A Guide To Endoscopic Decompression For Intermetatarsal Neuromas

Author(s): 
Michael M. Fanous, DPM, MHA, MS

   The differential diagnosis of Morton’s neuroma includes:
* metatarsal stress fracture
* rheumatoid arthritis
* osteochondritis dissecans or Freiberg’s infraction
* localized vasculitis
* ischemia
* tarsal tunnel syndrome
* nerve root compression syndromes
* peripheral neuritis
* peripheral neuropathy
* intermetatarsal bursitis

   Radiographs. Obtain weightbearing radiographs in order to rule out bony abnormality.

   Sensory nerve conduction study. Electrodiagnostic techniques are not very accurate. This is primarily due to difficulty in isolating a single interdigital nerve with an electrode to measure sensory conduction velocity.

   Magnetic resonance imaging (MRI). Magnetic resonance imaging is very useful in differentiating Morton’s neuroma mass from adjacent surrounding bone and soft tissues.

Pertinent Insights On The Etiology Of Morton’s Neuroma And Biomechanics

Researchers have proposed many theories for the etiology of Morton’s neuroma.1,3 Histological findings leave little doubt that the syndrome is indeed a mechanical entrapment neuropathy. The deep transverse intermetatarsal ligament appears to be the anatomic structure against which most of this entrapment occurs. The majority of intermetarasal neuromas occur in the pronated foot, where there are not only excessive stretch forces imposed on the interdigital nerves but also compressive and shearing forces form the adjacent hypermobile metatarsal heads.

   As the medial and lateral plantar nerves pass along the medial side of the foot, they dive plantarly under the arch. Stress occurs on these nerves during prolonged midstance pronation as the foot everts, abducts and dorsiflexes. Tension increases as these nerves travel around the flexor digitorum brevis sling and draw up tightly against the plantar and anterior edge of the unyielding deep transverse intermetatarsal ligament. Further tension and compression occur at this ligament when the toes hyperextend at the metatarsophalangeal joint. Thus, occupations requiring repetitive toe hyperextension can result in the development of an intermetatarsal neuroma, regardless of foot type.

   Finally, pointed toe or narrow shoes can further add pressive forces that favor the production of intermetatarsal neuromas, regardless of foot type. High-heeled shoes throw weight forward onto the ball of the foot, jamming it into the narrow front of the shoe. These shoes will also force the toes into hyperextension and thus contribute to the etiology.

A Guide To Surgical Management

When physicians have exhausted conservative treatment without relief of pain, surgical intervention is indicated.

   One option for neuroma management is endoscopic decompression of intermetatarsal neuroma. The surgeon would place the patient on the operating table in the supine position. After ensuring appropriate anesthesia, one would prep and drape the affected foot in the appropriate fashion. Apply a thigh or ankle tourniquet. Inflate it to 250 to 300 mmHg of pressure after appropriate elevation and exsanguination utilizing an Esmarch bandage.

   Mark the affected interspace to ensure proper cannular placement. Place a longitudinal line over the dorsal aspect of the interspace between the respective metatarsal heads from proximal to distal. Palpate the metatarsal heads and place a dorsal incision approximately 2.5 cm proximal to the level of the metatarsophalangeal joint.

Comments

Great paper! I have been doing decompressions for Morton's entrapment for 12 years now and definitely have seen the results of patients pain relief from this procedure. We should acknowledge Stephen L. Barrett, DPM, who developed this procedure and surgical pictures you have used in your paper. Dr. Barrett is sited numerous times in the literature for his work on this condition and procedure. Thanks to Dr. Barrett for thinking outside the box on this condition and understanding the pathophysiology of a true nerve entrapment ( not a neuroma). I am sure I speak for many surgeons who were trained in this procedure and see the results firsthand.

I agree with Dr. Rascon that Dr Barrett's work and pictures should be acknowledged in this paper as a professional courtesy.

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