Tarsal Tunnel Syndrome (TTS) is caused by the compression or entrapment of the posterior tibial nerve within the tarsal tunnel, a narrow passageway on the inside of the ankle. Symptoms resulting from this nerve compression include pain, burning, numbness, or tingling sensations (paresthesia) affecting the sole of the foot or the toes. Misdiagnosis is common because the foot is complex, and nerve, bone, and soft tissue problems can produce similar discomfort. These neuropathic symptoms often overlap with issues originating outside the foot or from local structural damage.
Nerve Pain Originating Outside the Foot
Conditions where nerve irritation begins higher up the leg or is systemic throughout the body pose a significant diagnostic challenge. Lumbosacral radiculopathy, often called sciatica, is a common example. Nerve compression in the lower back, specifically involving the S1 nerve root, causes symptoms that radiate down the leg and into the foot. This can mimic TTS by causing pain, numbness, and tingling that extends to the heel and sole.
The distribution of pain is a primary differentiator. Radiculopathy involves pain that travels from the lower back or buttock down the posterior leg. Symptoms from a spinal source may also worsen with actions that increase spinal pressure, such as coughing, sneezing, or prolonged sitting. Electrodiagnostic testing, including Electromyography (EMG) and Nerve Conduction Velocity (NCV) studies, helps rule out radiculopathy by assessing nerve function along the pathway, including the nerve root.
Peripheral neuropathy, often seen in systemic diseases like diabetes, is another major mimic of Tarsal Tunnel Syndrome. This condition causes a diffuse, symmetrical pattern of tingling, numbness, and burning in both feet, often described as a “stocking-glove” distribution. Unlike the localized compression of TTS, peripheral neuropathy affects nerves throughout the body, making bilateral foot symptoms a strong indicator of a systemic issue.
Systemic conditions like diabetes or hypothyroidism can cause TTS by creating swelling or nerve damage, complicating the distinction between local entrapment and generalized neuropathy. Distinguishing between a primary entrapment (TTS) and a generalized neuropathy requires assessing the symmetry of symptoms and looking for other signs of systemic disease. The presence of bilateral symptoms or widespread sensory loss strongly suggests generalized neuropathy.
Localized Structural Causes of Foot Pain
Mechanical and structural conditions confined to the foot and ankle often produce pain confused with TTS. Plantar fasciitis is the most frequent misdiagnosis, as both conditions cause discomfort in the heel and arch. Plantar fasciitis is an inflammation of the thick tissue band on the bottom of the foot, and the pain is typically a sharp, stabbing sensation.
The timing of the pain is a key distinguishing factor. Plantar fasciitis is characteristically worst with the first few steps in the morning or after rest. In contrast, the burning and tingling of TTS often worsen with prolonged activity, standing, or at night when nerve pressure is sustained. True neuropathic symptoms like tingling or “pins and needles” are less common in plantar fasciitis, which primarily causes mechanical pain.
Tendinitis, specifically involving the posterior tibial tendon, can mimic TTS pain because the tendon passes through the same narrow tarsal tunnel. Posterior tibial tendon dysfunction (PTTD) causes localized pain and swelling along the inner ankle. The pain from tendinitis is typically reproduced by actively resisting the muscle’s movement, such as turning the foot inward against resistance.
Stress fractures cause a deep, persistent pain that can be confused with TTS discomfort. Stress fracture pain is purely mechanical, intensifying with weight-bearing activities and often accompanied by localized swelling and tenderness over the bone. The absence of burning, tingling, or numbness associated with nerve compression helps exclude Tarsal Tunnel Syndrome in these cases.
Differentiating Symptoms and Diagnostic Testing
Distinguishing TTS from its mimics relies on a detailed clinical history, a thorough physical examination, and targeted diagnostic testing. The physical exam often begins with the Tinel’s sign, where a provider gently taps the tibial nerve behind the medial ankle bone. A positive result reproduces the patient’s tingling or shooting pain into the foot, strongly suggesting localized nerve irritation at that site.
Two other provocative tests, the Dorsiflexion-Eversion Test and the Trepman test, are often used to stretch the tibial nerve and reproduce symptoms. The Dorsiflexion-Eversion Test has a high sensitivity for TTS. These clinical tests must be combined with an assessment of pain location and quality; for instance, sharp, localized heel pain that is worst in the morning points toward plantar fasciitis.
Electrodiagnostic studies, primarily Electromyography (EMG) and Nerve Conduction Velocity (NCV) studies, provide objective evidence of nerve dysfunction. NCV measures the speed and strength of electrical signals along the posterior tibial nerve and its branches into the foot. A prolonged nerve latency or reduced amplitude in the plantar nerves suggests compression within the tarsal tunnel.
EMG involves inserting a small needle electrode into the intrinsic muscles of the foot to assess electrical activity, helping to pinpoint if the nerve damage is motor-related and determine its severity. These electrical tests are highly valuable for ruling out higher-level nerve compression, such as lumbosacral radiculopathy, by comparing nerve function at different points.
Imaging studies are also employed. X-rays are used to check for structural issues like bone spurs or fractures. Magnetic Resonance Imaging (MRI) or ultrasound can visualize soft tissue masses, such as cysts or swollen tendons, that might be compressing the nerve within the tunnel.