Abstract
Morton’s neuroma refers to a compressive neuropathy of the interdigital nerve along the distal edge of the intermetatarsal ligament in the third webspace. Clinical history and physical exam can lead to diagnosis. Footwear modification, metatarsal pads, and injections are classic nonsurgical options. Surgical excision is indicated when nonsurgical treatment fails.
Keywords
interdigital neuroma, metatarsalgia, morton’s neuroma
| Synonyms | |
| |
| ICD-10 Code | |
| G57.90 | Mononeuropathy of unspecified lower limb |
| G57.91 | Mononeuropathy of right lower limb |
| G57.92 | Mononeuropathy of left lower limb |
| G57.60 | Lesion of plantar nerve, unspecified limb |
| G57.61 | Lesion of plantar nerve, right lower limb |
| G57.62 | Lesion of plantar nerve, left lower limb |
Definition
Morton’s neuroma refers to a compressive neuropathy of the interdigital nerve along the distal edge of the intermetatarsal ligament in the third webspace. Thomas Morton theorized that the interdigital nerve was compressed by the third and fourth metatarsal heads. Further anatomic studies later dispelled that theory, as the nerve is plantar to the intermetatarsal ligament. Regardless, Morton’s neuroma is a popular term that describes the compressive neuropathy that should be more appropriately termed interdigital neuralgia.
Anatomic and radiologic studies demonstrate that rather than true neuroma, more than likely the symptoms are due to the fibrous tissue proliferation brought on by microvascular and neural microtrauma at the level of the forefoot near the intermetatarsal ligament resulting in scar, perineural fibrotic proliferation, mass effect, and dysvascularity. These factors predispose the patients to sensitivity and pain. Pain from Morton’s neuroma is most reported to be in the third webspace where the interdigital nerve receives dual supply from both the medial and lateral plantar nerves ( Fig. 91.1 ). Additionally, mobile fourth and fifth metatarsals can cause friction and tethering of the nerve against a relatively immobile third metatarsal, causing traction neuralgia. The average age of patient presenting with Morton’s neuroma is 55 years with female sex predominance (ratio 4:1). Although patients are more likely to present with unilateral symptoms, approximately 3% to 15% will have bilateral forefoot pain.
Symptoms
Primary reason for clinical visit in patients with Morton’s neuroma is activity-associated forefoot pain in the third webspace. Patients often report aching, cramping, numbness, and occasional burning sensation that may radiate to the third and fourth toes. Some patients report a retrograde Valleix phenomenon with pain radiating proximally or dorsally through the foot from the epicenter distally at the level of the transverse ligament. At times, patients describe a rolled-up sock sensation under their foot that will not subside. Symptoms tend to worsen with constrictive footwear such as high heels. The majority of patients notice pain resolution with removal of constrictive footwear.
Physical Examination
On seated exam, the pain is reproducible with palpation of the third interdigital webspace. The digital compression along with medial-lateral squeeze can simulate the pain patients experience in a constrictive shoe ( Fig. 91.2 ). Webspace tenderness is positive in 95% of patients who chose to undergo surgical excision. Mulder’s click test is helpful and has been described to be associated with a neuroma. With the patient seated and knee at 90 degrees, the physician then performs dorsoplantar compression of the third webspace while the opposite hand provides medial-lateral pressure. The click sensation is felt when this test is positive and frequently results in pain.
It is imperative to examine the forefoot for alternative causes of forefoot pain such as metatarsalgia, synovitis, radiculopathy, tarsal tunnel syndrome, plantar plate tear, and hammertoe deformities. Palpation of the metatarsophalangeal joints (MTPJs) is necessary to evaluate for synovitis or plantar fat pad atrophy. Stability of MTPJs must be examined by stabilizing the metatarsal head and performing a drawer test with the proximal phalanx. Instability of MTPJs causes potential for traction interdigital neuralgia, further traumatizing the already painful condition.
Routinely, patients should undergo Silverskiold test for equinus contracture. This test determines whether the contracture stems from the gastrocnemius versus Achilles tendon. In isolated gastrocnemius contractures, the ankle equinus contracture with the knee extended significantly improves up to 10 degrees of ankle dorsiflexion when the knee is flexed to 90 degrees. Clinically significant equinus contracture can cause additional forefoot pressure that tends to accentuate symptomatic neuroma or metatarsalgia.
Diagnostic Studies
The diagnosis of Morton’s neuroma is classically made clinically based on patient history and physical examination with sensitivity as high as 98%. Weight-bearing anteroposterior, oblique, and lateral foot radiographs can be obtained to rule out bony pathology. There is no relationship between radiographic bone length or joint angles that correlates with symptomatic Morton’s neuroma.
Advanced imaging such as ultrasound or magnetic resonance imaging can confirm Morton’s neuroma and be of value in cases where the diagnosis uncertain. They are more useful to rule out differential diagnoses such as plantar plate tears, soft tissue tumors, stress fractures, and ligamentous injuries. The size of the neuroma on these imaging modalities has no correlation with severity of clinical symptoms. There is evidence that age and size of the neuroma are predictors of further treatment within 2 years after corticosteroid injection.
Electromyography and nerve conduction velocity studies have not previously confirmed to be helpful in the diagnosis of Morton’s neuroma. However, these studies may help to exclude alternative diagnoses such as radiculopathy, peripheral neuropathy, or tarsal tunnel syndrome that may mimic a neuroma.
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