Foot & Ankle

Flexor Hallucis Longus Pain – Anatomy, Diagnoses, and Treatment

By August 22, 2019 September 16th, 2019 No Comments

The flexor hallucis longus is one of a group of deep muscles in the lower leg and foot. This particular muscle is prone to injury and degeneration due to its location, application, and daily use.

Flexor hallucis longus pain is known to reduce mobility and may at times become paralyzing due to the severity of discomfort experienced by those who suffer from it.

In this article we will explore what causes flexor hallucis longus pain, how it is diagnosed, conventional treatment options, and new advancements in regenerative medicine which may be applicable for treating this degenerative illness.

Anatomy of the Flexor Hallucis Longus

The flexor hallucis longus is a muscle which is nested in the back of the leg and is covered by several other muscle groups. It shouldn’t be a surprise that it is part of the “deep muscle” group of the posterior compartment of the leg. The group surrounding this group of deep muscle is known as the “superficial muscle group” and helps to insulate the softer muscles nested inside.

The flexor hallucis longus is responsible for flexing the joints of the big toe. To help accomplish these bends and allow you to perform other functions, the flexor hallucis longus needs a nerve supply. Nerves direct signals from the brain to help stimulate muscle movement. For the flexor hallucis longus, this supply of synapses comes from the tibial nerve – a nerve which weaves from the upper back portion of the knee, all the way down to the base of the foot and the big toe.

With muscles such as the flexor hallucis longus, it would be appropriate to say that most of the time, form follows function – if we know where the muscle begins and ends, we can deduce what it does. For the flexor hallucis longus, the beginning is along the fibula, a long, thin and lateral bone in the lower leg. It keeps running along the fibula and connects to the bottom portion of the other lower leg bone, the tibia. Finally, it travels through small grooves in the bones at the back of the foot and ankle and ends as a tendon at the base of the big toe.

By weaving around the ankle and base of the foot, the flexor hallucis longus and its tendon function as a sort-of pulley system which contracts and relaxes to provide movement to the big toe and the force to push off from the base of the foot. This intricate weave of tendon and muscle is a common source of pain due to the abnormal compression and stress which is placed on it in daily movement.

Flexor Hallucis Longus Pain Contributing Factors

By interacting with its tendon counterpart and the joints of the foot, the flexor hallucis longus is able to provide movement by pushing the force of the rear foot all the way to the big toe. Overtime, the muscle and tendon of the flexor hallucis longus can begin to develop pain due to a number of reasons. Some of the most common contributing factors for flexor hallucis longus pain are:

  • Past injury
  • Repetitive exertion
  • Hyper extension
  • Muscle tears
  • Bone constriction
  • Weak blood flow
  •  Abnormal healing after injury

Because of the mechanics which lead to the onset of flexor hallucis longus pain, it is most prevalent in athletic populations. Flexor hallucis longus pain is so common amongst athletes that these types of injuries have come to be known as “dancers tendonitis” due to their extreme prevalence in classic ballet dancers. This isn’t to say that it isn’t common amongst athletes in other sports. Swimmers, footballers, gymnasts, sprinters, and anyone who repetitively pushes off from the base of their big toe can also suffer from dancer’s tendonitis and general flexor hallucis longus pain.

Signs and Symptoms of Flexor Hallucis Longus Pain

Ailments associated with the flexor hallucis longus and its tendon are typically characterized by pain at the inner side of the ankle. These pains are usually made worse by jumping, landing, or pointing the foot. A person suffering from dancer’s tendonitis may feel an abnormal crackling or popping stemming from the joints in the path of the flexor hallucis longus. This crackling and popping may be faint or loud enough for others to hear and is often accompanied by crunching sensations which may become uncomfortable or painful overtime. If the symptoms escalate, they may lead to an inability to relax the big toe resulting in a feeling of the big toe being stuck in flexion.

Other common signs of flexor hallucis longus damage include:

  • Pain associated with forefoot push off
  • Pain underneath the arch of the foot or at the base of the big toe
  • Swelling of the ankle
  • Pain linked to movement of the big toe

These signs and symptoms are only a base for the diagnosis of flexor hallucis longus pain, the only way to be certain that there is any damage is to set up a professional clinical screening.

Diagnosis of Flexor Hallucis Longus Pain

A clinical examination of a suspected flexor hallucis longus injury includes an inspection of the areas surrounding this muscle and tendon pair. The regions which yield the most insight into the injury include the back and inner side of the ankle, the underside of the foot, and the sesamoids (bones before the base of the big toe).

First, an examiner will ask the patient to extend the foot to ensure that the flexor hallucis longus is under tension. Next, the examiner will begin to feel for abnormalities in the aforementioned regions, an act known as palpation. By massaging these portions of the foot while the flexor hallucis longus is under strain, an examiner can get an idea of the epicenter of the pain. Typically, an examiner will look for tenderness in specific locations of the foot or while the foot is under specific positions. These positions are meant to cause increased pressure in the pathways of the flexor hallucis longus and illicit the type of pain response associated with dancer’s tendinitis. This tenderness coupled with a reduced range of motion may be all an examiner needs to accurately deduce flexor hallucis longus injury.

If flexor hallucis injury is suspected, the diagnosing may be escalated to the imaging room where an ultrasound and MRI can provide further insight and more a more accurate assessment of the damage around the flexor hallucis longus.

Conventional Treatments of Flexor Hallucis Longus Pain

Pain in the flexor hallucis longus and the associated tendon can be managed or treated in several ways. While most of the following treatments cannot completely eradicate the pain, they can help achieve some measure of comfort for those suffering from it. Please note that this is not an extensive list of the treatment options available, just the most popular treatment methods which doctors suggest.


Perhaps the most common of the treatments on this list, exercise helps to alleviate pressure around the flexor hallucis longus and strengthen the supporting muscles around it. Often times, the exercises which are prescribed are part of a progressing training regimen designed to guide the patient through a number of levels based on their stage in the recovery process. This progression is usually based on the amount of load that the flexor hallucis longus can tolerate without inducing the pain being treated.

Most of the exercises used in flexor hallucis longus treatment involve periodically flexing and relaxing the injured muscle. Typical exercises include:

  • Resisted plantarflexion of the big toe
    • An elastic band is looped around the big toe and gets tugged towards the patient to induce a flexed state in the flexor hallucis longus.
  • Marble pickups
    • A patient uses their fourth and big toes to pick a small object off the floor and drop it into a nearby receptacle.
  • Towel scrunches
    • A towel is laid flat on the floor and the patient uses their big and fourth toes to “scrunch” it up while lifting their heel off the floor.
  • Tip toe
    • A patient will plant a single foot on the floor and raise the other leg up while shifting their weight between the base of the big toe and the heel. The patient may be asked to flex their big toe in addition to this exercise.

Activity Modification and Load Management

Along with exercise, activity modification can be of great importance to those suffering from flexor hallucis longus pain. By guiding patients into new habits, physical therapists can help patients reduce the load which falls on the injured muscle tissue and understand the limitations of which their injury causes. These sessions should help patients reach the edge of their limitation without over-exerting their injury. If a patient experiences a flare up due to one of these sessions, they should relay this information to their therapist in order to reorganize their training.

Massage and Stretching

Another popular group of tactics for alleviating immediate pain in the flexor hallucis longus are periodic massages and stretches. These tactics aim to extend and soften the injured muscle thereby decreasing the tension placed on it.

Stretches will typically be done under the supervision of a trained professional as they can cause flare ups if done improperly. If the emphasis of the stretch is placed on the back of the ankle, for example, the flexor hallucis longus tendon may become pinched and irritated.

Massages can be done at home, without supervision by using a foam roller, trigger ball, or other similar massage tool under the foot, at the back of the ankle or on the calve. These simple tools can provide immediate relief at the onset of a flare up and may alleviate pain completely for a small period of time.

Medication and Pharmaceuticals

If the pain is persistent and robust, a doctor may prescribe medication or recommend over-the-counter anti-inflammatory medication. These medications can be used in conjunction with physical therapy or on their own to provide pain relief and reduce inflammation locally. While these treatments can be an effective tool to help guide recovery, they do run the risk of addiction or even further degeneration of the tissue over prolonged use. In order to properly medicate, a consultation from a medical expert is necessary before beginning a medication routine.

Splinting and Load Bearing Assistance

Splinting and the use of load bearing devices such as canes are not typically required for flexor hallucis longus pain but can occasionally be recommended if the injury is severe enough. These devices help manage the physiology of movement around the flexor hallucis longus as well as decrease the load the injured muscle must bear.


Surgery is reserved as a last resort in the treatment of flexor hallucis longus pain. Failure of conservative treatment options means that doctors will often recommend highly invasive surgery which could entail long recovery periods, opioid prescriptions, and assisted rehabilitation before returning the muscle to function. Even so, the flexor hallucis longus may never return to full function and may require a permanent routine of the above treatment methods post-surgery.

Regenerative Medicine and Flexor Hallucis Longus Pain

Although the above stated conventional treatment methods may be enough to alleviate the pain caused by flexor hallucis longus injury, regenerative medicine can help boost the body’s response to these treatments as well as provide longer lasting relief from the pain.

A relatively new treatment option, regenerative medicine uses cells derived from a patient’s blood, fat, and bone marrow to provide the body with a new line of defense against degenerative illnesses. By isolating portions of these cells and processing them, doctors have created a new medicine which helps to regenerate damaged tissue as well as accelerate the body’s natural healing functions.

At CELLAXYS we specialize in two of these forms of regenerative medicine – Platelet Rich Plasma Therapy, or PRP, and Stem Cell Therapy.

Using the first of these options, PRP, doctors first extract and isolate the platelets found in blood then reinject them into the sight of injury. Platelets naturally heal the body by binding to the damaged portions of a tissue and then signaling the body to attract healing factors to their location. By amplifying the body’s response to injury, this form of therapy has been shown to be an effective treatment for degenerative illnesses such as tendinitis, post-surgical trauma, arthritis, and other tissue deficient syndromes.

Stem Cell Therapy works much the same way as PRP. By extracting fat and bone marrow then processing these cells, doctors have been able to create cells which are able to regenerate lost tissues. Known formally as mesenchymal stem cell therapy, this relatively new medicine works by calling on the body’s healing factors and providing a suitable environment for these factors to work. After injection into the site of degeneration, mesenchymal stem cells form a shelter around the tissue and chemically signal the body to send platelets and other building blocks to restore the damaged muscle, cartilage, and tendon.

By using Regenerative Medicine alongside conventional forms of therapy, the recovery period for flexor hallucis longus injury can be cut substantially. Additionally, by using regenerative medicine, relief from the pains caused by muscle and tendon damage can be extended over a much longer period of time than conventional treatments, typically lasting anywhere from six months to a year. These medicines may even be enough to prevent the application of invasive surgery if the issues are caught early enough.


Flexor hallucis longus pain can seriously impede the daily routine of those who suffer from it. While conventional methods may be enough to manage the pain, they require a large amount of effort over an extended period of time and may not return the damaged tissue to its normal function.

Regenerative medicine is making leaps and bounds in the treatment of this and other degenerative ailments and may soon become a more popular alternative to ineffective conventional treatments.

To discuss if regenerative medicine is right for your specific case, consult one of our trained medical experts at CELLAXYS today.

Dr. Matthew HC Otten

Dr. Matthew HC Otten

Director of Orthopedic & Orthobiologics
Fellowship-trained & Board Certified in Sports medicine
Director Angiography at Harvard Clinical Research Institute
Michigan Stage University Alumni