Access Keys:
Skip to content (Access Key - 0)

Morton's Neuroma

Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

Morton's neuroma (also known as an intermetatarsal neuroma or interdigital neuroma)  is is a  common common cause of forefoot pain and disability. It presents as a sharp, burning  sensation sensation in the web-space between the toes; most typically, it is found between the 3rd and 4th toes. Note that the pathology of this condition is not a neuroma, per se (ie, it that is, Morton's neuroma is not a "benign growth of nerve tissue"   , as the definition of the word "neuroma" ) , but is rather a perineural fibrosis, or would imply);  rather what is seen is an overgrowth of the tissue tissue around the nerve: perineural fibrosis.  The   The etiology of the condition is believed to be related to localized repetitive overload of the forefoot and it is considered a type of "metatarsalgia."  It is associated with claw toes, a tight calf muscle, and wearing shoes that have a tapered toe box or high-heels.    

 

Structure and function  

Morton's neuroma usually affects the third interdigital nerve in the third webspace between the third and fourth toes (80-85% of cases) or the second common digital nerve in the second webspace (10-15% of cases). 

 

There may be an anatomic and biomechanical reason for the frequency of the involvement of the third common digital nerve in Morton's neuroma. Firstly, the common digital nerve of the third webspace is the largest digital nerve and is usually a confluence of the terminal branches of the medial and lateral plantar nerves (the two terminal divisions of the tibial nerve) (Figure 1).

Image Removed

Figure 1. Plantar anatomy

Secondly, the space that the nerve occupies is subject to shearing forces as the relatively mobile 4th metatarsal can stress the nerve against the relatively fixed 3rd metatarsal. Thirdly, the nerve may experience compression during the heel-rise phase of gait. When the weight-bearing portion of the foot is reduced to the forefoot hyperextension of the metatarsophalangeal joints occurs.  This compresses the common digital nerve and metatarsal heads against the tough and unyielding intermetarsal ligament.

The neuroma itself The medial and lateral plantar nerves arise from the posterior branch of the tibial nerve and innervate the sole of the foot. The medial plantar nerve is the larger of the two and supplies the great toe, the second and third toes, and the medial side of the fourth. This corresponds to the distribution of the median nerve in the hand.  The lateral plantar nerve supplies the fifth toe and lateral half of the fourth toe, just as the ulnar nerve does with the fingers. These nerves split into common digital nerves as they course distally. Just proximal to the web space (that is, near the metatarsal head), the nerves bifurcate into interdigital nerves, one branch medially and one laterally, coursing out to the distal aspect of the two toes.  Unlike the hand, where anastomoses between the median and ulnar nerves are rare, in the foot, the third interdigital nerve is composed of confluent fibers from both the medial and lateral plantar nerves.  In about 85% of all cases, Morton's neuroma affects this third nerve, likely owing to its size (among other considerations). Thus, there are symptoms in the third and fourth toes. In the remaining 15% of cases, it is the second common digital nerve in the second webspace that is affected.

 

FIGURE:  need a good line drawing of nerve anatomy relative to ligament. here is a not so good rough draft (jb)

Image Added

The neuroma is usually densely adherent to the intermetarsal ligament. It is part of the neurovascular bundle, which is fusiform in shape.2 The tissue itself   The tissue is usually a soft-pale yellow or whitish glistening soft mass (Figure 2). Histologically, there is evidence of fibroblast and Schwann cell proliferation , represented by extensive juxta- and intraneural fibrosis as well as within extensive perivascular and subintimal fibrosis. 3 There is demyelination and axonal damage. Additionally, Renaut bodies (subperineural hyalinized nodules) are present.

Image Removed

Figure 2. Intra-operative image of Morton's neuroma as a fusiform swelling of the nerve

The exact etiology and pathogenesis Additionally, demyelination,  axonal damage and hyalinized nodules (so called Renaut bodies) under the perineurium are present.

The exact etiology of Morton's neuroma is still a point of contention. There are many theories. Morton suggested that enlargement or a neuroma of the digital branches of the lateral plantar nerve not known. The eponymous Morton himself suggested that capsulitis of the metatarsophalangeal joint was the source of pain. 4 Neuritis has also been suggested.5 Betts Betts speculated that the contraction of the flexor digitorum brevis caused the nerve to shear against the intermetarsal ligament, which in turn causes inflammation. Another theory popularized by Nissen states that the intermetatarsophalangeal bursa balloons out, causing traction on the digital nerve adjacent to the digital nerve. This leads to is that bursal enlargement produces an ischemic effect on the nerve.6 Current theories postulate that Morton's neuroma is a consequence of the combination of repetitive mechanical and ischemic trauma, entrapment, and tethering.3

Patient presentation

Most chronic pain in the forefoot is not the result of a Morton’s neuroma, but rather is from metatarsalgia. Metatarsalgia occurs from repetitive compression loading of the structures of the forefoot and the resulting chronic tissue injury and inflammation (ex. lesser MTP joint synovitis).Therefore a careful history and physical examination must be made to exclude other pathologies in the differential diagnosis. .  Last, normal biomechanics alone may be responsible: shearing forces are produced when the relatively mobile 4th metatarsal moves against the relatively fixed 3rd metatarsal, and the nerve may be compressed against the intermetarsal ligament during the heel-rise phase of gait. 

 

 

Patient presentation

 

A patient with a Morton's neuroma often complains of a burning, sharp pain located in between the third and fourth toes. This pain is often plantar at the metatarsal heads and radiates distally on either side of the toe; it can also radiate from the forefoot up the leg proximally. The pain is often exacerbated with wearing tight or constricted shoes and alleviated while walking barefoot. A patient may describe characteristically two qualitatively and temporally different paindistinct pains. The first , is an intense pain that lasts for about 5- 10 minutes and is precipitated by direct compression of the neuroma. This pain then becomes a gives way to a second type, a dull ache for the next 2-3 hours.2,3 One feature of a Morton's neuroma is that a patient may need to rest after walking, remove the shoe, and massage the area of discomfort for moderate relief.7 This may occur several times throughout the day. that is present for a few hours and abates with rest, removal of one’s shoe and direct massage. Patients may also complain of the sensation of a stone or pebble under the toes or forefoot when walking.

On visualization, the The patient's foot is often appears to be unremarkable, without signs of intermetatarsal bursitis or dorsal bulging. On palpation, the usual location of pain is at the interspace between the metatarsal heads. Therefore, one must examine the metatarsophalangeal joints for synovitis or instability (metatarsophalangeal drawer test). Interdigital skin sensation is often decreased.

A useful test for Morton's neuroma is the "lateral squeeze test". This test is performed with the index and thumb on the dorsal and plantar aspect of the painful intermetatarsal space. The forefoot is then compressed with the opposite hand by squeezing together the metatarsal heads. The test is positive if : when the forefoot is compressed by the examiner’s hands a painful or palpable click is felt. This  "Mulder's click" is likely due to might be produced by the subluxation of the neuroma between the metatarsal heads.8

Objective Evidence

Morton's neuroma is usually a clinical diagnosis made on a thorough history and physical examination. Imaging, however, may be necessary to rule out the differential diagnosis. Occasionally, an X-ray may show a faint radiopaque mass and lateral toe deviation. 3 MRI (Figure 3) and ultrasonography (Figure 4) MRI and ultrasound may also confirm a Morton's neuroma. An MRI will show inflammation surrounding the neuroma, as seen in T2-weighted images. An ultrasound will show a non-compressible hypoechoic interdigital mass with or without a bursal effusion.

Image Removed

Figure 3. MRI of inflammation surrounding Morton's neuroma

Image Removed

Figure 4. Longitudinal and transverse ultrasound views of Morton's neuroma

While early studies of imaging showed that the clinical utility of these modalities is questionable,9 most studies did not evaluate a Mortons' neuroma with today's more sensitive MRI magnets and ultrasonography equipment. Owens and colleagues showed that an MRI may have a sensitivity of 97% in patients with symptomatic neuromas, but showed neuromas in 25% of patients without symptoms.10 Sharp et al evaluated 29 confirmed cases of Morton's neuroma that were evaluated with an MRI, ultrasound, and physical examination. MRI and ultrasound's accuracy was dependent on the size of the lesions. Physical exam proved to be the most sensitive and specific modality.11

Epidemiology

Morton's neuroma is a subset of metatarsalgia and as such the epidemiology of the disease is not clearly defined.  The incidence and prevalence of pure Morton's neuroma (as opposed to metatarsalgia with a  component of Morton's neuroma) is not known.12 Typically, women ages 45-50 are affected, and although men are also affected, women account for the overwhelming majority of cases.12,13 Both feet are equally affected, although bilateral complaints are rare. It is also relatively uncommon to find two neuromas in the same foot.

Differential diagnosis

Included in the differential diagnosis for Morton’s neuroma are metatarsalgia, metatarsophalangeal synovitis/instability, stress fracture of the phalanges or metatarsals, Freiberg's infraction, tarsal tunnel syndrome, peripheral neuropathy,  An injection of a local anesthetics may confirm the diagnosis of a Morton's neuroma by producing an immediate (though temporary) amelioration of the symptoms.

 

Epidemiology

The incidence of Morton's neuroma is not known. What is known is the incidence is about 5 times higher in women than in men, but the left and right feet are equally affected.  The typical patient is about 45 years old.

Differential diagnosis

Most chronic pain in the forefoot is not the result of a Morton’s neuroma. Other more common sources of metatarsalgia (the medical term for forefoot pain) are peripheral neuropathy (from diabetes most likely); stress fractures of the metatarsals; synovitis or other inflammation; and trauma. Also to be considered are Freiberg's infraction (avascular necrosis of the metatarsal head), tarsal tunnel syndrome, infection, and tumors. A thorough physical examination is essential in differentiating among these possible diagnoses.

Metatarsalgia will present with more plantar pain at the metatarsal head (usually 2nd or 3rd). A stress fracture may be ascertained with a history of trauma/overuse and pain with activity; the pain can be reproduced over the fracture site. Freiberg's infraction usually occurs in adolescent females with dorsal pain over the 2nd metatarsal head. Clinical suspicion for infection and tumors must always remain high. Areas of ulceration and erythema may point to infection.

Red flags

...

Red flags

Foot pain in patients with diabetes can be the harbinger of complications. A history of diabetes, thus, should motivate an especially detailed examination.

Treatment options and Outcomes

Non-operative Treatment

When a diagnosis of Morton's neuroma is made, some surgeons believe that conservative management is never warranted because the pain will persist and worsen as the neuroma enlarges.2 However, several conservative treatment modalities are available. There is no agreed-upon treatment algorithm, but most believe that these treatments should be tried from 3 months to 1 year.1,3

Comfort Shoes

Firstly, a patient should wear wide, comfortable treatment is the best initial approach.  The patient should be instructed to wear shoes with a large toes box .1 Their shoes should be low-heeled and may be supplemented with either and low heels; a metatarsal pad or a custom orthotic . The pads help can be used to relieve metatarsal head pressure . The custom orthotics seek to limit foot subtalar pronation, which should theoretically limit the mobility of the first ray and reduce forefoot abduction.14 Unfortunately, a randomized trial failed to show any subjective pain differences between the pronated orthotic group and the control group.14

Anti-Inflammatory Medications

Secondly, a person may try to decrease the neuroma pain and inflammation with non-steroidal as well.  The use of anti-inflammatory medications .

Physical Therapy

Physical therapy has also been used.15 Ultrasound, whirlpool, massage, and electrical stimulation are often used, although their efficacy has not been studied.

Corticosteroid Injections

Another treatment modality is an intermetatarsal corticosteroid and local anesthetic injection. It is imperative that the needle traverses the intermetatarsal ligament to enter the bursa and infiltrate the neurovascular bundle. While some studies show that 47% of people may experience relief with injections,16 others fail to show any long-term relief.17 Recently, studies have looked at injection of either phenol or alcohol. An electrode-guided injection of phenol proved to be effective in 80.3% of cases.18 Ultrasound-guided injection of alcohol gave 84% of patients total relief, with partial relief to 94%.19 However, there is evidence that this relief is not long-term, with many having surgery several years later for recurrent pain.20 The evidence for conservative therapies completely eradicating all of the symptoms of Morton's neuroma is relatively weak, however, effective non-operative management is the norm.12 If a patient fails conservative measures, surgery may be warranted. Relative contraindications include uncontrolled diabetes, complex regional pain syndrome, and vascular dysfunction.

Operative Treatment

Many surgical methods have been described including 1,12 interdigital nerve excision with intermetatarsal ligament division, isolated intermetatarsal ligament division, and isolated interdigital nerve excision. The patient is usually given regional anesthesia with sedation. A thigh or ankle tourniquet is used to prevent bleeding. The surgical intervention is usually performed with a dorsal approach but can be done from the plantar aspect.

A dorsal incision is made in the interspace between the affected metatarsals. The 3- to 4-cm longitudinal incision is taken down through the skin and subcutaneous tissues. One must take care to identify and retract away the dorsal sensory branch of the intermediate dorsal cutaneous branch of the superficial peroneal nerve.1 Dissection is then bluntly continued down to the level of the intermetatarsal ligament. A small lamina spreader is inserted between the metatarsal heads to facilitate exposure and to place the ligament under tension. A Freer elevator is placed beneath the intermetatarsal ligament and transected with a scalpel or scissors, protecting the underlying neurovascular structures. The neuroma is then identified between the metatarsal heads adherent to the intermetarsal bursa. The neuroma is pulled distally such that the nerve trunk can be divided as proximally as possible with long scissors. The distal branches of the nerve are then dissected. 

Image Removed

Figure 5can be justified empirically, for pain relief. Physical therapy modalities such as ultrasound or electrical stimulation might help but studies demonstrating their effectiveness are lacking. An intermetatarsal injection that perfuses the neurovascular bundle can, with the addition of local anesthetic, help confirmed the diagnosis, and a corticosteroid in the cocktail may help produce more enduring relief.

If a patient fails to improve with the passage of time and non-operative measures, and if all other sources of the pain have been considered and eliminated as diagnostic possibilities, surgery may be indicated.  This treatment involves resecting the nerve proximal to the area of fibrosis.  Another option is the surgical release of the intermetatarsal ligament and removal of scar tissue.   Resecting is thought to be more definitive but cutting the nerve produces toe numbness, so there is some disagreement which operation is best.)

 

Potential operative complications include not only the usual suspects of all foot surgery (delayed healing, infection, deep vein thrombosis to name but three) but in the case of Morton’s neuroma surgery, the persistence of the pain is not rare.  Complex regional pain syndrome (formerly known as reflex sympathetic dystrophy) can appear in rare instances. 

Image Added

Figure . Location of nerve right under the skin (between base of 3rd and 4th toes)

The plantar approach is often used in cases of neuroma recurrence, as it provides better visualization of the proximal nerve trunk, albeit with the risk of a painful plantar scar. A plantar excision is made just proximal to the webspace and extends at least 4 cm proximally. The incision is extended between the metatarsal heads to avoid scarring the bony prominences. Strands of the fibrous plantar tissue must be divided. The neuroma is usually located subcutaneously, and is then resected as described above.

A dorsal approach allows for immediate weight-bearing and suture removal after 2 weeks. A plantar incision delays weight-bearing and suture removal for 2 more weeks.1 A patient usually transitions to a normal shoe by 3-4 weeks, with return to sports in 4-6 weeks.

The most common complication results from wound healing, keloid formation, or superficial infection.3 In one series, 1.1% of patients had a wound infection, while 2.2% had keloid formation over the scar. Recurrent neuroma formation is another complication. This may be the results of inadequate proximal resection of the common digital nerve, but more commonly represents metatarsalgia symptoms from MTP synovitis (or another causes of metatarsalgia) that would not be addressed by the Morton's neuroma surgery. However, typically patients describe high satisfaction rates (80% to 96%) following Morton's neuroma surgery.16,21

Risk factors and prevention

Risk factors include clawing of the lesser toes, an equinus contracture, or tight, ill fitting shoes -anything that will lead to repetitive injury to the Morton's nerve. 

Miscellany

Historically, Morton's neuroma was first described in 1845 by Queen Victoria's surgeon chiropodist, Lewis Durlacher as a "form of neuralgic affection" involving the distal plantar nerves.22 Thirty years later, Thomas G. Morton of Philadelphia described this disorder (incorrectly) as a capsulitis of the 4th metatarsophalangeal joint, although he accurately described the disorder's symptomatology.23 In 1883, Hoadley was the first surgeon to actually excise the interdigital neuroma as a treatment for Morton's neuroma.24 Then in 1940, L.O. Betts confirmed that Morton's neuroma pain was attributed to a swelling of the interdigital nerve.2  Morton's neuroma was named after Thomas G Morton who described the disorder in the 1800, not Dudley Morton who wrote a landmark book entitled  

 

Risk factors and prevention

There are no clear risk factors since the exact etiology of is unknown. Tight ill-fitting shoes and shoes with high heels possibly contribute to the development of Morton’s neuroma and their use should be avoided or at least limited

Miscellany

According to Stigler's Law of Eponymy states that no scientific discovery is named after its original discoverer. Indeed, Stigler's Law was itself ,described with no credit by Robert K. Merton (as the law implies),  This law applies here too in a way: the condition is not named for its original correct discoverer. Although Morton has his name attached to this disorder (by being first to write about the symptoms) it was Betts who first correctly described the pathology. Complicating the eponymy, the Dr. Morton in question was a Thomas Morton, not Dudley Morton, author of the landmark text, "The Human Foot: It's Evolution, Physiology, and Functional Disorders" in 1935.

Key terms 

Medial and lateral plantar nerves, digital nerves, intermetarsal ligament, perineural fibrosis, metatarsalgia

...

Perform a lateral squeeze test and elicit a Mulder’s click, described under patient presentation.

Reference

...

 

...

...