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 compression of the 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 ultrasound-guided hydrodissection is performed, 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 material risks, the off-label status, and the realistic duration of benefit
• 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.

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 have been told it is plantar fasciitis. You have had the heel injections, the night splint, the new shoes. None of it lasted.

This article explains why that pattern often points somewhere other than the plantar fascia, what the tarsal tunnel is, how a compressed nerve at the medial ankle produces exactly the symptom you feel, and how the diagnosis is actually sorted out before anyone reaches for a needle.

The tarsal tunnel: a compartment that cannot expand

Behind the bump on the inside of your ankle is a tunnel. Its floor is bone — the medial malleolus of the tibia above, then the medial wall of the talus, then the calcaneus (the heel bone). Its roof is the flexor retinaculum, a tough fibrous band. 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 divides into the medial and lateral plantar nerves, which supply the sole of the foot. The medial calcaneal branches — the ones that serve the heel pad — usually leave above the retinaculum. That anatomical detail matters more than it sounds, and we will come back to it.

Tarsal tunnel syndrome is compression of the posterior tibial nerve inside that fibro-osseous space. Because the tunnel has bone on one side and a rigid band on the other, it cannot enlarge. Anything that fills it raises the pressure inside it:

• Tenosynovitis — inflammation and swelling of the tendon sheaths passing through the tunnel
• Varicose veins in the tunnel
• A ganglion cyst, often arising from the subtalar joint
• Hindfoot valgus, where the heel drifts outward and keeps the retinaculum under constant tension
• Post-traumatic scarring after an ankle injury or surgery

The next step in the story is where honesty matters. Raised pressure is thought to throttle blood flow in the epineurium — the nerve’s own vascular sheath — producing fluid accumulation inside the nerve, focal loss of myelin, slowed conduction, and, with sustained compression, loss of axons. That cascade is established chiefly in animal compression models, not demonstrated inside human tarsal tunnels. It is a plausible explanation, not a measured fact in patients. Treat it as mechanism, not proof.

Why the burning builds through the day and wakes you at night

Two features of this condition line up with the anatomy.

The heel is often the part that feels normal. Because the medial calcaneal branches typically peel off before the retinaculum, they escape the compression. So the burning spreads across the arch, the ball of the foot and the toes while the heel — the exact place plantar fasciitis hurts — can feel unremarkable. Plantar fasciitis classically hurts at the heel and 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 entirely.

Standing loads the tunnel. Weight-bearing raises pressure in the compartment, so the pain accumulates through a working day rather than fading with use. At night, venous congestion in the tunnel is thought to keep the nerve irritated after you lie down — which is why people describe the worst of it in the small hours.

One caution about that night pain, because it is frequently over-read: 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 neural. It does not tell you where the problem is.

What the plantar fasciitis label misses

Repeat heel injections are not new evidence. When a third one fails, that is usually the same missing diagnosis being repeated rather than a treatment that underperformed. Symptom-directed care for the fascia — injections, night splints, supportive shoes — does what it is designed to do for a fascial problem. It simply is not aimed at a nerve.

Several conditions produce burning foot pain, they overlap, and they require 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, symmetrically, in a stocking distribution.
• Morton neuroma sits between the metatarsal heads in the forefoot.
• Plantar fasciitis centers on the heel, worst with the first steps of the day.
• Complex regional pain syndrome adds color and temperature change, swelling, and pain from light touch.

These also coexist. A nerve already stressed by metabolic disease may tolerate compression poorly, so a polyneuropathy does not rule out an entrapment sitting on top of it. That “double crush” idea, however, has more plausibility than proof — it is a reason to stay open-minded, not a justification for a needle.

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

What a real evaluation looks like

Bloodwork comes before imaging

The first orders here are laboratory, not radiological: fasting glucose and hemoglobin A1c, vitamin B12 with methylmalonic acid if the B12 is borderline, and thyroid function. Where the history warrants it, kidney function and an honest accounting of alcohol intake. Systemic causes get excluded — or found and treated — before anyone discusses a procedure.

Examination, then electrodiagnostics

In the room, the question is whether percussion behind the medial malleolus reproduces your exact pain, and whether any sensory deficit follows a plantar nerve, a nerve root, or neither. That percussion sign turns up in people with no entrapment at all, and in generalized neuropathy. It opens the argument. It does not close it.

Then nerve conduction studies. An evidence-based review by Patel and colleagues for the American Association of Neuromuscular & Electrodiagnostic Medicine, published in Muscle Nerve in 2005, screened the literature on suspected tarsal tunnel syndrome and concluded that nerve conduction studies may be useful for confirming tibial neuropathy at the ankle — at recommendation Level C, the weakest useful grade — and that sensitivity and specificity could not be determined from the available studies.¹

The practical consequence is one of the most important sentences 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 misunderstanding of what a Level C recommendation supports.

Imaging answers different questions

• Ultrasound shows what electrodiagnostics cannot: a cyst, a distended tendon sheath, varicosities, a nerve swollen just above a narrowing — live, with the ankle moving. It is operator-dependent, and it has no established sensitivity for this condition.
• MRI answers better when the question is a mass, bone marrow, or dense scar.
• Weight-bearing radiographs answer hindfoot alignment, which ultrasound cannot assess.

The diagnostic nerve block

A diagnostic tibial nerve block helps localize the pain generator. It is not a validated confirmatory test: there is no accepted response threshold that proves the diagnosis, and an uncontrolled block carries a real false-positive rate. It is one input among several. It is not a verdict.

What treatment involves, and what the evidence actually supports

Treatment begins only when history, examination, imaging and block converge on the same nerve in the same tunnel — and only after orthotics, activity modification and a genuine course of physical therapy have failed. None of what follows belongs at a first visit, and none of it belongs at all in a foot that has not been worked up: undiagnosed foot pain, or a suspected fracture or infection, is a reason to stop and finish the diagnosis, not a reason to inject. The wider range of non-surgical foot problems that get evaluated first is set out on the foot pain treatment page.

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

If ultrasound or MRI shows something occupying the tunnel — a ganglion, a mass, gross varicosities, dense scar — the definitive treatment is surgical excision and decompression, not an injection, and the correct step is a surgical referral. Injection-based care is for the tunnel that is tight with no lesion to remove, or for the person who cannot undergo surgery. Anyone offering a needle before that question is answered has skipped the question that matters.

Ultrasound-guided hydrodissection

Hydrodissection is the first interventional step. Using a high-frequency linear transducer, the nerve is identified in short axis, sitting against the artery and veins. The needle is advanced in-plane under continuous ultrasound vision, and fluid is delivered between the nerve and the structure compressing it. The mechanics of the procedure — what fluid is used, and why ultrasound rather than x-ray — are covered on the ultrasound-guided hydrodissection page.

Here is where the evidence has to be stated plainly:

• The proposed mechanism — separating perineural adhesions and diluting inflammatory mediators — is inferred from cadaveric and animal work, not demonstrated 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 — to perineural saline hydrodissection or a control subcutaneous injection, double-blind. Symptom scores separated from control only at the second and third post-treatment months; nerve cross-sectional area was smaller at all timepoints 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. This is best understood as an investigational application supported by indirect evidence.
• The procedure is off-label whatever the injectate — saline, 5% dextrose, or corticosteroid. No injectate is FDA-approved for perineural hydrodissection at the ankle. Know that before you consent.

Benefit, where it occurs, is measured in months rather than permanence. Individual results vary.

The risks you should hear before consenting

The posterior tibial nerve lies directly against the posterior tibial artery and vein, inside a compartment that cannot expand. That geometry drives the risk list:

• Bleeding, injection into a blood vessel, and hematoma inside a closed tunnel
• Infection
• Intraneural injury producing new or worsened 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 temporarily insensate foot carries both a fall risk and a burn risk, and both matter most if you have diabetes or neuropathy
• If corticosteroid is used, a temporary rise in blood sugar for several days, along with possible flushing and disturbed sleep, and, with repeated injections, possible local tissue thinning

If you take a blood thinner, a diabetes medication, or anything else that could be affected, that belongs in the pre-procedure conversation. 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 reserved for confirmed, refractory, well-localized neuropathic pain 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 as very low to low quality, and no included study addressed tarsal tunnel syndrome or tibial nerve entrapment.³ Device-specific risks include lead migration or fracture, skin erosion, infection that can force removal of the device, loss of coverage, and MRI restrictions.

A composite picture of how this unfolds

What follows is a composite — a picture assembled from many patients with this condition, not one person’s chart. Everything in it is practice observation, not a trial result, and it is one plausible course rather than 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. Percussion behind the inner ankle bone reproduced the exact pain — suggestive, not decisive — and the deficit followed a plantar nerve, not a nerve root. Ultrasound showed a distended tendon sheath narrowing the tunnel and no mass requiring excision. A diagnostic block dropped the burning for the duration of the anesthetic — supportive, not proof.

Hydrodissection changed almost nothing in the first weeks; they were told in advance to expect that. The shift came slowly — clearer by the second month, clearer again by the third, the same window in which the wrist trial separated from its control. Not immediate, and not complete. The first orthotic failed and had to be remade. Near five months the burning began to return, and a second hydrodissection was performed, with the understanding stated in advance that this is control measured in months. Individual results vary.

Frequently asked questions

Key takeaways

• Tarsal tunnel syndrome is compression of the posterior tibial nerve in a fibro-osseous tunnel at the inside of the ankle; because the heel branches usually leave above the tunnel, the sole burns while the heel can feel normal — the opposite of the plantar fasciitis pattern.
• The compression cascade taught in textbooks comes chiefly from animal models, and night pain is neural but not location-specific, so the diagnosis rests on differential work, not on the symptom alone.
• A normal nerve conduction study does not exclude the diagnosis; the supporting evidence for electrodiagnostics here is only Level C, and a diagnostic block localizes but does not confirm.
• Hydrodissection in the tarsal tunnel is investigational and off-label, supported by case series plus one blinded 34-patient trial in the wrist, where symptom scores separated from 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.

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.

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.

1. Char S, Jin MY, Francio VT, Hussain N, Wang EJ, Morsi M, Orhurhu V, Prokop LJ, Fink A, D’Souza RS. Implantable peripheral nerve stimulation for peripheral neuropathic pain: a systematic review of prospective studies. Biomedicines. 2022;10(10):2606. PMID: 36289867. https://pubmed.ncbi.nlm.nih.gov/36289867/

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

Dr. Gurpreet Singh Padda, MD, MBA, MHP