Testing for tarsal tunnel syndrome involves a combination of physical examination, nerve conduction studies, and sometimes imaging. No single test confirms the diagnosis on its own, and there is no universally standardized diagnostic algorithm. Instead, doctors piece together findings from several methods to build a clear picture of whether the tibial nerve is being compressed as it passes behind the inner ankle bone.
Physical Exam Tests
The first step is a hands-on examination. Your doctor will likely start with Tinel’s test: tapping repeatedly over the inside of your ankle, just behind the bony bump (the medial malleolus), where the tibial nerve runs through the tarsal tunnel. If tapping reproduces tingling, numbness, or shooting pain along the bottom of your foot, the test is considered positive. A positive Tinel’s sign is a strong predictor of good outcomes if surgery is eventually needed, but the test has limitations. Its sensitivity ranges from 25% to 75%, meaning it misses a significant number of true cases. Specificity is better, at 70% to 90%, so a positive result does carry weight.
The dorsiflexion-eversion test puts the nerve under stretch rather than direct pressure. Your doctor will passively pull your foot upward and outward while bending your toes back, then hold that position for five to ten seconds. If this reproduces your symptoms, it supports the diagnosis. Sometimes a positive Tinel’s sign will also trigger tingling that radiates upward toward the calf, a phenomenon called the Valleix sign, which further points to tibial nerve involvement.
Nerve Conduction Studies and EMG
Electrodiagnostic testing is the most widely used objective measure. About 80% of published studies on tarsal tunnel syndrome rely on nerve conduction studies (NCS) or electromyography (EMG), and nearly half of researchers consider abnormal results mandatory before making the diagnosis. These tests measure how fast and how strongly electrical signals travel through the tibial nerve and its branches.
During a nerve conduction study, small electrical impulses are applied to the skin over the nerve, and sensors record how quickly signals reach the muscles of the foot. A normal tibial nerve conducts signals at roughly 40.6 meters per second or faster. If the speed through the tarsal tunnel is at least 10 m/s slower than the speed measured along the lower leg above the tunnel, that’s considered a sign of compression. Recordings are typically taken from the muscle that moves your big toe and sometimes from the muscle controlling the little toe, since different branches of the nerve can be affected independently.
Sensory nerve conduction studies work in the other direction, stimulating above the tarsal tunnel and recording from the first or fifth toe. Sensory NCS has a reported median sensitivity of about 84%, while EMG (which measures the electrical activity of the foot muscles themselves to detect nerve damage) reaches a median sensitivity around 86%. These numbers sound encouraging, but reported sensitivities vary enormously across studies because of differences in technique, room temperature, electrode placement, and the thresholds each lab uses to define “abnormal.”
One professional association, the Association of Extremity Nerve Surgeons, has noted that traditional electrodiagnostic testing produces false negatives in up to 50% of cases. Their guidelines suggest these tests have questionable value as standalone tools, except when doctors need to rule out other conditions like a pinched nerve in the lower back. The practical takeaway: a normal nerve conduction study does not rule out tarsal tunnel syndrome.
Ultrasound
High-resolution ultrasound lets your doctor see the tibial nerve in real time and measure its size. A healthy posterior tibial nerve has a cross-sectional area of roughly 0.10 square centimeters, though published reference values range from 0.06 to 0.13 depending on the population studied. When the nerve is compressed, it changes shape from round or oval to flat, and it often enlarges above the compression site. Ultrasound can also reveal what’s causing the compression, such as a cyst, swollen tendon, or varicose vein pressing on the nerve.
The exam is painless and takes only a few minutes. Your doctor or a sonographer will place a small probe against the inner ankle and trace the nerve through the tunnel. The limitation is that ultrasound is highly operator-dependent, so the accuracy varies based on the experience of the person performing it.
MRI Findings
MRI provides the most detailed view of the structures inside the tarsal tunnel. In one study, MRI identified the compression site and the specific cause in over 82% of affected feet. It picks up space-occupying lesions like ganglion cysts or nerve tumors (schwannomas), but also reveals subtler causes. The most common finding in that study was a tortuous, winding posterior tibial artery pressing against the nerve. Other findings include inflamed tendons around the big toe flexor, varicose veins, fracture fragments, and soft tissue scarring from old injuries.
On MRI, compressed nerves appear brighter than normal on fluid-sensitive sequences. Radiologists look for at least 50% compression of the nerve’s diameter as the threshold for a significant finding. MRI is especially useful for surgical planning, since it tells the surgeon exactly where the compression is and what needs to be addressed. Across larger reviews, MRI has yielded significant findings in roughly 88% of patients with confirmed tarsal tunnel syndrome.
What Else Could It Be?
Part of testing for tarsal tunnel syndrome is ruling out other conditions that cause similar foot pain and tingling. Several common conditions overlap with its symptoms.
- Lower back nerve compression (S1 radiculopathy): A pinched nerve root in the spine can produce patchy numbness on the sole of the foot, usually on one side. Imaging of the lumbar spine and different patterns on nerve conduction testing help distinguish it.
- Plantar fasciitis: Causes heel and sole pain that is worst with the first steps in the morning and improves with activity throughout the day. Tarsal tunnel pain typically does not follow that pattern.
- Peripheral neuropathy: If symptoms are present in both feet symmetrically, generalized nerve damage from diabetes or other conditions is more likely than a localized tunnel compression.
- Morton’s neuroma: Produces pain and tingling between the third and fourth toes specifically, rather than across the whole sole.
- Metatarsal stress fractures: Common in runners, but the pain is usually on the top of the foot and localized to one spot.
- Rheumatologic conditions: Inflammatory diseases like rheumatoid arthritis cause ankle and foot pain on their own and are far more common than tarsal tunnel syndrome. They can also increase the risk of developing TTS, complicating the picture.
How These Tests Work Together
Because no single test is reliable enough on its own, diagnosis depends on combining a thorough symptom history, physical exam findings, and at least one objective test. A typical workup starts with the clinical exam. If provocative tests reproduce your symptoms, your doctor will likely order nerve conduction studies to confirm slowed conduction through the tunnel. If those come back normal but suspicion remains high, ultrasound or MRI can look for a structural cause. Diagnostic nerve blocks, where a local anesthetic is injected around the tibial nerve, are sometimes used as well. If the injection temporarily eliminates your symptoms, it strongly supports the diagnosis.
A 2025 systematic review found considerable variability in how doctors diagnose tarsal tunnel syndrome across clinical practice, with no consensus on which combination of tests should be required. The practical implication for you: if your initial workup is inconclusive but your symptoms persist, it’s reasonable to pursue additional testing rather than accepting a negative result from a single method.