Tibial Neuropathy

Etiology

Tibial neuropathy can be caused by any condition that results in a lesion of the tibial nerve in the lower extremity. Trauma to the ankle is a major risk factor for the development of tibial neuropathy.[3] 

Ankle sprains and ankle fractures may result in scar tissue, bony fragments, or bone spurs which can place pressure on the tibial nerve. Similarly, trauma to the knee may cause damage to the tibial nerve, such as a posterior knee dislocation. Tarsal tunnel syndrome is compression of the tibial nerve as it travels under the transverse tarsal ligament. Other causes include lipomas, tumors, Baker’s cysts, and other space-occupying masses.[4] 

Some surgical procedures such as calcaneal osteotomy, performed for foot deformities, have been shown to have higher complication rates of tarsal tunnel syndrome.[5][6] There have been reported cases of tibial neuropathy secondary to anatomical variants in the muscles.[7]

Epidemiology

The incidence of tibial neuropathy is unknown. Isolated tibial neuropathy is a relatively uncommon diagnosis but can be seen post-trauma, in inflammatory conditions, and diabetes mellitus.[8] Tibial nerve lesions in the tarsal tunnel are seen at an increased incidence in patients with rheumatoid arthritis.[9]

History and Physical

The most common presenting symptoms of tibial neuropathy are pain and a change in sensation in the plantar aspect of the foot and toes. Commonly, there is also pain located around the medial malleolus where the tibial nerve runs. Symptoms can be exacerbated by passive ankle inversion. A key component of tibial neuropathy at the tarsal tunnel or distally is the sparing of sensation over the heel. This is because the calcaneal branch of the tibial nerve branches off proximal to the tarsal tunnel and, therefore, will not be affected in tarsal tunnel lesions.

The Tinel sign is tested by tapping over the suspected nerve entrapment site. A positive sign is indicated by the reproduction of pain and/or tingling in the distribution of the nerve. A positive Tinel’s sign can be seen at the ankle if the source of the pain is in the tarsal tunnel.[10] 

The patient’s gait should be evaluated, including heel walking, toe walking, and tandem gait. Overpronation may be seen with ambulation, which can place the tibial nerve under increased tension. If a proximal lesion of the tibial nerve is suspected, testing the gastrocnemius and soleus muscles is key to assessing for weakness. Given the strength of the plantar flexors, this is best assessed by having the patient perform one-legged calf raises if the patient can.

If tarsal tunnel syndrome is suspected, strength testing may be unreliable due to the difficulty in testing the intrinsic foot muscles on examination. Sensory testing should be performed, consisting of an evaluation of both pinprick and light touch. The patellar and Achilles reflexes should be compared from side to side, although this is a nonspecific finding that can also be seen in radiculopathy and polyneuropathy. In addition, these reflexes may not be involved depending on the location of the lesion. Tarsal tunnel syndrome generally does not affect the Achilles reflex.

Evaluation

Plain radiography is a useful starting point for suspected tarsal tunnel syndrome to identify potential fractures and osteophytes and evaluate overall foot structure. Computerized tomography (CT) and magnetic resonance imaging (MRI) of the lower extremity can help look for specific mechanical causes of tibial nerve damage such as local inflammation, mass lesions, or bony spurs. MRI, in particular, helps identify masses or tenosynovitis compared to CT.[11]

Ultrasound can provide a fast, dynamic study at the bedside to aid the diagnosis, particularly in suspected tarsal tunnel syndrome cases.[12] It is also helpful in ruling out other potential sources of the symptoms, particularly plantar fasciitis. If the plantar fascia is larger than 4.6 cm in thickness and hypoechoic, this is suggestive of plantar fasciitis. The tibial nerve can be visualized at the level of the medial malleolus and is hyperechoic. Color Doppler should be used to help identify the tibial artery and vein. The posterior tibialis and flexor digitorum longus tendons can be identified by their anisotropy.

Electrodiagnostic testing with nerve conduction studies (NCS) and electromyography (EMG) is a key component of diagnosing tibial neuropathy. Mixed or sensory studies of the medial and lateral plantar nerves should be performed. NCS will reveal decreased sensory nerve action potentials (SNAPs) in the medial and lateral plantar nerves. It is common for studies of these nerves to be difficult to obtain. The potentials of these nerves are often small in amplitude and require averaging.

It is not unusual to have unobtainable medial and lateral plantar nerve studies in normal patients. Therefore it is key to perform side-to-side comparisons in all suspected cases of tibial neuropathy. NCS will also reveal decreased compound motor action potentials (CMAPs) in the tibial motor nerve. The distal latencies of the abductor hallucis brevis and abductor digiti minimi muscles are important to compare from side to side to evaluate the medial and lateral plantar nerves. Hoffmann reflexes, as well as tibial and peroneal F responses, should be compared from side to side.[13]

EMG will show abnormalities in the tibial innervated muscles distal to the injury site. In tarsal tunnel syndrome, the plantar muscles in the foot will be affected. This includes abductor hallucis, adductor hallucis, flexor digitorum brevis, lumbricals, interossei, and quadratus plantae. If the tibial nerve is damaged more proximally above the ankle, then the medial and lateral gastrocnemius muscles may show signs of denervation. EMG can also help with diagnosing the chronicity of the injury. Fibrillation potentials and positive sharp waves may be present in acute tibial nerve injury, while polyphasic potentials and motor potentials with long duration and large amplitude may be seen in chronic injuries.[14]

Electrodiagnostic testing of tibial neuropathy is often technically difficult, particularly in cases of tarsal tunnel syndrome, due to difficulty isolating the distal portions of the tibial nerve. This is particularly evident in older patients. Abnormal EMG findings may be present in the intrinsic muscles of the foot in asymptomatic patients. It is extremely difficult to diagnose distal tibial neuropathy in the presence of superimposed polyneuropathy. Therefore, it is essential to correlate clinical history and physical exam with electrodiagnostic findings to avoid over-diagnosing cases of tibial neuropathy.

Treatment / Management

The treatment of tibial neuropathy depends on the severity of symptoms and nerve damage. Physical therapy is a key component of treatment for all cases of tibial neuropathy. A physical therapy treatment plan may consist of strengthening the tibial nerve innervated muscles. Nerve gliding exercises, kinesiology taping, electrical stimulation, and therapeutic ultrasound are just a few of the modalities that can aid with tibial neuropathy.[15] (A1)

Gait analysis can help identify contributing factors such as overpronation of the foot, which may place more tension on the tibial nerve. A medial heel insert can be placed in the shoe for cases of hyperpronation. Oral non-steroidal anti-inflammatory drugs can help with pain and inflammation. Gabapentin, pregabalin, duloxetine, and amitriptyline are frequently used medications for neuropathic pain. An ultrasound-guided corticosteroid injection into the tarsal tunnel or another area of compression can be beneficial for symptoms. 

Surgical intervention is indicated for more severe or refractory cases, particularly when muscle atrophy or severe weakness is present, as this is indicative of axonal nerve damage. The precise surgical technique varies based on the location of tibial nerve entrapment. Generally, it involves the release of the flexor retinaculum and fascia into the foot to release the medial and lateral plantar nerves.[16] Surgical outcomes are generally favorable if there is an identifiable cause of compression which can be localized.

Differential Diagnosis

Given the relative rarity of tibial neuropathy, more common causes of foot numbness, tingling, and pain should always be considered.[17]

Polyneuropathies from diabetes, alcohol use, or autoimmune causes must be ruled out. Frequently, an initial presentation of polyneuropathy is incorrectly diagnosed as tibial neuropathy due to the similarity of the symptoms. Lumbosacral radiculopathy can present similarly to tibial neuropathy, particularly in the L5 and S1 distributions. Sciatic nerve impingement or piriformis syndrome can also cause similar symptoms with more involvement of the proximal lower extremity muscles. Plantar fasciitis is a common cause of plantar foot pain that should be excluded, as it can present similarly to tibial neuropathy.[18][19]

Morton neuroma can cause pain under the metatarsal bones, which is burning or tingling, similar to a tibial neuropathy. Neurogenic or vascular claudication may also present with foot pain.

Prognosis

Prognosis can vary significantly in tibial neuropathy. Mild cases can respond well to conservative treatments such as therapy, orthotics, and over-the-counter anti-inflammatories. Although, if symptoms are severe or do not improve, further workup should be pursued. If the cause of tibial neuropathy is diagnosed and treated quickly, recovery is likely.

As with other neuropathic injuries, there can be residual pain and numbness depending on the degree of nerve injury. Prolonged nerve injury may result in significant weakness and atrophy in the tibial innervated muscles. Surgical intervention is less likely to succeed in larger tibial nerve lesions or patients requiring re-operation.[20]

Complications

Untreated or severe tibial neuropathy can result in persistent pain and weakness. There can be muscle atrophy and weakness of the tibial nerve innervated muscles in the flexor compartment of the foot. If the lesion is more proximal, there can be a weakness in the plantar flexors such as the gastrocnemius and soleus muscles.

Post-surgical complications include but are not limited to infection, bleeding, formation of scar tissue, and poor wound healing. Some cases of tibial neuropathy may have persistent symptoms despite surgical release.[21]