Signs the Flexor Digitorum Brevis is causing your heel pain
You wake up, swing your legs to the edge of the bed, and…hesitate.
You know this is going to hurt.
The good foot moves to the ground first – you learned from that mistake over a month ago. You brace and put down the other foot, the ungrateful one that will not get better despite the trip to the podiatrist, the injection, physical therapy, the shoe inserts, the ice bottle massage, and the stretching exercises.
The foot touches down.
It’s not so bad, you think ‘those stretches and night sock are helping!’
Then you step and the sharp pain feels as if the tissue from the back of the heel is ripping apart.
You think to yourself, this plantar fasciitis won’t go away, as you force your leg forward and take the next step and the next as the pain slowly reduces.
Misdiagnosing heel pain
A poorly constructed diagnosis from a practitioner or WebMD is a common in medicine. We go more into diagnosis in this article. For plantar heel pain, the most common misdiagnosis happens with differentiating plantar fascia from the flexor digitorum brevis., but there are numerous other structures that can cause pain, including: fat pad, heel bone injuries(this includes calcaneal stress fractures, bone spurs, and bony stress syndromes), the plantar muscle intrinsics (flexor digitorum brevis, abductor hallucis, and abductor digiti minimi), and nerves (lateral plantar nerve and tibial nerve at the tarsal tunnel).
In order to treat heel pain effectively, you must know the pain generator. Otherwise, the treatment plan is guesswork.
First day in our clinic
When someone walks in for their first physical therapy session, landing with the foot flat and shortened steps due to pain, they wonder what we can do for plantar fasciitis. The diagnosis is clear in their minds.
The patient tried everything:
- Rolling a frozen water bottle on the bottom of the foot
- Toe stretch
- Calf stretching exercises
- Massage to the calf muscle
- Towel Stretch
- Marble Pickups (my least favorite exercise)
- Supportive new shoes then soft shoes then shoe inserts
- Strassberg sock or a night splint (or both)
- Corticosteroid Injections
- Occasionally surgery on the plantar fascia (hopefully we catch them before this)
With heel pain, we see an escalation of treatment. Some of these activities reduce pain for a little while before returning.
The water bottle drops the pain from numbing the area, but the pain is back when the numb feeling is gone.
The sock makes the first few steps a little less terrible. The stretches give relief that does not last.
Overall, the symptoms seem to progress and become more and more debilitating.
Diagnosing plantar fasciitis when you have a flexor digitorum brevis tendinopathy
As a general rule, you will be diagnosed with plantar fasciitis if you have heel pain. I have not seen a patient reporting heel pain that was diagnosed with anything other than plantar fasciitis for the last 5 years.
This is not the only structure on the bottom of the foot that can cause pain. Plantar fasciitis is not a common diagnosis in our clinic.
You pain can be caused by any one or combination of the following:
- Flexor Digitorum Brevis
- Abductor Hallucis
- Abductor Digiti Minimi
- Fat Pad Trauma or Atrophy
- Stress fracture
- Lateral Plantar Nerve
- Medial Plantar Nerve
- Tarsal Tunnel Syndrome
- Low back referral
- Hip joint referral
- Plantar Fascia
- Surgical Scars
If you tried the treatments above and your heel pain is still there, maybe you don’t have plantar fasciitis. The flexor digitorum brevis is most likely the culprit.
Signs the flexor digitorum muscle is causing your heel pain
What starts to clue you in that the pain is not plantar fasciitis but instead the flexor digitorum brevis or one of the other plantar foot muscles?
Cramping on the bottom of the foot
The plantar fascia is not a muscle and should not cramp. If your foot cramps and causes the pain, then it is highly unlikely that your plantar fascia is the problem. This is an important thing to catch in the medical history or subjective with the patient. Often times, you may think its not cramping. Instead it feels like the toes get stuck in a curled position.
The plantar muscle cramping is most common your ankle joint is plantar flexed and then the toes are flexed. With exercises, the most common one that causes the foot cramping is the rearfoot elevated splits squats. The cramping foot placed on the bench will typically make the exercise unbearable.
If you sleep on your back at night, you may also get cramping from this position, especially with heavier blankets.
Other common activities include quad stretching if you hold onto the foot for the stretch, toe pointing in ballet, or sitting on your foot.
Pain with resisted toe flexion
This is similar to the first sign. If you can induce the heel pain or a cramp with resisted toe flexion, the flexor digitorum brevis is most likely the pain generator.
The initial physical exam can be negative for this finding, meaning there is no pain but after a cramp or loading with walking, resisted toe flexion becomes painful.
We also find that after several repititions of the exam, a sore heel can develop while there is still no pain with the test.
I believe part of the issue with this is that the flexor digitorum brevis is used by the body as a local foot and ankle stabilizer, not a toe flexor, so resisted toe flexion does not provide enough load to the muscle to cause pain. The takeaway here is that you need to monitor pain after trying the resisted test and you may need to do it multiple times.
Increased pain at midstance and initial heel rise
The flexor digitorum brevis supports the medial longitudinal arch of the foot. The muscle engages when your foot is flat on the ground. The plantar fascia is not loaded until preswing. You actually have more than a doubling in tension across the plantar fascia at preswing compared to midstance and terminal stance.
The plantar fascia gets the most tension during preswing. This is due to a unique property of the fascia called the windlass mechanism. When the toe is dorsiflexed, the plantar fascia is pulled tight, and pulled tight across the metatarsal heads.
A direct application of this means a shoe with a carbon plate would reduce the pain associated with plantar fasciitis but have no impact on a flexor digitorum brevis injury (the harder surface may actually irritate the flexor digitorum brevis).
Flexor Digitorum Brevis Test
The flexor digitorum brevis and the plantar fascia have attachments by each on the calcaneus (the heel bone. They also run the same course on the foot from the heel to the toes.
A quick way to differentiate the two is to do the Flexor Digitorum Test.
Step 1. Tension the plantar fascia by dorsiflexing the toes
Step 2. Palpate the plantar fascia, especially the area that normally hurts
Step 3. Take the tension off the plantar fascia by plantarflexing the toes
Step 4. Palpate the same locations
If the pain is increased with the toes plantar flexed, your heel pain is coming from the flexor digitorum brevis.
The presence of morning pain does not differentiate between plantar fasciitis and a plantar muscle tendinopathy. Both injuries commonly have this report. With tissue that has chronic inflammation, more stiffness and discomfort is common after a period of rest.
Pain worse with initial loading
This is another one that does not differentiate between plantar fasciitis and the muscle. A common report is that walking or running feel terrible but then gets better.
Pain post exercise
A more common report is an increase in muscle cramping or tension post exercise. This is another significant factor points towards a dysfunctional motor response in the flexor digitorum brevis. When a patient has a negative physical exam during our physical therapy session, I will often have them go do the activity and then retest. Now the resisted toe flexion is positive and its easier to cramp the muscles.
Holes in your foot bed
If you pull out the foot bed from your shoes, you may notice indentations where your toes normally push down. If the indentations are deep (sometimes there is actually a hole in the foot bed where the big toe push down) then you are likely burying your toes during the day and with walking.
When you bury your toes, its often a sign of weakness in your plantar flexor muscles or an issue with balance or both. The problem is that this overloads and irritates the flexor digitorum brevis over time.
You may notice blisters on the end of the toes. This can be the same process happening as well.
Abnormal walking style (gait)
Since midstance is painful, we will see that stride length is shortened to reduce time on the painful foot. For a painful plantar fasica, we see a similar shortening but the change happens by avoiding heel rise in terminal stance.
This is a subtle difference that your medical professional can catch.
Concurrent orthopedic diagnoses
When you initially develop heel pain, it may be your only issue. Unfortunately, this pain tends to change your loading pattern (as mentioned above) so other problems can arise. The most common are posterior tibiailis and achilles tendinopathy.
The achilles tendon and calf muscles are a critical component of normal walking. However the heel pain location is not the same. It is on the back of the heel, not the bottom.
Posterior Tibialis Tendinopathy
When the posterior tibialis is injured, the distal insertion is into the arch of the foot. Careful palpation can determine if this tendon is also causing pain in the arch of the foot.
Getting it stronger will actually unload the planter muscles.
There are three diagnoses that need to be mentioned, stress fracture, neuropathy, and fat pad injury that must be ruled out.
For stress fracture, we look for heel swelling about the medial and lateral ankle. We also do a calcaneal squeeze test. If these are positive, the heel must be unloaded for a minimum of 5 days prior to a controlled return to activity program.
If you have a stress fracture, it normally heals quickly with unloading but it must be complete unloading. Walking will still overload the healing bone. Most pain is reported during heel strike of initial contact.
Nerve damage or irritation is more common if the abductor hallucis is involved. This is called a tarsal tunnel syndrome with the tibial nerve is involved at the location of the medial ankle. The plantar nerves get into the bottom of the foot by passing through the tarsal tunnel and deep to the abductor hallucis. So if the abductor hallucis becomes overactive and painful, it can compress the nerves, leading to reports of numbness and tingling.
If you have numbness or tingling, then there is nerve involvement. This does not mean that there is irreversible nerve damage, just that it needs to be addressed in your plan of care.
The longer you have heel pain, the more likely a nerve is to get involved. For recalcitrant heel pain that has been lingering for over a 3 month period, a nerve is likely involved.
The fat pad, sometimes referred to as a heel pad, is a specialized structure on the bottom of calcaneus. When damaged, it is exquisitely tender. As a physical therapist, the most important step is unloading in a similar fashion to the stress fracture.
A heel cup or heel protector can be used with walking to determine if the heel pain is from fat pad atrophy.
Conclusion – Flexor Digitorum Brevis vs Plantar Fasciitis
The first step in treating heel pain is understanding the pain generator. The most commonly used criteria to diagnose plantar fasciitis does not differentiate between between the flexor digitorum brevis and the plantar fascia.
If you have one or more of the signs, or have been trying the normal suggestions for treatment without improvement, then the flexor digitorum brevis might be the culprit. If that is the case, then there are other things to consider.
Reach out if you have questions
If you are struggling with heel pain, let us know. You can schedule a visit with one of our physical therapists today.
- Chen Y-N, Chang C-W, Li C-T, Chang C-H, Lin C-F. Finite Element Analysis of Plantar Fascia During Walking: A Quasi-static Simulation. Foot & Ankle International. Published online September 4, 2014. doi:10.1177/1071100714549189