May 16, 2021

Diagnosis of a Morton’s Neuroma

A Morton’s neuroma is a nonmalignant enlargement of a plantar digital nerve at the level of the metatarsal head (1). The plantar digital nerve can be a branch of the medial or lateral plantar nerve that comes from the tibial nerve (4). Repetitive trauma at the level of the metatarsal head of the plantar digital nerve causes perineural fibrosis and edema of the endoneurium of the nerve (3). In fact, the term neuroma is inaccurate because there is no proliferation of axons with an interdigital neuroma (6). Symptoms of a Morton’s neuroma are forefoot pain and the feeling of ambulating on a pebble (2). These symptoms worsen with ambulation and improve with rest (6).

Case Question

You are evaluating a 31 year old female with insidious onset of foot and toe pain. You are performing a diagnostic sonogram of the affected foot. Which of the following special tests during ultrasound evaluation of the forefoot helps diagnose a Morton’s neuroma?

A) Morton’s maneuver
B) Talar drawer test
C) Dynamic toe extension
D) Pellegrini press

Morton's neuroma nerve anatomy illustration over xray

Image 1. Morton’s neuroma nerve origin (4).

Examination

A Morton’s neuroma should be considered in patients who are middle aged and wear tight fitting shoes (4). They are found more frequently in women (5). Providers should palpate the space between the metatarsal heads for pain (4). Pain can be worse with compression of the intermetatarsal space (4). One commonly used physical exam test for a Morton’s neuroma is a Mulder’s click. The provider will squeeze the metatarsal heads and feel for a palpable click within the interdigital space (1). Morton’s neuromas are most commonly found in the third intermetatarsal space (4). Radiographs are typically not helpful in making the diagnosis of a Morton’s neuroma.

Ultrasound Evaluation

MRI and ultrasound can be used for diagnosis of a Morton’s neuroma. Both imaging modalities are accurate in diagnosis, but an ultrasound is significantly less expensive (2). An ultrasound evaluation for a Morton’s Neuroma involves the use of a linear probe and the probe is placed on the plantar surface of the foot at the level of the metatarsal heads (3). The neuroma can be visualized as a hypoechoic mass between the metatarsal heads and finding posterior acoustic enhancement is also a sign of a Morton’s Neuroma (3,5).

morton neuroma ultrasound

Image 2. Figure of the starting position for ultrasound evaluation (3).

The Mulder’s maneuver can also be used to improve the ultrasound image of a Morton’s neuroma. By applying compression of the metatarsal heads, the Morton’s neuroma may move towards the plantar surface as seen in the image below.

ultrasound mulder maneuver morton's neuroma 2

Image 3. Ultrasound image of a more plantar located Morton’s neuroma after Morton’s maneuver (1).

Conclusion

A Morton’s neuroma is a common source of forefoot pain in patients who wear tight fitting shoes. Ultrasound evaluation is an inexpensive and easy way to diagnose a Morton’s neuroma. Diagnosis is aided with compression of the intermetarsal space with a Mulder compression test. After diagnosis, providers can choose from a wide range of treatment options, ranging from ultrasound guided injections to surgical removal.

Case Conclusion

Correct Answer: A. Morton’s Neuroma can be found as a hypoechoic mass within the intermetatarsal space. They are most commonly found in the third intermetatarsal space. A Mulder’s maneuver involves compression of the intermetatarsal space that helps bring the Morton’s Neuroma towards the plantar surface.

Ata, Ayşe Merve, et al. “Ultrasound-Guided Diagnosis and Treatment of Morton’s Neuroma.” Pain Physician, vol. 19, no. 2, Feb. 2016, pp. E355-358.

References

  1. Gimber, Lana H., et al. “Ultrasound Evaluation of Morton Neuroma Before and After Laser Therapy.” AJR. American Journal of Roentgenology, vol. 208, no. 2, Feb. 2017, pp. 380–85. PubMed, doi:10.2214/AJR.16.16403.
  2. Bignotti, Bianca, et al. “Ultrasound versus Magnetic Resonance Imaging for Morton Neuroma: Systematic Review and Meta-Analysis.” European Radiology, vol. 25, no. 8, Aug. 2015, pp. 2254–62. PubMed, doi:10.1007/s00330-015-3633-3.
  3. Ata, Ayşe Merve, et al. “Ultrasound-Guided Diagnosis and Treatment of Morton’s Neuroma.” Pain Physician, vol. 19, no. 2, Feb. 2016, pp. E355-358.
  4. Mak, M. S., et al. “Morton’s Neuroma: Review of Anatomy, Pathomechanism, and Imaging.” Clinical Radiology, vol. 76, no. 3, Mar. 2021, p. 235.e15-235.e23. PubMed, doi:10.1016/j.crad.2020.10.006.
  5. Torriani, Martin, and Susan V. Kattapuram. “Technical Innovation. Dynamic Sonography of the Forefoot: The Sonographic Mulder Sign.” AJR. American Journal of Roentgenology, vol. 180, no. 4, Apr. 2003, pp. 1121–23. PubMed, doi:10.2214/ajr.180.4.1801121.
  6. Grear, Benjamin. “Neurogenic Disorders”. Campbell’s Operative Orthopaedics. Jan 2021.

By: Gregory Rubin

Rubinsportsmed.com

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