Physical Medicine and Rehabilitation for Morton Neuroma

Interdigital nerves are composed of communicating branches from the lateral and medial plantar nerves. At the level of the metatarsal heads, the interdigital nerve traverses inferior to the intermetatarsal ligament. At this site, the nerve may be compressed or stretched from repetitive toe flexion and extension. Other studies have shown perineural fibrosis and demyelination at the level of the metatarsal heads, indicating that the damage in Morton's neuroma may be more distal than the intermetatarsal ligament.[11]

Frequency

United States

Morton's neuroma is a common disease entity of the foot.

International

The incidence of Morton's neuroma is presumed to be the same internationally as in United States.

Sex

The female-to-male ratio for Morton's neuroma is 5:1.

Age

The highest prevalence of Morton's neuroma is found in patients aged 15-50 years, but the condition may occur in any ambulatory patient.

Obtaining an accurate history is important to making the diagnosis of Morton's neuroma. Possible reported findings provided by the patient with Morton's neuroma include the following:

• The most common presenting complaints include pain and dysesthesias in the forefoot and corresponding toes adjacent to the neuroma.

• Pain is described as sharp and burning, and it may be associated with cramping.

• Numbness often is observed in the toes adjacent to the neuroma and seems to occur along with episodes of pain.

• Pain typically is intermittent, as episodes often occur for minutes to hours at a time and have long intervals (ie, weeks to months) between a single or small group of multiple attacks.

• Some patients describe the sensation as "walking on a marble."

• Massage of the affected area offers significant relief.

• Narrow, tight high-heeled shoes aggravate the symptoms.

• Night pain is reported but is rare.

Many sources acknowledge that the examination of patients with Morton's neuroma frequently is negative. However, studies have shown that a clinical history and examination may be more sensitive than ultrasonography or magnetic resonance imaging (MRI).[6, 12] Most often, sensation is wholly intact and maneuvers are unsuccessful in reproducing the characteristic pain. Palpation of the actual neuroma seldom is successful. Most clinicians focus on the history and on the lack of additional findings that might suggest other disorders.

• Firm squeezing of the metatarsal heads with one hand while applying direct pressure to the dorsal and plantar interspace with the other hand may elicit radiating neuropathic pain. Pain localized only to the plantar aspect of the webspace also may be consistent with Morton's neuroma.

• The squeeze test may also result in a "click" (Mulder click) as the neuroma moves between the metatarsals in the dorsal direction.[13]

• Passive and active toe dorsiflexion may aggravate symptoms.

• Sensory abnormalities may be observed, although motor deficits are not consistent with an interdigital neuroma because these are sensory nerves exclusively. Weakness would raise concerns for another diagnosis.

• Careful palpation of the metatarsal heads and shafts may help to differentiate stress fractures or metatarsal head osteonecrosis from Morton's neuroma.

• Palpation of the tarsometatarsal joint and metatarsophalangeal (MTP) joints may reveal tenderness, indicating midfoot arthritis or metatarsalgia (eg, when the tenderness is primarily on the plantar surface only) or MTP synovitis (eg, when the joint is tender with palpation).

• Pain from MTP synovitis is aggravated with forced toe flexion. Subtle joint swelling also may coexist with MTP synovitis. Tenderness localized to the second MTP joint, along with swelling and warmth, may be, in rare cases, an early presentation of Freiburg osteochondrosis.

• Inspection of the foot and evaluation of foot and ankle mechanics should be performed as part of the physical examination, looking for callus formation, hallux valgus, first-ray flexibility, hyperpronation, integrity of the medial arch, and gastrocnemius-soleus flexibility.

Various factors have been implicated in the precipitation of Morton's neuroma.

• Morton's neuroma is known to develop as a result of chronic nerve stress and irritation, particularly with excessive toe dorsiflexion.

• Poorly fitting and constricting shoes (ie, small toe box) or shoes with heel lifts often contribute to Morton's neuroma. Women who wear high-heeled shoes for a number of years or men who are required to wear constrictive shoe gear are at risk.

• A biomechanical theory of causation involves the mechanics of the foot and ankle. For instance, individuals with tight gastrocnemius-soleus muscles or who excessively pronate the foot may compensate by dorsiflexion of the metatarsals subsequently irritating of the interdigital nerve.

• Certain activities carry increased risk of excessive toe dorsiflexion, such as prolonged walking, running, squatting, and demi-pointe position in ballet.[13]

See the History and Pathophysiology sections.

No laboratory studies are indicated for the diagnosis of Morton's neuroma.

Results of plain films are normal in Morton's neuroma.

Ultrasonography is gaining in popularity and may be equivalent in sensitivity to MRI in detecting Morton's neuroma.[6, 7, 8]  Indeed, a literature review by Bignotti et al indicated that ultrasonography and MRI are equally accurate for the diagnosis of Morton neuroma, with the modalities having sensitivities of 0.91 and 0.90, respectively.[14]

Computed tomography (CT) scanning has been used but may not be as sensitive as MRI or ultrasonography. MRI, while not needed in most cases for establishing diagnosis of Morton's neuroma, has been studied widely.[4, 5] Sensitivity of 87% and specificity as high as 100% have been reported. Asymptomatic neuromas may occur and confound accurate diagnosis.

Indications exist that Morton's neuromas smaller than 5 mm in diameter may not be significant clinically and that other diagnoses may be excluded carefully before such a small lesion is diagnosed as a symptomatic Morton's neuroma. Imaging with T1 weighting in a coronal plane is recommended for best visualization. In addition, on T2 imaging, the low signal of a Morton's neuroma may help to differentiate it from a true neuroma, ganglion cyst, or intermetatarsal bursal fluid collection.

Contrast enhancement usually is demonstrated with Morton's neuromas.

Electromyography and nerve conduction study (EMG/NCS) of Morton's neuroma are not used often because of the technical difficulty in performing them; needle stimulation of the common digital nerve and pickup on the adjacent toe or toes, which may be of short distance, is required. Surface stimulation results most often in volume conduction through the skin to the pickups because of the short distance involved and the large amount of stimulation needed to penetrate the deep tissue separating the nerve from the skin surface.

Temporary elimination of pain and numbness in the associated webspace by a common digital nerve block with an anesthetic agent supports a diagnosis of Morton's neuroma. If numbness of the associated webspace occurs but no decrease in pain is noted, other diagnoses should be considered.

Tissue biopsy is neither needed nor recommended for Morton's neuroma.

Physical Therapy

Treatment strategies for Morton's neuroma range from conservative to surgical management. The conservative approach to treating Morton's neuroma may benefit from the involvement of a physical therapist. The physical therapist can assist the physician in decisions regarding the modification of footwear, which is the first treatment step. Recommend soft-soled shoes with a wide toe box and low heel (eg, an athletic shoe). High-heeled, narrow, nonpadded shoes should not be worn, because they aggravate the condition.

The next step in conservative management is to alter alignment of the metatarsal heads. One recommended action is to elevate the metatarsal head medial and adjacent to the neuroma, thereby preventing compression and irritation of the digital nerve. A plantar pad is used most often for elevation. Have the patient insert a felt or gel pad into the shoe to achieve the desired elevation of the above metatarsal head.

Other possible physical therapy treatment ideas for patients with Morton's neuroma include cryotherapy, ultrasound, deep tissue massage, and stretching exercises. Ice is beneficial to decrease the associated inflammation. Phonophoresis also can be used, rather than just ultrasound, to further decrease pain and inflammation.

When conservative measures for Morton's neuroma are unsuccessful, surgical excision of the area of fibrosis in the common digital nerve (as demonstrated in the images below) may be curative. Common adverse outcomes include dysesthesias radiating from a painful nerve stump after surgical excision of the Morton's neuroma. Dysesthesias may be treated as any other dysesthetic pain. (See Medication.)[15, 16, 17, 18, 19, 20]

Surgical options include the following:

• Neurectomy with nerve burial[21, 22, 23]

• Transverse intermetatarsal ligament release, with or without neurolysis

• Endoscopic decompression of the transverse metatarsal ligament

A dorsal surgical approach may decrease recovery time,[24]  although a study by Kundert et al indicated that a longitudinal plantar approach to excision of Morton neuroma is also effective, providing strong pain relief;[25]  a study by Habashy et al found comparable outcomes and patient satisfaction with either a plantar (17 patients) or dorsal (20 patients) approach to neurectomy for Morton neuroma.[26, 27]

Neurectomy: typical incision location.

Neurectomy: superficial exposure.

Neurectomy: deeper dissection.

Neuroma and adherent fibrofatty tissue.

A study by Reichert et al of the long-term outcomes of dorsal neurectomy indicated that this remains a useful treatment for Morton neuroma, despite the existence of other, less-invasive therapeutic techniques. The study, which involved 41 patients and had an average follow-up time of 7.4 years, found that the mean American Orthopaedic Foot and Ankle Society (AOFAS) score rose from 39.4 (preoperatively) to 83.4 (postoperatively), while the mean visual analog scale score fell from 7.04 (preoperatively) to 1.4 (postoperatively). The report also determined that the best results were obtained in patients with single neuromas over 3 mm in size and resected within 12 months of symptom onset.[28]

A retrospective study by Lee et al suggested that treatment of Morton’s neuroma with a sliding osteotomy on the proximal metatarsal bone can be a relatively effective means of pain relief. The investigators reported improvements in the AOFAS Lesser Metatarsophalangeal-Interphalangeal Scale and Foot Function Index scores, from 52.1 and 62.4, respectively, preoperatively, to 74.2 and 31.3, respectively, postoperatively.[29]

If surgical intervention is needed for Morton's neuroma, consultation with an orthopedic surgeon specializing in foot and ankle surgery is recommended.

Corticosteroid injections

Another treatment approach involves injection of the Morton's neuroma.[9, 10] Perform injection into the dorsal aspect of the foot, 1-2 cm proximal to the webspace, in line with the MTP joints. Advance the needle through the mid-webspace into the plantar aspect of the foot until the needle gently tents the skin. Then withdraw it about 1 cm to where the tip of the neuroma is located. Inject a corticosteroid/anesthetic mix. A reasonable volume is 1 mL of corticosteroid and 2 mL of anesthetic. The anesthetic used should not contain epinephrine, as necrosis may result. Care also should be taken not to inject into the plantar pad.[30]

Studies indicate that a dorsal approach may decrease patient discomfort.[31]

Adverse outcomes from corticosteroid injection include plantar fat pad necrosis. Transient numbness of the toes also may occur. Although many practitioners use multiple injections, the likelihood of benefit from subsequent injections, after failure to achieve relief from the initial injection, is negligible.

An Australian investigation using a single, ultrasonographically guided corticosteroid injection for Morton's neuroma found that 9 months after treatment, complete pain relief had occurred in 11 of the 39 neuromas studied.[32]

A literature review by Edwards et al indicated that in adults with Morton’s neuroma, short- to medium-term pain benefits can be derived from a single corticosteroid injection, with the rate of ensuing adverse events being low;[33] a study by Hau et al found that at a mean 4.8-year follow-up, a single corticosteroid injection remained effective in 38% of Morton’s neuromas.[34] However, Edwards and colleagues found that while the injection was apparently superior to usual care, it was not clear whether it was superior to local anesthetic alone, and it showed inferiority to surgical excision.[33]

A study by Lizano-Díez et al found no additional pain-relief benefit to injections combining a corticosteroid with a local anesthetic compared with those using a local anesthetic alone, in patients with Morton’s neuroma. Patients in the study received three injections, with the investigators determining at 3- and 6-month follow-up that patients who received the corticosteroid/anesthetic combination did not significantly differ from the anesthetic-only patients with regard to improvement in pain and function.[35]

A study by Park et al indicated that in patients who receive corticosteroid injection for treatment of Morton’s neuroma, the sole ultrasonographic predictor of treatment failure is the size of the neuroma, with the parameters of intermetatarsal distance and the proportion of neuroma in the intermetatarsal space being prognostically insignificant. The investigators found that failure occurred in patients with a mean neuroma size of 7.9 mm, while treatment was successful in the group with a mean neuroma size of 5.5 mm.[36]

Extracorporeal shockwave therapy

Fridman et al investigated the efficacy of extracorporeal shockwave therapy in the treatment of Morton's neuroma. The study included 23 patients who, after more than 8 months of conservative therapy, had a visual analog scale (VAS) pain score of at least 4. In the study, 13 patients were treated with shockwave therapy, with the rest receiving a sham treatment. By 12-week posttreatment follow-up, members of the shockwave treatment group showed a significant reduction in their VAS pain score, whereas patients in the sham treatment group did not. The authors concluded that extracorporeal shockwave therapy may be an effective alternative to surgical excision in the treatment of Morton's neuroma.[37]

Radiofrequency ablation

A further nonsurgical option includes thermoneurolysis with percutaneous radiofrequency ablation. This method heats the nerve with radiofrequency to the point of neurolysis and may be as effective as surgical intervention.[38]

Dysesthesias may be treated as any other dysesthetic pain. Tricyclic antidepressants, such as amitriptyline at 10-25 mg PO qhs, may be tried. If this approach is unsuccessful, anticonvulsants (eg, gabapentin, carbamazepine) often are effective.

Class Summary

A complex group of drugs that have central and peripheral anticholinergic effects, as well as sedative effects. They have central effects on pain transmission, and they block the active re-uptake of norepinephrine and serotonin.

Amitriptyline (Elavil)

Analgesic for certain chronic and neuropathic pain. Low doses, 10-25 mg qhs, may provide pain relief from burning and tingling occurring at rest but function only as an adjunct to definitive treatment.

Class Summary

Use of certain antiepileptic drugs (AEDs), such as the GABA analogue Neurontin (gabapentin), has proven helpful in some cases of neuropathic pain. Thus, although unstudied, a trial of such an agent might conceivably provide analgesia for symptomatic neuropathy. Used for dysesthesias not controlled with definitive treatment plus tricyclic antidepressants (or in patients unable to take tricyclic antidepressants).

Gabapentin (Neurontin)

Neuromembrane stabilizer useful in pain reduction with dysesthetic pain. Has antineuralgic effects; however, exact mechanism of action is unknown. Structurally related to GABA, but does not interact with GABA receptors.

Pregabalin (Lyrica)

Structural derivative of GABA. Mechanism of action unknown. Binds with high affinity to alpha2-delta site (a calcium channel subunit). In vitro, reduces calcium-dependent release of several neurotransmitters, possibly by modulating calcium channel function. FDA approved for neuropathic pain associated with diabetic peripheral neuropathy or postherpetic neuralgia and as adjunctive therapy in partial-onset seizures.

Class Summary

These agents inhibit neuronal serotonin and norepinephrine reuptake.

Duloxetine (Cymbalta)

Description Indicated for diabetic peripheral neuropathic pain. Potent inhibitor of neuronal serotonin and norepinephrine reuptake.

General prevention includes ensuring that shoes fit properly. Recommend that the patient wear well-padded, low-heeled shoes with a wide toe box. No other preventative techniques are recommended.

Chronic pain may develop when treatment is unsuccessful for patients with Morton's neuroma. Postoperative complications, such as dysesthesias, are possible when surgery is performed to remove the neuroma. Possible complications following corticosteroid injections may include plantar fat pad necrosis and transient numbness of the toes.

Prognosis for recovery is good with conservative treatment; however, patients still may require surgical intervention.[39] Some patients who undergo surgery report a recurrence rate of as high as 50%.

Patients should be well informed about proper footwear.