Tarsal tunnel syndrome happens when the posterior tibial nerve gets compressed as it passes through a narrow passageway on the inner side of your ankle. The causes range from acute injuries like ankle sprains to chronic conditions like arthritis or diabetes, but they all share the same basic mechanism: something reduces the already limited space inside the tunnel, squeezing the nerve. More than 2 in 5 people diagnosed with tarsal tunnel syndrome have a history of ankle injuries.
What the Tarsal Tunnel Actually Is
The tarsal tunnel sits just behind the bony bump on the inside of your ankle (the medial malleolus). It’s formed by bone on one side and a band of tough connective tissue, called the flexor retinaculum, stretching across it like a roof. Inside this small corridor, the posterior tibial nerve travels alongside tendons and blood vessels. The nerve branches within the tunnel into several smaller nerves that supply sensation to the sole and heel of your foot.
Because the tunnel is rigid, it can’t expand. Any swelling, growth, or structural change that takes up space inside or around it presses directly on the nerve. That compression is what produces the burning, tingling, and numbness characteristic of the condition.
Injuries and Overuse
Ankle sprains, fractures, and dislocations are among the most common triggers. When an ankle is injured, the resulting swelling puts pressure on the tibial nerve inside the tunnel. Even after the initial injury heals, scar tissue or lingering inflammation can continue to compress the nerve for weeks or months afterward. A badly healed fracture can also shift bone alignment enough to narrow the tunnel permanently.
For many people, tarsal tunnel syndrome develops not from a single event but from repetitive stress. Overuse injuries are a major contributor, particularly in runners, workers who stand on hard surfaces for long shifts, and anyone whose daily routine involves prolonged walking or impact on the feet. Repeated strain can cause the tendons running through the tunnel to swell, gradually crowding the nerve.
Growths and Structural Problems
Anything that physically occupies space inside or near the tunnel can compress the nerve. Ganglionic cysts (fluid-filled sacs that form near joints) are one of the more frequently identified culprits. Varicose veins around the ankle, known as venous stasis, can engorge blood vessels in the tunnel and create pressure. Bone spurs, lipomas (fatty growths), and benign tumors are less common but well-documented causes.
Foot structure matters too. Flat feet (overpronation) force the ankle inward during walking, which stretches and compresses the tibial nerve with every step. Over time, this repeated mechanical strain can trigger chronic inflammation of the tendon sheaths inside the tunnel, a condition called synovitis, which further reduces the available space.
Systemic Conditions That Increase Risk
Several whole-body health conditions can make the tarsal tunnel more vulnerable to compression, even without a clear injury or growth.
- Inflammatory arthritis: Rheumatoid arthritis causes inflammation of the synovial lining around tendons. When this affects the flexor tendons in the ankle, the swollen tissue presses on the nerve inside the tunnel.
- Diabetes: Diabetes makes nerves more susceptible to compression injuries because of reduced blood flow and metabolic changes in nerve tissue. People with diabetes may develop tarsal tunnel symptoms more easily and at lower levels of compression than others would.
- Hypothyroidism: An underactive thyroid can cause a mucus-like substance to deposit around nerves throughout the body, including the tibial nerve. This buildup mimics the symptoms of tarsal tunnel syndrome and may contribute to actual nerve compression.
Generalized swelling from conditions like heart failure or kidney disease can also increase fluid in the ankle area, adding pressure inside the tunnel. Pregnancy-related swelling occasionally triggers temporary symptoms as well.
When No Clear Cause Is Found
In a significant number of cases, no single identifiable cause emerges. The compression may result from a combination of subtle factors: mild flat feet plus a slightly thickened tendon sheath plus a job that requires hours of standing. Doctors sometimes call these cases “idiopathic,” meaning the exact trigger can’t be pinpointed, though the nerve compression is still real and measurable.
How It Feels Compared to Plantar Fasciitis
Because both conditions cause foot pain, tarsal tunnel syndrome is often confused with plantar fasciitis. The differences are distinct once you know what to look for. Plantar fasciitis produces a sharp, stabbing pain concentrated at the bottom of the heel, and it’s typically worst with the first steps in the morning or after sitting for a long time. Tarsal tunnel syndrome, by contrast, causes burning, tingling, or “pins and needles” sensations along the inner ankle and the sole of the foot. Numbness and muscle weakness in the foot are possible with tarsal tunnel syndrome but not with plantar fasciitis.
Tarsal tunnel symptoms tend to worsen during or after intense physical activity rather than after rest. In severe cases, the pain and numbness become constant. If you’re experiencing tingling or electrical sensations rather than purely sharp heel pain, nerve compression is a more likely explanation than a ligament problem.
How It Gets Diagnosed
Diagnosis typically starts with a physical exam. Your doctor may tap on the nerve behind your inner ankle bone to see if it reproduces tingling or pain shooting into the foot (similar to how tapping the inside of the wrist tests for carpal tunnel syndrome). Imaging like MRI or ultrasound can reveal cysts, swollen tendons, varicose veins, or other structural causes taking up space in the tunnel.
Nerve conduction studies, which measure how fast electrical signals travel through the nerve, are often used to confirm the diagnosis. These tests are highly specific, meaning a positive result is very reliable. Studies of the sensory nerve branches in the foot show specificity rates between 91% and 99%, depending on which branch is tested. However, the actual sensitivity of these tests, meaning their ability to catch every case, hasn’t been definitively established. A normal nerve conduction study doesn’t always rule out tarsal tunnel syndrome, particularly in early or mild cases.
What Happens if It’s Left Untreated
Prolonged nerve compression can lead to permanent nerve damage. Early on, symptoms come and go with activity. Over time, the tingling and numbness can become constant, and the muscles in the foot supplied by the affected nerve branches may weaken. This can change the way you walk and create secondary problems in the knee, hip, or back. Identifying and addressing the underlying cause, whether that’s a cyst, a structural foot problem, or chronic inflammation, gives the nerve the best chance of recovering before the damage becomes irreversible.