Performing an Ultrasound Guided Morton’s Neuroma Injection
Introduction
The terminal branch of the medial or lateral plantar nerve is known as the interdigital nerve and is found between the metatarsal heads and transverse intermetatarsal ligament (1,4). Compression and traction of the interdigital nerve can lead to fibrous enlargement of the nerve, which is referred to as a Morton’s neuroma (1,2). This process typically occurs within the second and third intermetatarsal webspace (2).
Figure 1 shows the transverse ligament (red arrows) overlying the neurovascular bundle below (9)
The symptoms associated with a neuroma include pain that localizes to the metatarsal heads, forefoot burning, and interdigital pain that worsens with walking and standing (1). Patients may also feel like they are walking on a stone or pea in their shoe (2). This review will focus on how to perform an ultrasound guided injection for the treatment of symptoms associated with a Morton’s neuroma.
Figure 1 showing an ultrasound image of the hypoechoic Morton’s neuroma
Procedure
When visualizing a Morton’s neuroma with an ultrasound, the provider is looking for an anechoic or hypoechoic neuroma between the metatarsal heads (2). A Mulder’s maneuver applies compression of the metatarsal heads and can make visualization easier (2).
Figure 2 showing the starred anechoic neuroma (2)
One injection approach involves the patient being placed in the supine position with the knee of the affected side flexed to 45 degrees (1). A rolled up towel can be placed under the forefoot to aid in opening up space between the metatarsal heads (1). Then, a linear 12-4 MHz transducer is placed on the dorsum surface of the foot overlying the metatarsal heads (1). A 25g needle can be visualized as it is inserted into the space in and around the neuroma (1).
Figure 3 showing the interdigital injection with u/s probe in sagittal plane (8)
When performing the injection from the dorsal aspect of the foot, it is important to visualize the needle through the superficial transverse metatarsal ligament as direct injection into the ligament with corticosteroids can lead to ligament rupture (3).
Figure 4 showing a schematic of the dorsal approach (7)
A dorsal approach for the injection can also be performed with the knee in extension (5). With the heel flat on the table, the probe can be placed either on the dorsal or plantar surface of the foot (5). In the image below, the needle is placed on the dorsum of the foot to avoid injectate into the plantar surface, which can lead to atrophy (5).
Figure 5 showing needle angle from a dorsal approach (5)
Another approach would have the patient supine and the knee kept straight allowing the heel to be flat on the surface of the table (2). A 12-4 MHz transducer can then be placed on the plantar surface of the foot at the level of the metatarsal heads (2). An in-plane injection can then be performed using a 25g needle (2). An image of the in-plane approach is seen below.
Figure 6 is an in-plane approach to inject the Morton’s neuroma (2)
Conclusion
Ultrasound guided injections of the interdigital nerve at the level of the metatarsal heads can be performed for treatment of a Morton’s neuroma. Multiple injection routes exist, but the consensus typically involves directing the needle from the dorsum of the foot to avoid plantar forefoot atrophy. Ultimately, providers need to find a route that they are comfortable with and be willing to adapt based on the patient’s anatomical features.
By Gregory Rubin, DO
rubinsportsmed.com
– More Foot Pain @ Sports Med Review: https://www.sportsmedreview.com/by-joint/foot/
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– Morton’s Neuroma Injection @ Wiki Sports Medicine: https://wikism.org/Mortons_Neuroma_Injection
References
1) Pasquali, Cecilia, et al. “Ultrasound-Guided Alcohol Injection for Morton’s Neuroma.” Foot & Ankle International, vol. 36, no. 1, Jan. 2015, pp. 55–59. PubMed, https://doi.org/10.1177/1071100714551386
2) 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
3) Santiago, Fernando Ruiz, et al. “Long-Term Comparison between Blind and Ultrasound-Guided Corticoid Injections in Morton Neuroma.” European Radiology, vol. 32, no. 12, Dec. 2022, pp. 8414–22. PubMed, https://doi.org/10.1007/s00330-022-08932-y.
4) Drakonaki, Eleni E., et al. “Ultrasound-Guided Intervention in the Ankle and Foot.” The British Journal of Radiology, vol. 89, no. 1057, 2016, p. 20150577. PubMed, https://doi.org/10.1259/bjr.20150577
5) Ruiz Santiago, Fernando, et al. “Ultrasound Guided Injections in Ankle and Foot.” Journal of Ultrasound, July 2023. PubMed, https://doi.org/10.1007/s40477-023-00808-1.
6) Yablon, Corrie M. “Ultrasound-Guided Interventions of the Foot and Ankle.” Seminars in Musculoskeletal Radiology, vol. 17, no. 1, Feb. 2013, pp. 60–68. PubMed, https://doi.org/10.1055/s-0033-1333916
7) Klontzas, Michail E., et al. “Ultrasound-Guided Treatment of Morton’s Neuroma.” Journal of Ultrasonography, vol. 21, no. 85, June 2021, pp. e134–38. PubMed, https://doi.org/10.15557/JoU.2021.0022.
8) Markovic, Maja, et al. “Effectiveness of Ultrasound-Guided Corticosteroid Injection in the Treatment of Morton’s Neuroma.” Foot & Ankle International, vol. 29, no. 5, May 2008, pp. 483–87. PubMed, https://doi.org/10.3113/FAI-2008-0483
9) Nieves, Gabriel Camunas, et al. “Anatomic Basis for a New Ultrasound‐guided, Mini‐invasive Technique for Release of the Deep Transverse Metatarsal Ligament.” Clinical Anatomy, vol. 34, no. 5, July 2021, pp. 678–84. DOI.org (Crossref), https://doi.org/10.1002/ca.23692
