Performing an Ultrasound Guided First MTP Joint Injection

Introduction

The first metatarsophalangeal (MTP) joint is composed of the distal portion of the first metatarsal and the proximal portion of the proximal phalanx (1). Osteoarthritis and bunion pain can affect the first MTP joint and is a common source of pain (2). Patients with first MTP osteoarthritis or hallux rigidus will typically complain of pain and swelling of the first MTP joint (3).

In order to treat the symptoms associated with first MTP osteoarthritis, corticosteroid or platelet rich plasma injections can be performed. This review looks at the technique for performing an ultrasound guided first MTP joint injection.

Procedure

The probe used for the injection can be a 12-4 mHz linear array transducer or a 15-8 mHz hockey stick transducer. The foot will typically be placed flat on the exam table with the patient in a semi-recumbent position (1). A 25g to 27g needle is typically used and the length can vary between 0.75 inch to 1.5 inch needle (1). A total of 1-2mL of injectate are typically used (7).

The injection can be directed in an in plane and out of plane approach. In order to perform the out of plane approach, the probe will be placed in a transverse axis overlying the first MTP joint. A joint effusion can sometimes be seen and it will typically appear as hypoechoic fluid (8). The image below shows the first metatarsal to the left and the proximal phalanx to the right. A joint effusion can be seen as the hypoechoic fluid.

Ultrasound image of the first MTP joint (1)

The needle will then be guided in a medial to lateral or lateral to medial approach (1).

Needle angle for first MTP injection (2)

The injection can also be performed in an in plane long axis approach. The ultrasound can be placed in along axis plane of the first MTP joint. The extensor hallucis longus (EHL) should be identified in long axis with the joint (5).

Ultrasound position for in plane injection (5)

The needle can be guided in plane with the probe into the joint capsule (5). The probe will sometimes need to be moved medially in order to avoid injection of the EHL tendon (5). The image below shows the needle in long axis with the probe.

In plane ultrasound guided first MTP Joint injection (5)

Conclusion

Ultrasound guided injections into the first MTP joint under ultrasound guidance are done to treat symptoms associated with hallux rigidus, osteoarthritis, and gout. Using an ultrasound can improve accuracy and decrease the risk of soft tissue injury (4).

By Gregory Rubin, DO
rubinsportsmed.com

References

1) Kruse, Ryan C., and Brennan Boettcher. “Image-Guided Foot and Ankle Injections.” Foot and Ankle Clinics, vol. 28, no. 3, Sept. 2023, pp. 641–65. PubMed, https://doi.org/10.1016/j.fcl.2023.04.005.

2) Waldman, Steven D., editor. “Copyright.” Atlas of Pain Management Injection Techniques (Fifth Edition), Elsevier, 2023, p. iv. ScienceDirect, https://doi.org/10.1016/B978-0-323-82826-0.12001

4) Reach, John S., et al. “Accuracy of Ultrasound Guided Injections in the Foot and Ankle.” Foot & Ankle International, vol. 30, no. 3, Mar. 2009, pp. 239–42. PubMed, https://doi.org/10.3113/FAI.2009.0239

5) Sahler, Christopher S., et al. “Ultrasound-Guided First Metatarsophalangeal Joint Injections: Description of an in-Plane, Gel Standoff Technique in a Cadaveric Study.” Foot & Ankle Specialist, vol. 6, no. 4, Aug. 2013, pp. 303–06. PubMed, https://doi.org/10.1177/1938640013493465

6) Henning, P. Troy. “Ultrasound-Guided Foot and Ankle Procedures.” Physical Medicine and Rehabilitation Clinics of North America, vol. 27, no. 3, Aug. 2016, pp. 649–71. PubMed, https://doi.org/10.1016/j.pmr.2016.04.005.

7) 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.

8) 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