Morton's interdigital neuroma: instructional review

Abstract

The terminology 'Morton's neuroma' may represent a simplification of the clinical condition as the problem may not be a benign tumour of the nerve, but neuropathic foot pain associated with the interdigital nerve.Foot and ankle pathomechanics leading to metatarsalgia, clinical examination and differential diagnosis of the condition and imaging of the condition, for differential diagnosis, are discussed.Nonoperative management is recommended initially. Physiotherapy, injections (local anaesthetic, steroid, alcohol), cryotherapy, radiofrequency ablation and shockwave therapy are discussed.Operative treatment is indicated after nonoperative management has failed. Neuroma excision has been reported to have good to excellent results in 80% of patients, but gastrocnemius release and osteotomies should be considered so as to address concomitant problems.Key factors in the success of surgery are correct diagnosis with recognition of all elements of the problem and optimal surgical technique. Cite this article: EFORT Open Rev 2019;4:14-24. DOI: 10.1302/2058-5241.4.180025.

Keywords: Morton’s neuroma; interdigital nerve; metatarsalgia.

Fig. 1

Pictures a–d are of different patients presenting with plantar forefoot pain associated with Morton’s neuroma. Plantar skin callosities are evidence of forefoot overload (a). Planovalgus feet (b) and feet with hallux valgus deformities (c) result in first ray elevation and overload of the second and third rays, whereas cavus feet (d) are often associated with plantar prominence of the metatarsal heads.

Fig. 2

The dotted lines represent the ‘normal forefoot cascade’. The longer second, third, and fourth metatarsals result in overload.

Fig. 3

When the knee is extended the ankle cannot be passively dorsiflexed to 90 degrees. This is a sign of tight calf muscles. Knee flexion results in release of the tension of gastrocnemius, allowing ankle dorsiflexion beyond neutral. If the ankle cannot be dorsiflexed despite knee flexion, then the tightness affects the gastrocsoleus complex and/or the Achilles tendon and not just the gastrocnemius (Silfverskiold test).

Fig. 4

Web-space tenderness, aggravated by squeezing the foot (a) is usually positive in patients with Morton’s neuroma. Dorsal pain at the level of the metatarsophalangeal joint (white circle, b) when passively plantarflexing the toe is a sign of metatarsophalangeal joint synovitis.

Fig. 5

When metatarsophalangeal-joint related pain is suspected, an image-guided injection (demonstrating an arthrogram) can aid differential diagnosis.

Fig. 6

The examiner pushes with the side of his/her thumb deep into the intermetatarsal space.

Fig. 7

Positive Tinel sign on percussion of the plantar intermetatarsal space can be a sign of Morton’s neuroma.

Fig. 8

The hypoechoic area within the green margins represents a Morton’s neuroma.

Fig. 9

Morton’s neuroma of the third interdigital space (white arrow) shown on MRI.

Fig. 10

A 68-year-old male patient is dissatisfied after ‘failed’ surgery to excise a third-web-space Morton’s neuroma at another hospital. He still has forefoot pain. On examination he has diffuse, poorly localized pain across the forefoot, a stiff and painful hallux metatarsophalangeal joint and significant gastrocnemius tightness. He has had an ultrasound showing a ‘probable nerve stump neuroma’, whereas a guided injection offered no pain relief. He has never had foot radiographs before. Radiographs show the advanced degenerative changes in the hallux metatarsophalangeal joint, and clawing of the second toe.

Fig. 11

The MRI scan of the patient’s foot discussed in Figure 10 revealed intermetatarsal bursitis (white arrow, left), synovitis (white arrow, right) and no nerve stump neuroma.

Fig. 12

The medial gastrocnemius muscle aponeurosis is released at its proximal end.

Fig. 13

A 42-year-old female patient presented with recurrent hallux valgus, second-toe progressive deformity and neuritic symptoms arising from the second web space. A forefoot reconstruction was needed, in addition to the neurectomy.

Fig. 14

The intermetatarsal ligament is cut through a dorsal approach.

Fig. 15

It is essential to dissect the two digital branches distally, to ensure that the interdigital neuroma has been correctly identified.

Fig. 16

The nerve trunk is dissected proximally from the plantar aspect. It is important to dissect a long segment, deep into the foot.

Fig. 17

A long segment of nerve (3–4cm) is dissected out, in order to ensure that the nerve stump retracts proximal to the weight-bearing area of the metatarsal heads.