Tarsal tunnel syndrome, sometimes referred to as tibial nerve dysfunction or posterior tibial nerve neuralgia, is an entrapment neuropathy that is associated with the compression of the structures within the tarsal tunnel. It is similar to carpal tunnel syndrome of the wrist although much less common.
The tarsal tunnel is a narrow fibro-osseous space that runs behind and inferior to the medial malleolus. It is bounded by the medial malleolus anterosuperiorly, by the posterior talus and calcaneus laterally, and is held against the bone by the flexor retinaculum which extends from the medial malleolus to the medial calcaneus and prevents medial displacement of its contents.
The tarsal tunnel includes multiple important structures. It contains the tendons of the posterior tibialis, flexor digitorum longus (FDL), and flexor hallucis longus (FHL) muscles. The posterior tibial artery and vein, as well as posterior tibial nerve (L4-S3), also pass through it. The orientation of these structures within the tarsal tunnel is noteworthy. From medial to lateral, they are the tibialis posterior tendon, FDL tendon, posterior tibial artery and vein, posterior tibial nerve, and FHL tendon.
The posterior tibial nerve passes between the FDL and FHL muscles before it bifurcates in the tarsal tunnel, forming the medial and lateral plantar nerves. In 5% of people, the bifurcation occurs before the tarsal tunnel. The medial plantar nerve passes deep to the abductor hallucis and FHL muscles and provides sensation to the medial half of the foot and first 3.5 digits and motor function to the lumbricals, abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis. The lateral plantar nerve passes directly through the abductor hallucis muscle belly and provides sensory innervation of the medial calcaneus and lateral heel and motor function to the flexor digitorum brevis, quadratus plantae, and abductor digiti minimi. The medial calcaneal nerve typically branches off of the posterior tibial nerve proximal to the tarsal tunnel and provides sensory innervation to the posteromedial heel. In 25% of patients, it branches off of the lateral plantar nerve or runs superficial to the flexor retinaculum.
The mechanism of impingement can be identified in approximately 80% of cases.
The incidence of tarsal tunnel syndrome is unknown. It is a relatively rare and often underdiagnosed disease. It is higher in females than in males and can be seen at any age.
Tarsal tunnel syndrome results from the compression of the posterior tibial nerve or one of its two branches, the lateral or medial plantar nerve, within the tarsal tunnel. Up to 43% of patients have a history of trauma including events such as ankle sprains. Abnormal biomechanics can contribute to the disease progression. Risk factors include systemic diseases such as diabetes mellitus, hypothyroidism, gout, mucopolysaccharidosis, and hyperlipidemia.
There is no specific test for the diagnosis of tarsal tunnel syndrome, and diagnosis is made with a detailed history and clinical examination.
The predominant complaint is pain directly over the tarsal tunnel that radiates to the arch and plantar foot. Patients with tarsal tunnel syndrome will frequently report a sharp shooting pain in the foot, numbness on the plantar surface, radiation of pain and paresthesias along the distribution of the posterior tibial nerve, pain with extremes of dorsiflexion and eversion, and a tingling or burning sensation. These symptoms may localize to the medial ankle or plantar surface of the foot or be vaguer, making diagnosis difficult. Their symptoms will vary depending on whether the entire posterior tibial nerve is compressed or if it is the lateral or medial plantar branches. The symptoms may worsen at night, with walking or standing, or after physical activity, and typically get better with rest. Dysesthesias may worsen at night, disturbing sleep. The patient may note weakness in the muscles of the foot.
On exam, the provider may observe pes planus, pronated foot, or talipes equinovarus. In chronic cases, atrophy, weakness of the intrinsic foot muscles, and contractures of the toes may be appreciated. They are typically tender on deep palpation of the tarsal tunnel. The gait should be analyzed for abnormalities including excessive pronation or supination, toe eversion, excessive foot inversion or eversion, and antalgic gait.
Light touch and two-point discrimination should be tested. The patient may have diminished plantar sensation in the distribution of either the medial or lateral plantar nerve. Muscle strength and foot range of motion should be assessed. Strength deficits are typically a late finding in tarsal tunnel syndrome.
The Tinel test involves lightly tapping over the tarsal tunnel repeatedly. Pain or tingling in the distribution of the nerve is a positive test. Sensitivity is low at 25% to 75%; specificity is 70% to 90%. The dorsiflexion-eversion test involves passively dorsiflexing and everting the ankle to end range of motion and holding for 10 seconds. Reproduction of symptoms is a positive sign due to compression of the posterior tibial nerve in this position. This test is positive in 82% of patients with tarsal tunnel syndrome.
Tarsal Tunnel Syndrome Severity Rating Scale
A score of 10 indicates a normal foot and 0 indicates the most symptomatic foot.
Plain radiographs of the ankle and, possibly, the foot are the initial imaging study of choice. These may help identify any structural abnormalities including osteophytes, hindfoot varus and valgus, tarsal coalition, or evidence of previous trauma. MRI is not sensitive for the diagnosis of tarsal tunnel but may help include or exclude other causes of the patient's symptoms. Ultrasound can be used to evaluate the soft tissue structures. The nerve and its bifurcations can be observed. Either ultrasound or MRI can evaluate other soft tissue abnormalities including tendonitis or tenosynovitis, lipomas or other growths, varicose veins and ganglion cysts.
Electromyography (EMG) and nerve conduction studies (NCS) are frequently abnormal in patients with tarsal tunnel syndrome. Sensory nerve conduction studies are more likely to be abnormal than motor nerve conduction studies; however, the sensitivity and specificity are suboptimal. False negative tests are not uncommon and thus do not rule out the diagnosis.
Management of tarsal tunnel syndrome remains challenging due to diagnostic uncertainty and lack of clarity over which patients would benefit from conservative versus surgical management. Tarsal tunnel syndrome can be managed nonoperatively or operatively. This decision is generally guided by the etiology of the disease, degree of loss of function of the foot and ankle, as well as muscle atrophy.
Conservative management and success varies based upon the etiology of tarsal tunnel syndrome. The goal is to decrease pain, inflammation, and tissue stress. Ice can be used. Oral analgesics including acetaminophen and NSAIDs can be helpful. Neuropathic pain medications include gabapentin, pregabalin, and tricyclic antidepressants can be tried. Topical medications can also be used, including lidocaine and NSAIDs.
Physical therapy soft tissue modalities that may help include ultrasound, iontophoresis, phonophoresis, and E-stim. Calf stretching and nerve mobility or nerve gliding can also help with symptoms. Strengthening the tibialis posterior can help. Activity modification also plays a role in managing symptoms. Kinesiology tape can be used for arch support and biomechanical stress reduction.
Orthotic shoes can be used to correct biomechanical abnormalities and offload the tarsal tunnel. A medial heel wedge or heel seat may reduce traction on the nerve by inverting the heel. Night splinting can be tried, and patients who fail to respond to the above therapy can be placed in a walking boot temporarily. Footwear with appropriate arch support may help reduce symptoms. CAM (controlled, ankle, motion) walker or walking boots may be tried.
If a ganglion cyst is present, it can be aspirated under ultrasound guidance. Corticosteroid injections into the tarsal tunnel may help with edema.
Surgery is indicated if conservative management fails to resolve the patient’s symptoms or if a definitive cause of entrapment is identified. Patients with symptoms caused by a space-occupying lesion generally respond well to surgical management. Abnormally slow nerve conduction across the posterior tibial nerve is predictive of failed conservative therapy.
Surgical management involves the release of the flexor retinaculum from its proximal attachment near the medial malleolus down to the sustentaculum tali. Surgical success rates vary from 44% to 96%. Patient’s with a positive Tinel sign preoperatively tend to respond better to surgical decompression than those who do not. Younger patients and those with a short history of symptoms, early diagnosis, clear etiology, and no previous ankle pathology tend to respond better to surgery.
The differential diagnosis of tarsal tunnel syndrome is broad, making diagnosis difficult. This includes plantar fasciitis, intersection syndrome of the FHL and FDL at the knot of Henry, Achilles tendonitis, retrocalcaneal bursitis, polyneuropathy, L5 and S1 nerve root compression, Morton metatarsalgia, compartment syndrome of the deep flexor compartment, neurogenic intermittent claudication, degenerative changes (calcaneal spurs, arthrosis of the joints of the foot), and inflammatory conditions of the ligaments and fascia of the foot and ankle.
The prognosis of tarsal tunnel is variable. In patients with an identifiable etiology due to mass effect diagnosed early in the disease course, the response is generally favorable. Patients without an identifiable cause and who do not respond to conservative therapy generally do not do as well with surgical intervention. A positive Tinel sign is a strong predictor of surgical relief.
Untreated or refractory tarsal tunnel syndrome can result in neuropathies of the posterior tibial nerve and its branches. Patient’s may have persistent pain. Subsequent motor weakness and atrophy can develop. Postoperative complications include impaired wound healing, infection, and scar formation. Surgical decompression may not adequately resolve pain and other symptoms.
Postoperative rehab is aimed at protecting the joint and nerve integrity and controlling inflammation, pain, and swelling. As rehab continues, the therapist and patient work to prevent contraction and adhesions of scar tissue while maintaining soft tissue and joint mobility. Return to normal gait, walking, and running are long-term goals.
Tarsal tunnel is a difficult, rare diagnosis. As such, cases are best managed by an orthopedic specialist. Depending on the etiology, surgical management may be indicated.
There are no clear guidelines for the prevention or deterrence of tarsal tunnel syndrome.
Patients should be aware that there are many causes of foot and ankle pain, some of which are uncommon including tarsal tunnel syndrome. If a patient has foot and ankle pain as well as other concerning symptoms such as burning, numbness, tingling, and muscle weakness, they should seek the care of a medical professional.
Management of tarsal tunnel syndrome remains challenging due to diagnostic uncertainty and lack of clarity over which patients would benefit from conservative versus surgical management. Hence, the condition is best managed by a multidisciplinary team that consists of a podiatrist, orthopedic surgeon, and physical therapist.
Conservative treatment may help some patients but the key is physical therapy, change in shoes and modification of activity. For those with a compressive lesion, surgery may be beneficial.
The overall prognosis for patients with tarsal tunnel syndrome is guarded. Relapse and remissions are common and some patients never achieve complete relief from symptoms. (Level V)
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