Concurrent Heuter’s and Morton’s Neuromata Following Hallux Valgus Surgery: A Rare Case and Review of Terminology

Abstract

Visual Abstract.

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Introduction

Morton neuroma, also known as interdigital neuroma, is a frequent cause of forefoot pain. It was first described by Civinini in 1835, with Durlacher further characterizing its clinical presentation in 1845. However, Thomas Morton’s 1876 description of pain in the fourth metatarsophalangeal joint led to the eponymous designation. ⁷ Morton neuroma is most commonly found in the third intermetatarsal space, with approximately 66% of cases affecting this location. This pathology predominantly affects women, with a 4:1 female-to-male ratio, and typically manifests in the fifth decade of life. ⁴

The etiology of interdigital neuromata remains debated, with multiple theories proposed, including chronic trauma, ischemia, intermetatarsal bursitis, and nerve entrapment (Table 1). Chronic trauma results from repetitive dorsiflexion and hyperpronation, whereas ischemia contributes via degenerative arterial changes. Intermetatarsal bursitis can lead to fibrosis and subsequent nerve compression, whereas the deep transverse metatarsal ligament is implicated in nerve entrapment.^2,3

Table 1.

Theories Proposed in Literature on the Etiology of Interdigital Neuromata. ^a

Etiologic Theory	Key Points
Chronic trauma	• Repetitive trauma to the nerve due to dorsiflexion and foot hyperpronation • Contraction of intrinsic toe muscles3,4
Ischemia	• Degenerative changes in digital arteries  ○ Ischemia in the vasa nervorum leading to nerve degeneration 5
Intermetatarsal bursitis	• Inflammation of the adjacent bursa  ○ Fibrosis and nerve compression 3
Nerve entrapment	• Compression by the deep transverse metatarsal ligament (DTML) during ambulation, particularly at the nerve bifurcation 4

^aThe latest trends rely on a combination of several that acts as synergy.

Although Morton neuroma is well documented, Heuter neuroma—affecting the first intermetatarsal space—is exceedingly rare, with minimal reports of its occurrence following hallux valgus surgery. This case presents a unique instance of concurrent Heuter and Morton neuromata in the same foot postoperatively, highlighting both its rarity and the diagnostic and therapeutic complexities associated with the terminology of these neuropathies.

Case Report

A 38-year-old female military personnel presented with dysesthesia and numbness in the plantar aspect of her left foot, primarily affecting the first and third intermetatarsal spaces. Ten years earlier, she had undergone percutaneous hallux valgus correction with favorable early outcomes. However, she progressively developed pain exacerbated by walking, accompanied by toe paresthesia. Physical examination revealed a positive Mulder test and plantar interdigital percussion, suggesting interdigital neuropathy.

Imaging Studies

Initial weightbearing radiographs were unremarkable (Figure 1). MRI revealed 2 pseudonodular lesions suggestive of neuromata: one in the first intermetatarsal space (18 mm) and another in the third space (11 mm) (Figure 2A and B).

Figure 1.

Anteroposterior weightbearing radiograph showing the consequences of hallux valgus surgery and signs of recurrence. Decrease in the first, second, and third intermetatarsal space.

Figure 2.

Magnetic resonance images that correspond to (A) coronal and (B) axial T1 sequences, respectively. In both images, it is possible to see the injury between the first and third digital spaces and that extends to the head of the first-second and the third-fourth metatarsals.

Surgical Technique

The procedure was performed under locoregional anesthesia. Two dorsal incisions were made over the first and third intermetatarsal spaces to access the neurovascular structures directly (Figure 3). A plantar approach was avoided to prevent painful scarring. The interdigital nerves were meticulously dissected and isolated. Both neuromata were excised en bloc to minimize recurrence risk, and specimens were sent for histopathologic analysis.

Figure 3.

(A and B) Intraoperative images showing the dorsal approach to the first and third space. This approach provides direct access to the lesion and allows for thorough dissection of the neuroma, avoiding damage to neighboring structures and its en bloc removal. Painful plantar scars that affect the biomechanics of the foot are avoided.

Histology

Histopathologic examination confirmed the presence of nerve fiber proliferation with perineural fibrosis, consistent with interdigital neuromata. The presence of Pacinian and Meissner corpuscles supported chronic compression-induced nerve damage.

Results

Postoperative recovery was favorable, with complete resolution of symptoms from the first day. At 1 year, the patient remained asymptomatic, with no recurrence or complications. The AOFAS score improved from 30 to 95 points, and the VAS for pain decreased from 9 to 1. The patient resumed unrestricted daily activities.

Discussion

The terminology and classification of interdigital neuromata remain controversial. Morton initially described pain at the fourth metatarsophalangeal joint, leading to inconsistencies in modern classifications. ⁷ Over time, neuromata in other intermetatarsal spaces were described, including Heuter in the first space, Hauser in the second, and Iselin in the fourth (Figure 4). This lack of precision complicates classification and hinders the comparability of studies, leading to inconsistencies in the literature. Multiple authors have advocated for terminology that specifies the affected nerve and anatomical location, for example, “compression of the common plantar digital nerve in the first intermetatarsal space,” which could replace ambiguous eponyms. ¹

Figure 4.

Visual representation of the interdigital plantar nerves and their main entrapment places. The eponyms of the neuromas are specified, highlighting the first and third spaces that correspond to the case presented. Adapted from Gray: Anatomy of the Human Body (1918).

In this context, various etiologic theories suggest that interdigital neuromata result from chronic mechanical overload and nerve entrapment. Although a direct causal link between hallux valgus surgery and the development of Heuter neuroma has not been established, long-term alterations in forefoot biomechanics may act as contributing factors. Postoperative changes in load distribution and alignment—such as first-ray insufficiency following aggressive lateral release, increased dorsal metatarsal mobility, or restrictive fibrosis—could potentially elevate compressive forces on the interdigital nerve. Altered deep transverse metatarsal ligament–neurovascular spatial dynamics or progressive foot pronation destabilizing the medial arch may also contribute to forefoot overload. These mechanisms, alongside intraoperative neural irritation or entrapment within scar tissue, may collectively predispose to neuroma formation, even in cases managed with percutaneous techniques lacking osteotomies.^3,8

The dorsal surgical approach was selected to minimize plantar scarring and optimize nerve visualization. A recent systematic review by Lee et al ⁶ supports this approach, demonstrating lower rates of postoperative scar tenderness, although with a slightly higher incidence of sensory reduction compared with the plantar approach.

The concurrent appearance of neuromata in both the first and third intermetatarsal spaces following hallux valgus surgery is, to our knowledge, unprecedented. Although causality cannot be assumed, the presence of multiple neuromata should be considered among the differential diagnoses in patients with persistent forefoot symptoms after correction procedures (Table 2).

Table 2.

Differential Diagnosis Between the Most Common Places of Plantar Nerve Entrapment at Its Interdigital Exit and Possible Characteristics Associated With the Patient With the Diagnostic Condition.

Interdigital Space	Differential Diagnosis	Associated Characteristics
First interdigital space	1. First space neuroma 2. Compression of the medial plantar nerve 3. Hallux valgus/varus 4. Flexor hallucis longus (FHL) tendinopathy 5. Stress fractures	Irritation medially, abnormal alignment, acute or chronic fractures
Second interdigital space	1. Second space neuroma 2. Transfer metatarsalgia 3. Intermetatarsal bursitis 4. Compression due to flat or cavus foot 5. Intrinsic muscle tendinopathy	Metatarsal overload, bursitis, chronic inflammation, nerve compression symptoms
Third interdigital space	1. Third space neuroma 2. Entrapment of the lateral plantar nerve 3. Freiberg disease 4. Intermetatarsal bursitis 5. Long metatarsals	Overload, structural deformity, fracture-like symptoms
Fourth interdigital space	1. Compression of the lateral plantar nerve 2. Intermetatarsal ligament injury 3. Peroneal longus tendinopathy 4. Metatarsalgia 5. Intermetatarsal synovitis	Increased flexibility, lateral irritation, mechanical pain in the lateral column

Kim et al previously reported a case of Heuter neuroma after Akin osteotomy and soft tissue release. In both scenarios, postsurgical fibrosis likely contributed to symptom onset. ⁵

In our patient, progressive foot pronation likely intensified the stress on the interdigital nerves; this observation aligns with the notion that postoperative alterations in forefoot loading, including factors such as deep transverse metatarsal ligament spatial shifts and fibrotic tethering, may predispose to neuroma formation.

Conclusion

We present a rare case of concurrent Heuter and Morton neuromata following hallux valgus correction, underscoring the diagnostic challenge of persistent forefoot pain after surgery. Although a direct causal relationship cannot be definitively established, postoperative biomechanical changes and fibrosis may contribute to neuroma development. Importantly, this case highlights the need to include first intermetatarsal space neuroma in the differential diagnosis for post–hallux valgus pain, particularly when symptoms are atypical or refractory. A dorsal surgical approach provided excellent visualization and symptom resolution, and may be preferred in revision settings to minimize plantar scarring and facilitate early recovery. Further study is warranted to better characterize the clinical relevance and optimal management of Heuter neuroma.