Is the Tinel’s sign a reliable diagnostic test?
Tarsal tunnel syndrome describes an entrapment of the posterior tibial nerve at the medial aspect of the ankle. The posterior tibial nerve descends the leg and splits into three branches.
- First branch – supplies sensation to the plantar heel. Also called Baxter’s nerve.
- Second branch – supplies sensation to the plantar medial aspect of the foot.
- Third branch – supplies sensation to the plantar lateral aspect of the foot.
When diagnosing tarsal tunnel syndrome, the level of the entrapment and the branches affected by the entrapment can be diagnosed with a test called a Tinel’s sign (French neurologist Jules Tinel 1879-1952). Knowing the anatomical path of the posterior tibial nerve, use two fingers to percuss along the course of the nerve. When you identify a tingling sensation (paresthesia), this is likely the location of the entrapment.
Is a positive Tinel’s sign of the medial ankle a definitive diagnosis of tarsal tunnel syndrome? The answer is in many cases – maybe. First, there is no better test to diagnose tarsal tunnel syndrome. Therefore, a positive Tinel’s sign of the medial ankle and symptoms that are consistent with tarsal tunnel syndrome is the best we’ve got with today’s technology.
But let’s expand the use of the Tinel’s sign and test the deep peroneal nerve on the top of the foot. If you get a positive Tinel’s sign of the deep peroneal nerve, I start to think that I need to reconsider the validity of my posterior tibial nerve Tinel’s sign.
Now let’s go one step further. If you percuss the common peroneal nerve at the head of the fibula and get a positive Tinel’s sign, now I think you have a diagnostic dilemma. Let’s look a bit more closely at this diagnostic challenge.
When we map out the neuroanatomy of the lower leg, knowledge of the location of each of the branches helps you to isolate the most common areas of focal entrapment. So if you percuss at all three of the above described known areas of entrapment and only one results in a positive Tinel’s sign, odds are that’s the location of your problems. But when all three locations result in a positive Tinel’s sign, my thinking takes me more proximal (head north up the leg) and likely you’re dealing with a lumbo-sacral problem to include:
- Lumbar disc disease
- Lumbar stenosis
- Arthritis of the lumbar and sacral spine
- Metabolic issue including diabetes, thyroid disease
- Neurological diseases such as multiple sclerosis
- Neurotoxicity from chemical exposure or alcohol abuse
In the history that you take from your patient, it’s important to ask about a history of lumbar pain, recurrent injuries and lumbar surgery, general medical conditions, chemical exposures and alcohol use.
In summary, is the Tinel’s sign a good test to diagnosis tarsal tunnel syndrome? Certainly it is. But you also need to be sure to rule out other more proximal entrapment issues that may mimic the symptoms of tarsal tunnel syndrome.