preferred — avoids plantar scar; TIML divided to expose nerve
• Permanent numbness between affected toes: expected after neurectomy; counsel pre-operatively
• Adjacent web space neurectomy: stage by 6 weeks minimum — risk of 3rd toe ischaemia from bilateral dissection
• Corticosteroid injection: 50–70% short-term relief; 20–30% long-term; up to 3 series before surgery
• Neurectomy success: 80–85% good/excellent; persistent pain = stump neuroma vs wrong web space vs adjacent neuroma