Five Centimeters Morton's Neuroma in a 46-Year-Old Woman Affected by Macrodactily

Abstract

The present article described the case of a voluminous Morton's neuroma of the third intermetatarsal space in a patient affected by macrodactily. The case was unique because of its dimensions, the uncommon surgical approach which was needed for removal, the association with macrodactily of the fourth toe with Raynaud's phenomenon, and the postoperative defect in the intrinsic muscles. The patient was operated in February 2016 by transverse plantar approach. Twelve months after surgery, the patient complained for hypoesthesia on third and fourth toes with inability to actively spread the toes and enlargement in the second interdigital space. The dimensions of the lesions may be explained with the presence of macrodactily in the fourth toe with occasional Raynaud's phenomenon, which may have caused an abnormal arrangement of the nerve branches for the fourth interspace with related microtrauma. A plantar approach was highly recommended as the size of the lesion forced it to the plantar surface of the foot. The inability to actively spread the toes and the enlargement of the second interdigital space are likely to be related to a deficiency of the interosseous muscles, innervated by the deep branch of the lateral plantar nerve, which had probably been sacrificed because of the size of the lesion and the subversion of the surrounding anatomical relationships.

Keywords

Morton - foot - neuroma - macrodactily - Raynaud

Introduction

Morton's neuroma is a very common cause of metatarsalgia, and consists in an interdigital nerve disease of the foot, classically located at the third intermetatarsal space.[1]

It was suggested that the common digital nerve to the third interspace is thicker than the others, as it results from an anastomosis between branches from the two nerve trunks.[2] [3] [4] Another anatomical factor is the increased mobility of the fourth radius (moving on the cuboid), compared with the third (fixed to the cuneiform). Some believe that taut distal metatarsal transverse ligament plays a critical role in compressing the interdigital nerve.[5]

A longitudinal dorsal approach centered on the interspace is the preferred choice by most surgeons. The advantages of a dorsal approach[5] [6] as compared with plantar approach are described as the ability to release the intermetatarsal ligament; the incision being in the nonweight bearing surface of the foot, allowing for early rehabilitation; good overview as to follow the nerve proximally; and the plantar cutaneous nerves are easier to find and excise.

The advocates of plantar approach believe that this approach is safe, and that there is no need to release the deep transverse ligament.[6] [7] A longitudinal plantar approach must be performed exactly below the intermetatarsal space and thorough with resolution through the fat pad to prevent the dissection.[8] [9] It is possible to perform a transverse plantar approach just proximal to the flexion skin fold.[10] [11] This prevents approach to the load portion, but it must be extended to the adjacent spaces, with significant dissection, possible atrophy of the fat pad, and difficulty following the nerve proximally.[5]

Postoperative wound infection, hematoma, and scar problems were significantly higher in patients having plantar approach.[8]

A hypoesthesia or numbness in the supplying area of the resected nerve was detected in 72% of the feet. The pattern of numbness was quite variable and it was bothersome in a limited percentage of cases (17%).[6] Sometimes the residual discomfort is described as the feeling of walking on cotton, or to have jammed sock under the foot.

The present case regards a 46 years old woman affected by a voluminous neuroma in the third webspace, pushed toward the plantar surface of the foot. It was a unique case because of various aspects: its dimensions, the uncommon surgical approach which was needed for removal, the association with macrodactily of the fourth toe with Raynaud's phenomenon, and the postoperative defect in the intrinsic muscles. After a detailed case presentation, all these aspects will be discussed.

Case Presentation

A 46-year-old woman came to our attention complaining of a painful swelling in the plantar aspect of the foot, just beneath the metatarsal heads. The pain was present for 3 years. At the time of the appearance of pain, the swelling had already grown to final dimensions.

The patient complained of morning pain, and feeling of hardening under the foot, which then was relieved during the day. Then sudden sharp pain preceded by numbness at the toes. When wearing closed shoes, she had to take them off and massage her foot to reverse the pain.

At physical examination, a macrodactily of the fourth toe was noted, and the X-rays revealed no bone deformities. The patient reported occasional Raynaud's phenomenon. The patient reported no significant medical history and no allergies, and she did not take drugs.

She was operated in February 2016 for mass excision and histological examination. The patient was positioned supine on the operating table, with a tourniquet at the proximal thigh. Surgical approach was performed through a plantar transverse incision just proximal to the flexion skin fold, from the fourth to the second intermetatarsal space ([Fig. 1]). The mass was directly retrievable under the skin, and the dissection revealed its nervous nature. The lesion was in continuation of the common digital nerve for the third space, and distally it bifurcated in the two digital nerves.

Fig. 1 Dissection of the lesion through a plantar transverse approach.

The lesion was excised trying to follow the common digital nerve proximally and to isolate the two digital nerves distally. At final examination, the lesion was yellowish and tender and it was measured out to be 5 × 3 cm ([Fig. 2]).

Fig. 2 The lesion was removed including bifurcation into the two digital nerves, and measured.

Histological examination revealed a fibrous tissue with poor cellular component and various nerve trunks at the periphery, interspersed with fibrosis. The score sheet indicated a Morton's neuroma.

After the operation, the patient had a compressive bandage, and she was discharged the day after operation, walking with postoperative shoe for 15 days, only for short periods. The bandage was maintained for 7 days, and then a simple medication was performed. Suture was removed after 15 days: the wound was closed with subcutaneous hematoma. Gradually she was allowed to wear a normal shoe.

Six and 12 months after the surgery, the patient was revised: the surgical wound was perfectly healed ([Fig. 3]), with no fat pad atrophy, subcutaneous adhesions, or calluses. The patient could walk with every kind of footwear and without any plantar discomfort. But she complained for hypoesthesia on the third and fourth toes, with inability to actively spread the toes and enlargement in the second interdigital space ([Fig. 4]).

Fig. 3 The surgical wound 6 months after operation was perfectly healed, and no calluses were evident.

Fig. 4 The bearing foot showed an enlargement in the second interdigital space.

Discussion

Morton's neuroma is a very common forefoot disease. Its dimensions are variable, but usually they are of 5 to 10 mm.[12] [13] Even small lesions, however, may be symptomatic, and in this case are even more difficult to diagnose.[14]

A neuroma of this size (5 cm) had never been reported in the literature, and probably represents an exception, as its etiology differs from classic Morton's neuroma. The presence of a deformity of the fourth toe (macrodactily), without bone involvement, with occasional Raynaud's phenomenon, may have caused an abnormal arrangement of the nerve branches for the fourth interspace with related microtrauma.

In this case, a plantar approach was highly recommended as the size of the lesion forced it to the plantar surface of the foot, becoming palpable beneath the skin. The transverse incision allowed us to have enough exposure for accurate dissection of the neuroma and its removal.

Twelve months after surgery, the patient had no wound problems related to plantar approach. The inability to actively spread the toes and the enlargement of the second interdigital space are likely to be related to a deficiency of the interosseous muscles, which are innervated by the deep branch of the lateral plantar nerve, which had probably been sacrificed because of the size of the lesion and the subversion of the surrounding anatomical relationships.

An abnormal arrangement of the nerve branches should be considered when a Morton's neuroma is associated with forefoot deformities.

Conflict of Interest

None declared.

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Publication History

Received: 15 September 2017

Accepted: 13 April 2020

Article published online:
20 May 2020