Morton's Neuroma

Populations and Risk Factors

• Women significantly more than men (4:1 to 10:1), driven by footwear patterns
• Peak incidence between 40 and 60 years
• Narrow or pointed-toe footwear and high heels — shifting body weight onto the metatarsal heads
• Morton's foot (second metatarsal longer than first) — alters forefoot weight distribution
• Repetitive forefoot loading: running, dancing, prolonged standing on hard surfaces
• Pre-existing forefoot deformities: hallux valgus, hammertoe, pes planus (excessive pronation widens the forefoot under load, increasing intermetatarsal shearing)
• First ray hypermobility — transfers load laterally to the lesser metatarsals

Causes and Pathophysiology

• Why the third interspace: The common digital nerve here is formed by the convergence of branches from both the medial and lateral plantar nerves. This makes the nerve bundle thicker than at other interspaces. At the same time, the third interspace is the narrowest of the four. A thicker nerve in a tighter space creates unique vulnerability. The second interspace is the next most commonly affected.
• Transverse metatarsal ligament compression: The deep transverse intermetatarsal ligament is a band connecting the metatarsal heads that forms a rigid roof over the nerve. During weight-bearing, the metatarsal heads compress together — the nerve is trapped between the bones below and the ligament above. This creates a fixed compression point the nerve cannot escape during push-off.
• Repetitive microtrauma and the fibrotic cycle: Each toe-off phase compresses the nerve against the transverse ligament. Over thousands of cycles, this triggers chronic inflammation in the perineural sheath. The inflammation progresses to perineural fibrosis — the tissue surrounding the nerve thickens, scars, and loses elasticity. The fibrotic mass enlarges, which increases compression, which accelerates fibrosis — a self-reinforcing cycle. The mass can become large enough to palpate as a nodule, producing the characteristic "walking on a marble" sensation.
• Histology (not a true neuroma): The lesion consists of thickened epineurium and perineurium with dense collagen deposition, vascular changes, and secondary axonal degeneration. There is no neoplastic nerve growth.
• Footwear as a modifiable mechanism: A 3-inch heel shifts approximately 76% of body weight to the metatarsal heads. Narrow toe boxes compress the metatarsal heads together, further reducing interspace width. This explains why symptoms resolve immediately upon removing constrictive footwear and why footwear modification is the single most effective non-surgical intervention.
• Mulder's click mechanism: When the metatarsal heads are squeezed laterally, the fibrotic mass is forced to sublux (pop) between the metatarsal heads, producing a palpable and sometimes audible click. This is pathognomonic for the condition.

Signs and Symptoms

• Forefoot pain: Sharp, burning, or electric-shock pain localized to the third (or second) intermetatarsal space, radiating distally to the adjacent toes
• "Walking on a marble": Sensation of stepping on a pebble or bunched sock — corresponds to the fibrotic nodule described in Pathophysiology
• Burning and paresthesia: Burning across the forefoot and numbness or tingling in the affected toes, reflecting progressive nerve compression
• Footwear-related pattern: Worse in narrow or high-heeled shoes; improves or resolves when barefoot or in wide-soled shoes — nearly pathognomonic on history alone
• Activity aggravation: Increases with walking, running, push-off activities, and prolonged standing on hard surfaces; may build progressively through the day
• Mulder's click: When present on clinical examination (see Pathophysiology for mechanism)

Assessment Profile

Subjective Presentation

• Chief complaint: "Sharp pain in the ball of my foot" or "burning between my toes" — often with "it feels like there's a marble in my shoe"
• Pain quality: Patients describe it as burning, electric, or sharp; they localize it to the forefoot and report it shooting into the toes; numbness or tingling in the web space is common
• Onset: Ask about timeline and triggers — onset is insidious over weeks to months; correlate with footwear changes (new shoes, increased heel height) or increased weight-bearing activity; no single traumatic event
• Aggravating factors: Ask specifically about shoe type — patients will confirm narrow or heeled shoes are worst; also: walking, running (especially push-off), prolonged standing, squeezing the forefoot (tight socks, compression from adjacent toes)
• Easing factors: Removing shoes provides rapid relief — patients often stop mid-walk to take shoes off; going barefoot or wearing wide, flat shoes; massaging the forefoot
• Red flags: Persistent pain at rest unrelated to footwear or weight-bearing, progressive swelling, or unexplained warmth — suspect stress fracture, MTP joint synovitis, or other forefoot pathology; refer for imaging if presentation is atypical

Observation

• Local inspection: No visible swelling or deformity in early stages; chronic cases may show subtle widening of the affected toe gap; callus under the metatarsal heads indicates altered weight-bearing; assess footwear — narrow toe box, heel height, and worn sole pattern are diagnostically informative
• Posture: May show lateral weight shift to the unaffected foot during standing; excessive pronation may be visible as a contributing factor
• Gait: Antalgic modification during push-off — shortened stride and reduced toe-off on the affected side; patient may roll the foot laterally to avoid loading the medial forefoot

Palpation

• Tone: Intrinsic foot muscles (lumbricals, interossei) may be hypertonic on the affected side; plantar fascia may be taut at the medial band; calf complex (gastrocnemius, soleus) often chronically hypertonic — contributing to the forefoot overloading described in Pathophysiology
• Tenderness: Focal tenderness in the affected intermetatarsal space, palpated by pressing dorsally into the web space from the plantar surface; a palpable nodule (the fibrotic mass) may be detected on careful interspace palpation; Mulder's click is elicited here — one hand compresses the metatarsal heads laterally while the other applies dorsal-plantar pressure at the interspace
• Temperature: Usually normal; mild warmth may be present during acute flare-ups but is not a primary finding — significant warmth or heat suggests an inflammatory or infectious process and warrants investigation
• Tissue quality: Fibrotic thickening palpable in the interspace in established cases; reduced plantar fascial mobility; forefoot tissues may feel inelastic on dorsal-plantar glide; intermetatarsal joint play may be restricted

Motion Assessment

• AROM: Active toe dorsiflexion at the affected MTP joints may provoke interspace pain — dorsiflexion tightens the plantar plate and increases tension on the nerve as it passes under the transverse metatarsal ligament; active push-off during walking reproduces symptoms
• PROM / end-feel: Passive toe dorsiflexion may reproduce symptoms; end-feel at the MTP joints is typically normal (tissue stretch) — the provocation is positional nerve compression, not joint restriction; passive metatarsal spreading may relieve symptoms (a positive diagnostic indicator and treatment guide)
• Resisted testing: Generally normal; no myotomal weakness expected; pain on resisted toe flexion is uncommon but possible if the fibrotic mass is large enough to interfere mechanically with the flexor tendons

Special Test Cluster

Diagnostic note: Mulder's click is pathognomonic — when clearly present, it confirms the diagnosis clinically. Morton's squeeze test adds sensitivity but is positive in metatarsalgia, stress fracture, and MTP synovitis. If significant numbness or paresthesia extends beyond the local distribution, add tibial nerve neurodynamic testing to rule out proximal entrapment at the tarsal tunnel.

Differential Assessment