Tarsal tunnel syndrome
By Katharine Leppard, MD, Medical Rehabilitation Specialists, Colorado Springs LIVING WELL Magazine
Tarsal tunnel syndrome is pinched tibial nerve at the inner ankle that causes pain and numbness on the bottom of the foot. This syndrome is analogous to carpal tunnel syndrome in the wrist, and was first described in 1962. Both tarsal tunnel and carpal tunnel are conditions where a nerve is pinched in a confined space. The tarsal tunnel is a narrow space at the inner ankle below the inner ankle bone called the medial malleolus. The tunnel has a bone base covered by a tough fibrous tissue called flexor retinaculum; this protects the structures inside the tunnel. Inside this tunnel there are several structures including the posterior tibial nerve, artery, vein and three tendons.
This posterior tibial nerve can be pinched, or squeezed, by a number of causes. This includes structures in the tunnel such as a ganglion cyst, bone spur, varicose veins, tumor or a swollen tendon, which can compress the nerve. An ankle sprain with swelling can injure the nerve. Conditions such as diabetes or arthritis have increased risk of tarsal tunnel syndrome. Abnormal biomechanics in the foot are also a cause. People with flat feet are at increased risk for tarsal tunnel syndrome, as a “fallen arch” can produce strain and compression of the tibial nerve at the inner ankle.
Typical symptoms include tingling, pins and needles, burning and sometimes electric shock sensations on the bottom of the foot. There can be pain at the inside of the ankle, the heel or the arch of the foot. This pain is sometimes worse at nighttime; pain can also increase with standing and weight bearing. There is no tenderness on palpation of the arch, although this is an area where pain is experienced. With severe tarsal tunnel syndrome, weakness occurs in great toe flexion, and also in spreading the little toes.
There are a number of conditions that cause foot pain and can mimic tarsal tunnel syndrome, and accurate diagnosis is critical. The differential diagnosis includes plantar fasciitis, heel spurs, peripheral neuropathy and arthritis––to name a few conditions.
Plantar fasciitis is a common cause of pain in the arch of the foot and the heel. The plantar fascia is a thick fibrous band on the bottom of the foot. It starts at the heel bone and fans forward towards the toes, and acts like a bowstring to maintain the arch of the foot. Classically, this pain is worse in the morning with the first few steps, after sitting, standing or walking. Plantar fasciitis should not have numbness on the bottom of the foot. Treatment for plantar fasciitis includes orthotics, ice, anti-inflammatories, sleeping in a boot, injections and surgery.
A heel spur is a bone spur that develops on the heel where the plantar fascia connects to the bone. Heel spurs can be seen in people with no pain, and whether or not the heel spur is the primary problem or the plantar fasciitis is the problem remains a question.
Peripheral neuropathy can also cause foot pain and numbness. And it is not unusual for symptoms to begin on one foot, before starting on the other foot. Peripheral neuropathy is a generalized dysfunction of the nerves, which causes variable symptoms including toe and foot numbness, pain, and balance difficulty. It can also affect the hands. If a peripheral neuropathy is diagnosed, it is important to rule out treatable causes of peripheral neuropathy including thyroid disease, undiagnosed diabetes, and vitamin B12 deficiencies. A large number of peripheral neuropathies have no clear identifiable cause, these are called an idiopathic peripheral neuropathy. Peripheral neuropathy is a common condition, it is estimated that 20 million people in the United States have peripheral neuropathy.
Testing for tarsal tunnel syndrome includes physical examination. Taping on the nerve can reproduce the symptoms or trigger an electric sensation radiating to the bottom of the foot, which is called a Tinel’s sign. An EMG study is an important diagnostic test. The EMG study consists of two components. Nerve conduction studies are the first component of an EMG study. In nerve conduction studies, a small electrical signal is applied over the nerve, and the examiner measures how quickly and how well the nerve carries that signal. Healthy nerves are very fast and have nice large responses. Peripheral neuropathy nerves become slow, and can have small and even absent responses. In tarsal tunnel syndrome, the tibial nerve conduction studies are abnormal. The second component of an EMG study is electromyography. Here, a small pin with a microphone on the tip is inserted into strategic muscles innervated by different nerves to examine the electrical activity in the muscle. This gives information not only about the muscle function, but also the nerve that innervates that particular muscle. EMG studies are currently the best test for tarsal tunnel syndrome; however, there can be false-negative test results. This means that the test is normal, but the condition is truly there. Advanced imaging studies such as an MRI scan can be performed as well.
Treatment options for tarsal tunnel include orthotics, changing footwear, ice, immobilization, anti-inflammatory medications, physical therapy, cortisone injection, and surgery.
Tarsal tunnel syndrome is an uncommon pinched nerve. It can lead to significant pain, numbness on the bottom of the foot and weakness in great toe flexion and spreading of the little toes. Numbness in the feet is not normal; it is not a normal sign of aging, and should be evaluated. Foot pain can be due to a myriad of reasons, and accurate diagnosis is critical.
Dr. Leppard is with Medical Rehabilitation Specialists and may be reached at 719-575-1800.