Burning in the Sole of Your Foot: When the Problem Is a Nerve, Not the Fascia

What this video covers

• What tarsal tunnel syndrome is, and why a squeezed posterior tibial nerve at the ankle causes pain in the sole
• How to tell tarsal tunnel syndrome apart from S1 lumbar radiculopathy, diabetic polyneuropathy, plantar fasciitis, and Morton neuroma
• What nerve conduction studies, ultrasound, and a diagnostic nerve block can and cannot tell you
• How hydrodissection is done, and why the only blinded controlled trial is in the wrist, not the foot
• When peripheral nerve stimulation is considered, and why its evidence is graded very low to low
• The real risks, and how long the benefit really lasts
• MEDICAL DISCLAIMER: This content is for educational purposes only and is not medical advice. It does not substitute for professional diagnosis or treatment. Always consult a licensed healthcare provider regarding your condition. Viewing this video does not establish a doctor-patient relationship.

Burning across the sole of the foot that builds as you stand through the day can come from tarsal tunnel syndrome. That is a squeezed posterior tibial nerve behind the inner ankle bone. The heel often feels normal. That sets it apart from plantar fasciitis, where the heel hurts most in the first steps out of bed.

It is two in the morning. You have been off your feet for hours, and the sole of your foot is on fire. Not sore. Burning, like a hot electric band running from the inside of your ankle into the arch and the toes. It builds through the day, and at night it wakes you. You were told it is plantar fasciitis. You had the heel injections, the night splint, the new shoes. None of it lasted.

This article explains why that pattern often points away from the plantar fascia. It covers what the tarsal tunnel is. It shows how a squeezed nerve at the inner ankle makes exactly the symptom you feel. And it shows how the diagnosis is really sorted out before anyone reaches for a needle.

What is the tarsal tunnel, and what causes tarsal tunnel syndrome?

Behind the bump on the inside of your ankle is a tunnel. Its floor is bone. First comes the medial malleolus of the tibia (the inner ankle bump) above, then the inner wall of the talus, then the calcaneus (the heel bone). Its roof is the flexor retinaculum, a tough band of tissue. Running through that space are three flexor tendons, the posterior tibial artery and its paired veins, and the posterior tibial nerve.

Past the tunnel, that nerve splits into the medial and lateral plantar nerves. These supply the sole of the foot. The medial calcaneal branches serve the heel pad. They usually leave above the retinaculum. That detail matters more than it sounds, and we will come back to it.

Tarsal tunnel syndrome is a squeezed posterior tibial nerve inside that fibro-osseous space (a space walled by bone and tough tissue). The tunnel has bone on one side and a rigid band on the other, so it cannot get bigger. Anything that fills it raises the pressure inside:

• Tenosynovitis: inflammation and swelling of the tendon sheaths that pass through the tunnel
• Varicose veins in the tunnel
• A ganglion cyst, often growing from the subtalar joint
• Hindfoot valgus: the heel drifts outward and keeps the retinaculum pulled tight all the time
• Post-traumatic scarring after an ankle injury or surgery

The next step in the story is where honesty matters. Raised pressure is thought to choke blood flow in the epineurium, the nerve’s own blood-supplied sheath. That leads to fluid buildup inside the nerve and patchy loss of myelin (the nerve’s insulation). Signals slow down. With pressure that keeps going, axons (the nerve’s wires) are lost. That chain is shown mainly in animal compression models, not shown inside human tarsal tunnels. It is a plausible explanation, not a measured fact in patients. Treat it as a mechanism, not proof.

Why does tarsal tunnel burning get worse through the day and wake you at night?

Two features of this condition line up with the anatomy.

The heel is often the part that feels normal. The medial calcaneal branches usually peel off before the retinaculum, so they escape the squeeze. That is why the burning spreads across the arch, the ball of the foot and the toes. Meanwhile the heel, the exact place plantar fasciitis hurts, can feel normal. Plantar fasciitis classically hurts at the heel. It is worst in the first few steps out of bed, then eases as you move. A burn across the whole sole that gets worse the longer you stand is a different pattern.

Standing loads the tunnel. Standing raises pressure in the space. So the pain piles up through a work day instead of fading with use. At night, blood pooling in the veins of the tunnel is thought to keep the nerve irritated after you lie down. That is why people describe the worst of it in the small hours.

One warning about that night pain, because people often read too much into it: night pain is not a signature of tarsal tunnel syndrome. Diabetic polyneuropathy is at its worst at night too, and it is far more common. Night pain tells you the problem is in a nerve. It does not tell you where the problem is.

What can be mistaken for tarsal tunnel syndrome?

Repeat heel injections are not new evidence. When a third one fails, it is usually the same missed diagnosis, repeated, not a treatment that fell short. Care aimed at the fascia (injections, night splints, supportive shoes) does what it is built to do for a fascia problem. It is just not aimed at a nerve.

Several conditions cause burning foot pain. They overlap, and each needs different treatment:

• S1 lumbar radiculopathy burns down the calf and into the sole. But the problem is at the spine, not the ankle.
• Diabetic (or other metabolic) polyneuropathy burns in both feet, the same on each side, in a stocking pattern.
• Morton neuroma sits between the long bones at the front of the foot, near the toes (the metatarsal heads).
• Plantar fasciitis centers on the heel. It is worst with the first steps of the day.
• Complex regional pain syndrome adds color and temperature change, swelling, and pain from light touch.

These can also exist together. A nerve already stressed by metabolic disease may handle pressure poorly. So a polyneuropathy does not rule out a trapped nerve sitting on top of it. That “double crush” idea, though, is more plausible than proven. It is a reason to keep an open mind, not a reason for a needle.

The other thing often missed is the order of steps. A metabolic neuropathy that nobody has diagnosed is not fixed by an injection at your ankle.

How is tarsal tunnel syndrome diagnosed?

Bloodwork comes before imaging

The first orders here are lab tests, not scans. We check fasting glucose and hemoglobin A1c. We check vitamin B12, with methylmalonic acid if the B12 is borderline. We check thyroid function. When the history calls for it, we add kidney function and an honest count of alcohol intake. Body-wide causes get ruled out, or found and treated, before anyone talks about a procedure.

Examination, then electrodiagnostics

In the exam room, the question is whether tapping behind the medial malleolus brings back your exact pain. We also check whether any numb area follows a plantar nerve, a nerve root, or neither. That tapping sign shows up in people with no trapped nerve at all, and in widespread neuropathy. It opens the case. It does not close it.

Then come nerve conduction studies. Patel and colleagues wrote an evidence-based review for the American Association of Neuromuscular & Electrodiagnostic Medicine. It was published in Muscle Nerve in 2005. They screened the studies on suspected tarsal tunnel syndrome. They concluded that nerve conduction studies may be useful for confirming tibial neuropathy at the ankle — at recommendation Level C. That is the weakest useful grade. They also found that sensitivity and specificity could not be worked out from the studies available.¹

What that means in practice is one of the most important lines in this article: a normal nerve conduction study does not exclude tarsal tunnel syndrome. If you were told a normal study closed the question, that is a common misreading of what a Level C recommendation supports.

Imaging answers different questions

• Ultrasound shows what nerve testing cannot: a cyst, a swollen tendon sheath, varicose veins, a nerve swollen just above a narrow spot. It shows them live, with the ankle moving. It depends on the skill of the person scanning. It has no proven sensitivity for this condition.
• MRI is better when the question is a mass, bone marrow, or dense scar.
• Weight-bearing radiographs show how the back of the foot lines up, which ultrasound cannot judge.

The diagnostic nerve block

A diagnostic tibial nerve block helps find where the pain comes from. It is not a proven test that confirms the diagnosis. There is no agreed level of relief that proves it. And an uncontrolled block (one with no comparison) carries a real false-positive rate. It is one clue among several. It is not a verdict.

How is tarsal tunnel syndrome treated, and what does the evidence support?

Treatment starts only when history, exam, imaging and block all point to the same nerve in the same tunnel. It also starts only after orthotics, activity changes and a real course of physical therapy have failed. None of what follows belongs at a first visit. None of it belongs at all in a foot that has not been worked up. Undiagnosed foot pain, or a possible fracture or infection, is a reason to stop and finish the diagnosis. It is not a reason to inject. The wider range of non-surgical foot problems that get checked first is laid out on the foot pain treatment page.

First decision: is there something in the tunnel to remove?

Sometimes ultrasound or MRI shows something filling the tunnel: a ganglion, a mass, large varicose veins, dense scar. Then the definitive treatment is surgical excision and decompression, not an injection. The right step is a referral to a surgeon. Injection care is for a tunnel that is tight with nothing to remove, or for a person who cannot have surgery. Anyone offering a needle before that question is answered has skipped the question that matters.

Hydrodissection

Hydrodissection is the first procedure step. A high-frequency linear ultrasound probe finds the nerve in cross-view, sitting against the artery and veins. The needle moves in along the ultrasound beam, in full view the whole time. Fluid is placed between the nerve and whatever is squeezing it. The details of the procedure, such as what fluid is used and how ultrasound and fluoroscopy (live X-ray) work together, are covered on the hydrodissection page.

Here is where the evidence has to be stated plainly:

• The proposed mechanism is freeing scar bands around the nerve and diluting the chemicals that drive inflammation. That idea is inferred from cadaveric and animal work, not shown in living humans.
• The strongest controlled evidence is not in the foot. Wu and colleagues, in Muscle Nerve in 2019, randomized 34 patients with mild-to-moderate carpal tunnel syndrome(the wrist, the median nerve). Each was assigned by chance to either perineural saline hydrodissection (saline around the nerve) or a control subcutaneous injection (a shot under the skin), double-blind. Symptom scores pulled ahead of control only at the second and third post-treatment months. Nerve cross-sectional area was smaller at every check through six months. But the symptom advantage was no longer present at six months.²
• In the tarsal tunnel itself, published experience is case series. There is no controlled trial. It rests on indirect evidence.
• The injected fluid is saline, 5% dextrose, or corticosteroid.

When there is benefit, it is measured in months, not forever. Individual results vary.

The risks you should hear before consenting

The posterior tibial nerve lies right against the posterior tibial artery and vein, inside a space that cannot expand. That layout drives the risk list:

• Bleeding, injection into a blood vessel, and a hematoma (a pocket of blood) inside a closed tunnel
• Infection
• Injury inside the nerve, causing new or worse burning, numbness, or weakness
• Several hours of a numb sole from the local anesthetic. do not drive until sensation returns. Move carefully on a foot you cannot feel, and protect it from heat and pressure. A foot that is numb for a while carries both a fall risk and a burn risk. Both matter most if you have diabetes or neuropathy
• If corticosteroid is used, a temporary rise in blood sugar lasts several days. Flushing and poor sleep are possible. With repeated injections, the local tissue may thin

If you take a blood thinner, a diabetes drug, or anything else that could be affected, bring it up before the procedure. Do not start, stop, or change any medication without consulting your physician.

Peripheral nerve stimulation is last-line

Peripheral nerve stimulation is not a foot treatment. It is saved for nerve pain that is confirmed, has not responded to treatment, and is pinned to one spot, after image-guided care has failed. A systematic review by Char and colleagues in Biomedicines in 2022 graded the evidence for implantable peripheral nerve stimulation in peripheral neuropathic pain (pain from damaged nerves outside the brain and spine) as very low to low quality. No study in it looked at tarsal tunnel syndrome or a trapped tibial nerve.³ Risks of the device include the wire moving or breaking, skin wearing through, infection that can force removal of the device, loss of coverage, and limits on MRI.

A composite picture of how this unfolds

What follows is a composite. It is a picture built from many patients with this condition, not one person’s chart. All of it is what we see in practice, not a trial result. It is one plausible course, not a typical or promised one.

An adult on their feet all day. Two years of burning in the sole, worse by evening, waking them before dawn. Three heel injections, orthotics, and physical therapy aimed at the fascia. A normal nerve conduction study, which they were told closed the question. Tapping behind the inner ankle bone brought back the exact pain. That was a hint, not a final answer. The numb area followed a plantar nerve, not a nerve root. Ultrasound showed a swollen tendon sheath narrowing the tunnel, and no mass that needed removal. A diagnostic block dropped the burning for the duration of the anesthetic. That supported the diagnosis but did not prove it.

Hydrodissection changed almost nothing in the first weeks. They were told ahead of time to expect that. The shift came slowly. It was clearer by the second month and clearer again by the third. That is the same window in which the wrist trial pulled ahead of its control. Not instant, and not complete. The first orthotic failed and had to be remade. Near five months the burning began to return. A second hydrodissection was done. It was said up front that this is control measured in months. Individual results vary.

Frequently asked questions

Key takeaways

• Tarsal tunnel syndrome is a squeezed posterior tibial nerve in a tunnel of bone and tough tissue at the inside of the ankle. The heel branches usually leave above the tunnel. So the sole burns while the heel can feel normal. That is the opposite of the plantar fasciitis pattern.
• The pressure chain taught in textbooks comes mainly from animal models. Night pain points to a nerve but not to a place. So the diagnosis rests on ruling other causes in or out, not on the symptom alone.
• A normal nerve conduction study does not rule out the diagnosis. The evidence for nerve testing here is only Level C. A diagnostic block points to the spot but does not confirm it.
• Hydrodissection in the tarsal tunnel is backed by case series plus one blinded 34-patient trial in the wrist. There, symptom scores pulled ahead of control only at the second and third months, and no longer did so at six. Peripheral nerve stimulation rests on very-low-to-low-quality evidence, with no tarsal tunnel studies at all.
• If burning in your sole has outlasted every treatment aimed at your heel, ask which nerve is being treated. And ask to see it on the ultrasound screen before anything goes into your foot.

This article is educational and is not a substitute for evaluation, diagnosis, or treatment by a physician. Individual results vary. Do not start, stop, or change any medication without consulting your physician. To be evaluated, call (314) 481-5000 or text (314) 886-5902, or request an appointment at painmd.tv/appointment.

References

1. Patel AT, et al. Usefulness of electrodiagnostic techniques in the evaluation of suspected tarsal tunnel syndrome: an evidence-based review. Muscle Nerve. 2005. PMID 16003732. PubMed
2. Wu YT, et al. Nerve hydrodissection for carpal tunnel syndrome: a prospective, randomized, double-blind, controlled trial. Muscle Nerve. 2019. PMID 30339737. PubMed
3. Char S, et al. Implantable peripheral nerve stimulation for peripheral neuropathic pain: a systematic review of prospective studies. Biomedicines. 2022. PMID 36289867. PubMed

Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP — Board Certified in Anesthesiology, Pain Medicine, Interventional Pain Management, Addiction Medicine, and Obesity Medicine. Last reviewed July 2026.

Dr. Gurpreet Singh Padda, MD, MBA, MHP