Mortons Neuroma Injection

Other Names

• Mortons Neuroma Injection
• Ultrasound Guided Morton's Neuroma Injection
• Palpation Guided Morton's Neuroma Injection

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Background

The first, second, and third common plantar digital nerves arise from the medial plantar nerve, while the fourth nerve arises from the lateral plantar nerve. The third nerve often receives a communicating branch (white arrow). Each common plantar digital nerve divides into two proper plantar digital nerves. Morton’s neuromas occur at the bifurcation of the common plantar digital nerve.

Key Points

• Use a high frequency, linear probe
• 25 to 27-guage, 1-1.5 inch needle
• Dorsal approach is preferred

Anatomy

• Interdigital nerve between 3rd and 4th metatarsophalangeals
• Forms from a coalescence of:
  • Far lateral branch of the medial calcaneal nerve
  • Medial branch of the lateral calcaneal nerve
• Can develop into symptomatic fibrous nodule (i.e. Mortons Neuroma)
• Less commonly, can occur between 2nd and 3rd MTP

Ultrasound vs Palpation Guidance

• Santiago et al: Compared to a blind injection, ultrasound guidance provides a statistically significant improvement at some stages of the follow-up (45 days, 2 and 3 months)

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Indications

• Mortons Neuroma

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Contraindications

• Absolute
  • Anaphylaxis to injectates
  • Overlying cellulitis, skin lesion or systemic infection
• Relative
  • Can be treated with less invasive means
  • Hyperglycemia or poorly controlled diabetes
  • Lack of symptom improvement with previous injection

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Procedure

Ultrasound imaging of Morton’s neuroma. A: Clasping of the forefoot in the short axis view; B, C: Short axis views of the intermetatarsal space before (B) and after (C) squeezing the forefoot; D: Clasping of the forefoot in the long axis view; E, F: Long axis views of the intermetatarsal space before (E) and after (F) squeezing the forefoot. In all images, arrows indicate Morton’s neuroma

Plantar approach with ultrasound position in short axis

Plantar approach with transducer rotated into long axis

Dorsal approach with ultrasound position in short axis

Dorsal approach with ultrasound position in long axis

(a)Blind injection in Morton’s neuroma. (b)Morton’s neuroma (MN) injection under ultrasound guidance using dorsal approach. (c)In ultrasound-guided injection the tip of the needle is advanced between the MN and the bursa distributing the injectate around the MN (d)

Equipment

• Sterile prep (including chloraprep, chlorhexadine, iodine, etc)
• Ultrasound with sterile probe cover
• Gloves
• Needle
  • Local anesthesia: typically 23-25 gauge, 1.5 inch
  • Injection: 25-27 gauge, 1-1.5 inch needle
• Syringe: 5-10 mL
• Gauze
• Ethyl Chloride
• Bandage
• Injectate
  • Local anesthetic
  • Corticosteroid/ injectate

Ultrasound Findings

• Best evaluated using a superficial linear transducer
• Hypoechoic mass greater than 5 mm measured in short axis is usually found in symptomatic Morton’s neuroma
• Long axis view:
  • Neuroma has a more fusiform appearance
  • Can see continuity of the neuroma with the interdigital nerve (somewhat oblique to the nearby metatarsal bone)
• Sonographic Tinels Sign
  • Squeeze the neuroma between the transducer and the operator’s opposite thumb.
  • Positive test: reproduction of pain and/or paresthesias
• If having trouble finding the nerve
  • Color Doppler Can be used to help find nerve, Interdigital artery runs adjacent to it
  • Mulder's Click Test, in which the metatarsal heads are squeezed together, can also help identify the nerve
• Don't confuse with intermetatarsal bursitis

Plantar Approach: Long Axis, In Plane

• Patient Position
  • Prone
  • Foot at position that is at comfortable height for practitioner performing injection
• Probe Position, Needle Orientation
  • Start in short axis
  • Once the needle is in the neuroma, turn the probe in long axis
  • Needle is in plane
  • Needle approach is distal-to-proximal
• Target
  • Hyper- to hypoechoic to anechoic nodule at the level of the intermetatarsal space
• Pearls and Pitfalls
  • Distinguish from intermetatarsal bursitis where the anechoic fluid is usually compressible
  • Distinguish from metatarsalgia by direct palpation of the metatarsal joints
  • Note that these three conditions can co-exist in the same patient

Dorsal Approach: Long Axis, In Plane

• Patient Position
  • Supine
  • Knee flexed, forefoot hanging off end of examination table
  • Foot at position that is at comfortable height for practitioner performing injection
• Probe Position, Needle Orientation
  • Start in short axis
  • Once the needle is in the neuroma, turn the probe in long axis
  • Needle is in plane
  • Needle approach is distal-to-proximal
• Target
  • Hyper- to hypoechoic to anechoic nodule at the level of the intermetatarsal space
• Pearls and Pitfalls
  • Distinguish from intermetatarsal bursitis where the anechoic fluid is usually compressible
  • Distinguish from metatarsalgia by direct palpation of the metatarsal joints
  • Note that these three conditions can co-exist in the same patient

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Aftercare

• No major restrictions in most cases
• Can augment with ice, NSAIDS

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Complications

• Skin: Subcutaneus fat atrophy, skin atrophy, skin depigmentation
• Painful local reaction
• Infection
• Hyperglycmia
• Tendon, nerve or blood vessel injury

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See Also

• Procedures Main
• Ultrasound Main
• Foot Pain Main

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