Posterior Tibial Nerve Entrapment: Tarsal Tunnel Syndrome

Tarsal tunnel syndrome is the entrapment of the posterior tibial nerve or one of its branches. This entrapment typically occurs within or distal to the tarsal canal, resulting in pain and/or sensory disturbance on the plantar aspect of the foot. Kopell and Thompson first reported entrapment of the posterior tibial nerve in 1960.21 In 1962, Keck and Lam independently used the term tarsal tunnel.22,23 Historically, tarsal tunnel syndrome was defined as the entrapment of the posterior tibial nerve in the fibro-osseous tunnel behind the medial malleolus, and the condition was considered to be rare. In time, however, the lateral plantar nerve and its branches were noted to be a more common site of entrapment. Patients typically present with intractable heel pain.

Tarsal tunnel syndrome is the most common entrapment neuropathy in the foot and ankle area. To differentiate the location of entrapment, some authors have used the term proximal tarsal tunnel syndrome to define entrapment of the posterior tibial nerve in the fibro-osseous tunnel behind the medial malleolus, and the term distal tarsal tunnel syndrome to denote entrapment of the distal branches, that is, the medial and lateral plantar nerves. In addition, others have more specifically identified entrapments involving the first branch of the lateral plantar nerve and the calcaneal nerves. However, the term tarsal tunnel syndrome is often used to define all entrapments of the posterior tibial nerve or its branches starting from posterior to the medial malleolus and extending distally.24

A slight female predominance has been reported in some studies, and the range of patient ages has been reported to be 14-80 years. This condition is common in nonathletes, although Baxter initially noted it in long-distance runners.25


The posterior tibial nerve (L4-S3) is a branch of the sciatic nerve. After entering the lower leg between the 2 heads of the gastrocnemius, the nerve is deep to the soleus muscle in the deep posterior compartment of the leg. The tibial nerve lies between the posterior tibial muscle and the FDL muscle in the upper leg; in the lower leg, it is between the FDL and the flexor hallucis longus. It then travels behind the medial malleolus, through the proximal tarsal tunnel, where it divides into its terminal branches, the medial and lateral plantar nerves. Havel and colleagues have shown that in 93% of cases, this bifurcation occurs within 2 cm of an imaginary line drawn between the middle of the medial malleolus and the midcalcaneus.26 Calcaneal branches, which have a highly variable anatomy, are present.

Most individuals (79%) have a single calcaneal nerve, usually arising from the posterior tibial nerve but sometimes arising from the lateral plantar nerve. About 21% have multiple calcaneal branches originating from the posterior tibial nerve, lateral plantar nerve, or medial plantar nerve, or from a combination of these. The calcaneal branches travel over the abductor hallucis muscle and supply sensation to the medial heel pad. The medial calcaneal nerve or nerves penetrate the flexor retinaculum and innervate the skin over the medial and posterior heel.

The tarsal tunnel is formed by the medial surface of the talus, the inferomedial navicular, the sustentaculum tali, and the curved medial surface of the calcaneus. The fibrous portion of the canal is the flexor retinaculum, also called the laciniate ligament. The retinaculum is formed by the deep and superficial aponeurosis of the leg and is attached closely to the sheaths of the posterior tibial, FDL, and flexor hallucis tendons.

Typically, a fibrous septum courses between the calcaneus and the deep fascia of the abductor hallucis muscle, and separates the medial and lateral plantar nerves just beyond their division from the posterior tibial nerve.

The first branch of the lateral plantar nerve travels between the deep fascia of the abductor hallucis and the medial fascia of the quadratus plantae and then continues deep to the flexor digitorum brevis muscle. Although somewhat variable, it has several branches. It typically provides a sensory branch to the medial calcaneal tuberosity, motor branches to the flexor digitorum brevis muscle, and sometimes a motor branch to the quadratus plantae. It then provides a sensory branch to the lateral heel and a motor branch to the abductor digiti quinti muscle.

Various anomalies have been reported, including the direct origination of all branches of the medial and lateral plantar nerves from the posterior tibial nerve.

The medial plantar nerve provides sensation to the medial half of the foot and the medial 3.5 digits. The nerve provides motor branches to the abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis, as well as to the first lumbrical.


Although tibial nerve entrapment can be seen anywhere along the course of the nerve, the most common location is distal to the ankle. Entrapments above the ankle have been reported in the popliteal fossa, where the nerve can be compressed by the tendinous arch of origin of the soleus muscle, a Baker cyst, or other masses that may occur in this region.

Compression of the posterior tibial nerve or one of its branches can occur because of intrinsic neural abnormalities or can result from external compression. External compression etiologies reported in the literature have included fibrosis, neurilemomas, ganglion cysts, lipomas, osteochondromas, varicosities, other benign and malignant tumors, tight tarsal canal, hypertrophic abductor hallucis, anomalous artery, and anomalous extra muscles (eg, the flexor digitorum accessorius longus). Other conditions that have been reported to contribute to the development of tarsal tunnel syndrome include tenosynovitis of the adjacent tendons, partial or complete rupture of the medial tendons, obesity, ankylosing spondylitis, acromegaly, and talocalcaneal coalition.

Several studies have suggested that compression of the posterior tibial nerve plays a role in the neurologic deterioration and loss of sensory and motor function in patients with long-standing diabetes mellitus. Wieman and Patel reported on 26 patients with painful diabetic neuropathy who underwent tarsal tunnel decompression, with pain improvement or relief in 24 (92%) of these patients within 1 month after surgery.27

Proliferative synovitis in conditions such as rheumatoid arthritis, which causes edema and compression of the tibial nerve in the tarsal tunnel, has also been reported. Direct blunt trauma to the nerve and traction injury to the nerve as a result of trauma or heel varus or valgus have been reported as well.

In the original case report and description of the condition in a patient with bilateral symptoms, Keck found tortuous posterior tibial veins surrounding the nerve, which he describes as resembling a varicocele.22 Since then, one of the most commonly encountered and reported causes of tarsal tunnel syndrome has been varicose veins.

Sammarco and Chang found that the most common surgical findings in 62 tarsal tunnel releases included arterial vascular leashes and varicosities, which cause indentation and scarring about the nerve.28 Cimino found that varicosities are the third most common cause of tarsal tunnel syndrome, as reported in the literature, and that idiopathic and traumatic causes are the first and second most common.29 Gould and Alvarez reported a case in which surgery revealed varicosities overlying the medial and lateral plantar nerves at their origin.30 Turan and colleagues also noted varicose veins more commonly than other compressive etiologies.31 The enlarged vessels crossing the nerve are theorized to cause direct compression of the posterior tibial nerve and its branches, particularly when the leg is in a dependent position.

Baxter and Thigpen described a biomechanical basis for the entrapment of the first branch of the lateral plantar nerve in the athlete.25 They proposed that entrapment results from the stretching and tethering of the plantar nerves, which are encased in the abductor hallucis deep fascial leashes, and from the hypertrophy of the small foot muscles, as well as from the increased forces in the hindfoot in the running athlete that create additional microtrauma to the runner's medial heel structures. They also noted that most of their patients with sports-related injuries had a normally arched or cavus-type foot.

Several authors have also reported increased valgus deformity of the foot to be a predisposing factor in chronic stretch injury of the posterior tibial nerve. Budak and coauthors noted prolonged distal latency of the medial and lateral plantar sensory nerves and delayed sensory conduction velocity of the medial plantar sensory nerve in patients with pes planus.32 Labib and colleagues reported on 14 patients who underwent surgical treatment for what they termed the heel pain triad.33 The triad consists of plantar fasciitis, posterior tibial tendon dysfunction, and tarsal tunnel syndrome. They postulated that failure of the static (plantar fascia) and dynamic (posterior tibial tendon) support of the longitudinal arch of the foot results in traction injury to the posterior tibial nerve. Trepman and coauthors reported increased pressure in the tarsal tunnel with the foot and ankle in full eversion or full inversion.34

Entrapment of the first branch of the lateral plantar nerve beneath the deep fascia of the abductor hallucis muscle and/or beneath the medial edge of the quadratus plantae fascia are the most commonly seen causes of tarsal tunnel syndrome.

Entrapment of the medial plantar nerve typically occurs in the areas of the master knot of Henry. It is seen most commonly in athletes; in 1978, Rask called it jogger's foot. It is theorized that excessive valgus or external rotation of the foot during running puts excessive stretch on the medial plantar nerve, resulting in tarsal tunnel syndrome. This condition has been seen in runners with flat feet who use corrective orthotics that can compress the nerve in the medial arch.


Patients with proximal tarsal tunnel usually present with diffuse, vague discomfort or pain. They may have burning, tingling, or frank numbness in the plantar foot. Although occasionally a history of trauma is reported, most patients present with insidious onset. Most patients have unilateral symptoms. Occasionally, patients may report proximal radiation of pain to the medial leg. Prolonged standing and walking usually exacerbate the symptoms, and rest improves symptoms. Many patients also present with night pain that is improved with massage or walking. Patients may note pain secondary to nerve tension when the ankle is placed in extreme dorsiflexion.

Patients with distal entrapment of the lateral plantar nerve or its branches usually present with chronic heel pain that has been present for 9-12 months. Many of their symptoms are similar to plantar fasciitis, especially the location of their pain and their startup pain. In addition to the mechanical symptoms of plantar fasciitis, they present with neuritic pain that is unrelated to weight bearing or loading of the foot.

Most patients report that their symptoms started exclusively when they were bearing weight. With time, the symptoms usually increase and eventually occur when the patient is seated; occasionally, they occur at night. Patients are usually asymptomatic in the mornings before taking their first step. Symptoms usually worsen with increased activity, as well as toward the end of the day and after long periods of standing, walking, or running. Prolonged standing in 1 place may be an aggravating factor. Most patients continue to have pain or burning ("after pain" or "after burn") for 30 minutes to several hours after they are off their feet.

Tarsal tunnel syndrome is seen commonly in individuals who are in their fifth and sixth decades of life, and it is more common in women than in men. Correlation with the patient's weight has not been found consistently. Most investigators have not been able to identify a significant common factor regarding occupation or underlying foot structure.

Some patients with tarsal tunnel syndrome have concomitant peripheral neuropathy or radiculopathy. Patients with peripheral neuropathy or radiculopathy may have symptoms that mimic tarsal tunnel syndrome.

Patients with certain systemic diseases, such as diabetes mellitus, alcoholism, thyroid disease, and vitamin deficiencies, are at increased risk for entrapment neuropathy.

Patients with medial plantar nerve entrapment usually present with pain in the medial aspect of the arch. They may have radiation of their pain to the medial toes and to the ankle. As with entrapment of the lateral plantar nerve, pain is worse with weight bearing. Occasionally, orthotic use may be correlated with the onset of the symptoms.

Inspection of the patient while the patient is standing and walking allows the examiner to evaluate for alignment deformities, such as hindfoot varus or valgus, swelling, varicosities, or other skin changes.

Palpation of the pulses is used to evaluate the patient's distal circulation. Sensory examination, including Semmes-Weinstein monofilament testing of the entire foot, may reveal dermatomal numbness due to compression neuropathy, or could reveal peripheral neuropathy. The range of motion of the ankle, subtalar, and the midfoot joints is examined, and any limitations are noted. The patient may report an increase in pain with dorsiflexion and eversion or inversion of the foot; Trepman and colleagues have shown these positions to increase the tarsal compartment pressure.34 Motor examination should include asking the patient to spread his or her toes so that an assessment can be made of the abductor digiti minimi or abductor hallucis and abductor digiti minimi muscles. Hypertrophy of the abductor hallucis muscle or an accessory muscle may also present, with fullness in the longitudinal arch.

Patients with proximal tarsal tunnel syndrome may have ganglia, tenosynovitis, or other space-occupying lesions in the tarsal tunnel that may be palpable. They may also have positive Tinel signs along the posterior tibial nerve. Occasionally, nerve percussion causes symptoms and pain to radiate proximally to the nerve course. This is known as the Valleix phenomenon. Linscheid noted that in most of his patients with proximal tarsal tunnel syndrome, manual compression of the nerve at the tarsal tunnel for 60 seconds reproduced their symptoms.35

Patients with distal tarsal tunnel syndrome usually have the most severe tenderness over the first branch of the lateral plantar nerve over the plantar medial heel and under the abductor hallucis muscle. Many patients have tenderness along the entire posterior tibial nerve, starting from behind the distal medial malleolus. Additional tenderness is usually present over the plantar fascia insertion on the medial calcaneal tuberosity and sometimes along the entire medial edge of the plantar fascia. The Tinel sign is usually absent.

The deep tendon reflexes and straight-leg raise are evaluated to look for isolated or concomitant radiculopathy. Hamstring tightness is evaluated with both legs extended.

Patients with entrapment of the medial plantar nerve have tenderness over the medial arch inferior to the navicular tuberosity, but not directly over the plantar fascia. Numbness and/or a Tinel sign over this area may be present only after prolonged weightbearing exercise. Stretching of the nerve as a result of eversion of the foot or of standing on the toes may also reproduce or exacerbate symptoms.

The diagnosis of tarsal tunnel syndrome (proximal and distal) is based primarily on a detailed history and physical examination. Plain radiographs should probably be obtained to exclude extrinsic factors, such as exostoses, malunions, or osteochondromas that cause direct nerve compression. In patients with posttraumatic symptoms, further investigation (eg, with CT scanning or MRI) are helpful in identifying occult sources of pain, such as medial talar process fractures, medial malleolus stress fractures, and space-occupying lesions. Further screening studies, such as laboratory workup for arthritides, diabetes, alcoholism, and thyroid dysfunction, are indicated in cases of associated inflammation and in patients with symptoms of peripheral neuropathy.

Electrodiagnostic tests are indicated in refractory cases or in cases in which the diagnosis is uncertain. A complete electromyographic and nerve conduction study of the motor and sensory nerves to the foot, with comparison to the other foot, is necessary. It is important for the electromyographic examination to include motor latencies, particularly to the abductor digiti minimi and abductor hallucis muscles, when tarsal tunnel syndrome is suspected.

Kaplan and Kernahan reported that reduced amplitude and increased duration of the motor response are more sensitive indicators of tarsal tunnel syndrome than is distal motor latency.36 Sensory action potentials may be affected in earlier stages than are motor fibers; therefore, changes may also be identified prior to any motor abnormalities. This is due to the fact that sensory fibers are more susceptible to injury. In addition, Kaplan and Kernahan believed that the lateral plantar branch of the posterior tibial nerve probably is affected earlier than is the nerve's medial plantar branch. Sensory studies are, therefore, considered to be the most sensitive studies for tibial nerve entrapment.

Galardi and colleagues reported that, after stimulation of the plantar nerves, the accuracy of the SNAP and mixed-nerve action potential are almost the same. SNAPs are more sensitive and less specific, and mixed-nerve action potentials are less sensitive and more specific. They concluded that the coexistence of mixed-nerve and SNAP abnormalities, especially if asymmetric, is highly indicative of tarsal tunnel syndrome. The mixed-response test is technically much easier to perform and better tolerated by many patients.

Approximately 90% of patients with tarsal tunnel syndrome have abnormal findings on electromyography and NCV studies. However, in the presence of supportive history and physical examination, a normal electrodiagnostic study does not exclude the diagnosis of tarsal tunnel syndrome. Electrodiagnostic tests, however, can be extremely helpful in diagnosing concomitant polyneuropathy, systemic disorders, and lumbosacral radiculopathy.

Positive results on electrodiagnostic tests are an affirmation of the diagnosis of tarsal tunnel syndrome. Golovchinsky reported a high incidence of double crush syndrome with overlapping of peripheral entrapment syndromes and signs of proximal nerve damage of the corresponding nerves (partial muscle denervation or abnormalities of the F wave).37 In such cases, simultaneous treatment of both problems may be indicated.


Treatment is directed toward the underlying etiology of neural compression. Nonoperative options can include the use of NSAIDs (in cases associated with inflammation), aspiration of underlying cystic lesions, and edema and varicosity control. Medical treatment of underlying systemic conditions is helpful in the indicated situation. The use of antineuritic medication, such as gabapentin and occasionally tricyclic antidepressants, has also been shown to improve symptoms in many patients.

At times, a trial of immobilization with the use of casts or walking boots is indicated. Orthotic management is indicated in patients with proximal entrapment and alignment or postural abnormalities causing chronic traction or compression trauma to the nerve. In patients with distal entrapment and associated heel pain, accommodative orthotics with a relief area in the anterior heel pad (ie, under the posterior tibial nerve) is usually helpful. Patients with flatfoot may benefit from semirigid University of California at Berkeley Laboratory (UCBL)–type orthotic devices with a deep heel cup to minimize weightbearing traction on the nerve.

Surgical release is indicated for refractory cases and for most cases with space-occupying lesions. The location of the release is partially dependent on the location of entrapment. Most cases, however, require a full release of the posterior tibial nerve and of the lateral plantar nerve and its branches. The skin is marked for the proposed skin incision. For proximal entrapment, the incision is started 2 cm proximal to the medial malleolus, approximately halfway between the medial malleolus and the Achilles tendon. It is extended distally and plantarly, directly superficial to the course of the posterior tibial nerve.

A full release includes release of the flexor retinaculum overlying the nerve, starting proximal to the medial malleolus and moving distally to include release of the deep fascia of the abductor hallucis muscle. The neurovascular bundle is posterior to the flexor digitorum brevis. Typically, medial and lateral plantar nerves branch at the level of the medial malleolus. It is best to identify the posterior tibial nerve proximally and follow it distally.

All sources of potential impingement are released from the medial and lateral plantar nerves. The medial calcaneal branches are quite variable and should be watched for closely. A large number of vessels are encountered routinely, and some crossing veins may need to be ligated. Ensuring full release of the lateral plantar nerve and its first branch is important. The superficial and deep fascia of the abductor hallucis is released as the nerve is followed distally. Partial release of the plantar fascia is usually necessary for full visualization. No consensus exists in the literature about the necessary amount of plantar fascia release.

The extent of the plantar fascia release may be dictated partially by the arch height, and a full release may be indicated in patients with a cavus foot, while minimal release could be considered in patients with flatfoot. Retraction of the abductor hallucis and the flexor digitorum brevis muscle allows good visualization of the lateral plantar nerve and its first branch. The usual course of the lateral plantar nerve is just anterior to the heel pad. As the lateral plantar nerve is followed, any compressive fascial bands are cut. The fascia of the quadratus plantae is also identified and released if it is noted to cause any compression by the medial edge of the quadratus plantae fascia on the first branch of the lateral plantar nerve. In cases of associated space-occupying lesions, the incision is modified as necessary for complete excision of the tumor.

Bipolar electrocautery and surgical loupe magnification are necessary for optimal visualization. It is important to minimize handling of the nerve. Often, large varicosities are present that should be considered as part of the underlying compressive etiology. Care should be taken to avoid injury to these large vessels, because such damage significantly compromises visualization and can cause intraoperative and postoperative bleeding, as well as postoperative scarring. The medial plantar nerve is fully released. The tourniquet is released prior to closure to ensure that no major bleeding occurs.

The plantar skin incision is reapproximated without the use of subcutaneous sutures. Reapproximating the subcutaneous tissues and the skin closes the medial segment of the incision. A bulky, soft-tissue dressing is then applied, and range-of-motion exercises are encouraged.

Postoperatively, the patient with a distal release of the nerve and full plantar fascia release is kept on nonweightbearing status for 4-6 weeks. In patients with lesser releases of the plantar fascia, weight bearing is protected until pain and swelling are improved and the wound is closed, which takes approximately 2-3 weeks. Complete release is indicated in most cases of tarsal tunnel syndrome, including those with distal entrapment of the nerve branches (which usually is associated with intractable heel pain).

If entrapment of the medial plantar nerve is suspected, the incision beyond the medial malleolus curves toward the plantar aspect of the medial navicular and full release is performed to the knot of Henry.

Baxter and Thigpen reported on 34 heels that underwent surgery in patients with recalcitrant heel pain.25 They performed a full release of the lateral plantar nerve and its branches with minimal or no plantar fascia release. The 2 most common areas of compression were noted at the sharp fascial edge of the abductor hallucis muscle and at the medial ridge of the calcaneus where the nerve passes over it beneath the tuberosity or origin of the flexor brevis and plantar fascia. They reported that 32 had good results and 2 had poor results. Most patients could detect improvement during the first or second postoperative day. Anti-inflammatory medication and orthosis use were continued postoperatively.

Watson and colleagues reported good-to-excellent results in 84% of patients who underwent distal tarsal tunnel release and partial plantar fasciotomy.38 Bailie and Kelikian reported that 84% of their patients in the noncompensation group were very or moderately satisfied with the outcome.39 They also reported better satisfaction in patients with nontraumatic etiology than in others. Sammarco and Chang subsequently reported on 108 ankles with tarsal tunnel syndrome.28 They found that patients with symptoms lasting less than 1 year had significantly better postoperative scores than did patients who had symptoms for more than 1 year before surgery. They did not observe an effect of trauma on the outcome of surgery, and reported that improvement was predictable even when a space-occupying lesion was not identified at surgery.

Tarsal tunnel syndrome is diagnosed primarily on the basis of the patient's history and physical examination. Electrodiagnostic studies support the diagnosis in about 80% of cases. Compression of the branches of the posterior tibial nerve is a common cause of refractory heel pain, and the most common compression neuropathy seen in the foot and ankle region. Nonoperative management of compression of the posterior tibial nerve involves relief of the source of external compression (if any), use of medication, and correction of weightbearing deformities. Surgical release in patients with proximal or distal entrapment has an 80-90% likelihood of improving or resolving the symptoms.

In one study, revision tarsal tunnel surgery was performed on 44 patients (2 bilaterally), including a neurolysis of the tibial nerve in the tarsal tunnel; the medial plantar, lateral plantar, and calcaneal nerves in their respective tunnels; excision of the intertunnel septum; and neuroma resection as indicated. A painful tarsal tunnel scar and a painful heel were treated, respectively, by resection of the distal saphenous nerve and a calcaneal nerve branch. Patient-satisfaction ratings were 54% excellent, 24% good, 13% fair, and 9% poor. Prognostic indicators of poor results were coexisting lumbosacral disc disease and/or neuropathy. The authors note that an approach related to resecting painful cutaneous nerves and neurolysis of all tibial nerve branches at the ankle offers hope for relief of pain and recovery of sensation for the majority of patients with failed previous tarsal tunnel surgery.