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Flexor Hallucis Longus Tendon Pain: Is Surgery the Answer?

POSTED ON IN Foot Latest News Ligament/tendon Regenexx-SD Sports Injury BY Chris Centeno

flexor hallucis longus tendon pain

This is a story about Scott, a frustrated runner. One day in 2010 while out for a run, he suddenly heard a snap under his foot. He went from a normal, active life to trying years of different therapies without help. This is his story about how flexor hallucis longus tendon pain almost ruined his life.

What Is the Flexor Hallucis Longus Tendon?

FHL tendonThe flexor hallucis longus (FHL) tendon lives on the bottom of the big toe. I’ve highlighted the tendon in yellow in the picture to the right (click on the image to make it larger). The FHL flexes the toe and along with other tendons also helps to stabilize the ankle. It’s pretty unique in that it has many functions.

plantar plate 2To understand all of Scott’s injuries, you have to understand how the FHL relates to the plantar plate (PP). The PP is a fibrocartilage plate that lives on the bottom of the big toe and other MTP joints. It helps protect the joint from impact forces, like running, similar to the meniscus in the knee. The picture shows how the FHL tendon attaches to the plantar plate just as other foot flexor tendons attach to other plantar plates in other MTP joints.

plantar plate ligamentsFinally, there are ligaments at play here as well. The image to the right shows that there are two ligaments at the side of the toe MTP joints, one that heads downward in red (accessory collateral ligament, or ACL of the toe) and the other in blue (proper collateral ligament, or PCL). For our purposes the ACL is important as it helps to stabilize that plantar plate and hold it in place.

A Runner with Flexor Hallucis Longus Tendon Pain

After feeling sudden pain in the bottom of his foot, Scott’s MRI showed FHL damage as well as small holes in the plantar plates in the second and third MTP joints. In addition to that issue, the first-through-third toe joints (MTPs) began to hurt. MRI also showed evidence of arthritis in his toe joints.

Scott tried a bevy of different treatments over five years, including a PRP injection into the FHL tendon, acupuncture, physical therapy, switching to barefoot, boot immobilization, massage therapy, Motrin, many different kinds of shoes, chiropractic manipulation, electrical stimulation, and ultrasound. In addition, he also saw three foot-and-ankle specialists and was told that he needed surgery. We were literally his last hope.

How Does This Patient’s Problems Showcase Precise Interventional Orthopedics?

I get asked all the time by patients to define what we mean by interventional orthopedics. Take a look at the complexity of the diagrams above of the big toe. Each of these structures—the multiple big toe joints, the plantar plates, the ACL and PCL, the flexor tendons (like the FHL)—is a target for precise, image-guided injections. Even just looking at the FHL alone, you can inject it in the tendon sheath, the tendon itself, or both. In a joint of this size, the difference between placing cells in one structure versus the other is often 1–2 mm (less than 1/16th to 1/32nd of an inch). The knowledge that you need to have to perfect accurately injecting these tiny structures is interventional orthopedics at its best—using ultraprecise, image-guided injections to help patients avoid surgery.

Interventional Orthopedics and Regenexx-SD to the Rescue

I treated the patient with a precisely placed same-day stem cell injection procedure (Regenexx-SD) in March of 2015. The number of physicians in the U.S. who have the level of expertise to place cells with this degree of accuracy using both ultrasound and fluoroscopy and who understand where they need to go, likely numbers less than 100. How did it turn out? This is what we got back from Scott at his one-year registry questionnaire:

“I filled out the form but I also wanted to write in free form that this procedure has improved my condition by 80% after going 4 years without improvement.  It’s been transformative for me.  I can now run again 2–3 days week up to 10 miles with minimal discomfort.  
I am so grateful to Dr. Centeno and the team for giving me the gift to run again.  I’ve mentioned this to literally over one hundred people and no one has heard of this procedure.  If there is a need for a case study or reference, I’d be happy to serve in that capacity to return the favor.”
Enough said, as I think Scott said it all!
The upshot? We’re happy we could help Scott with his flexor hallucis longus tendon pain, toe joint arthritis, and plantar plate injuries! Allowing a runner to get back to running when nothing else has ever helped is a great feeling for a doctor, so thanks to Scott for making my day by letting me know!


    Lucia Pugh says

    Inspiring. I hope I will have a good review of your stem cell bundle of vitamins. Looking forward to less pain.


    Regenexx Team says

    We hope your pain is helped as well!


    Dave says

    Thanks for this informative post. We read so much on knees and shoulder issues, so please keep publishing more on smaller joints such as the foot etc. Question, was there a period of immobilization and/or non-weightbearing after the injection, or relative rest from activity such as from running etc.? What would be the "typical" (or more-often-than-not) post-injection protocol for something like this?


    Regenexx Team says

    Depends on the friability of the tendon (i.e. how damaged it is). For most patients there is no immobilization, but if the tendon proves itself on injection to be highly damaged, a short period of crutches (i.e. 1-3 weeks) may be needed.


    Jamesfilms says

    My wife injured her flexor hallucis longus. She jumped and landed on something dull, right under her bare foot, a child's toy. It's been several months but her pain has not stopped. She cannot run anymore and the doctors just tell her to rest it. We are in central California, who do I contact about this type of procedure?


    Chris Centeno says


    The Regenexx Physician Locator page is set up for you to enter your city and state or zipcode to see what Provider is closest to you. It's important to make sure the Provider treats the area you're seeking treatment for. It looks like the closest to central CA would be Healthlink Medical Center in San Rafael, and they do treat ankles/feet. Here's the link:


    D. Gadd says

    Dear regenexx team, I was in a major MVA and almost had my ankle ripped off. After an unsuccessful surgery to reattach ligaments and screw bones back together I was left with a pedial fracture of the Tib. This led to a complete fusion of the ankle to "help" with pain but only made things worse. Now my FHL is constantly in pain. No one in Canada seems to have any answers other than trying different prescriptions. I don't sleep and hardly walk because of this. Is there anyone in Canada or close to our border that could help, life seems pointless in my current condition.


    Chris Centeno says

    D. Gadd,

    Sorry to hear about your accident! We don't have any Regenexx Providers in Canada yet. Distance depends on where in Canada you are. This patient was treated in Colorado. Please see: and .If you'd like to see if you would be a Candidate, please submit the Candidiate form.


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    About the Author

    Chris Centeno

    Christopher J. Centeno, M.D. is an international expert and specialist in regenerative medicine and the clinical use of mesenchymal stem cells in orthopedics. He is board certified in physical medicine as well as rehabilitation and in pain management through The American Board of Physical Medicine and Rehabilitation.…

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