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Tarsal tunnel syndrome

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Description

Tarsal tunnel syndrome (TTS) refers to compression of the posterior tibial nerve in the tarsal tunnel. This can be due to many etiologies, including masses, trauma, and peripheral neuropathies. Tenderness of the tarsal tunnel, shooting pain, numbness, and tingling or burning sensations in the foot are common signs of TTS.

Structure and function

The tarsal tunnel is the space located posterior and inferior to the medial malleolus, lateral to the calcaneus and talus, and medial to the flexor retinaculum. Many structures run through the tarsal tunnel, including, from anterior to posterior, the tibialis posterior tendon, the flexor digitorum longus tendon, the posterior tibial artery, tibial nerve, and flexor hallucis longus (Figure 1). 

Figure 1: Anatomy of the tarsal tunnel (from www.orthoteers.com)

TTS affects the tibial nerve or its branches as they course under tight structures with limited space along the inner aspect of the ankle and down along the inner aspect of the heel and turning into the sole.There is some question as to whether this condition exists as an isolated entity as it is commonly seen in conjunction with other conditions such as plantar fasciitis and acquired adult flatfoot deformity. In all of these conditions, the posterior medial structures of the ankle structures on the inside of the ankle are placed under repetitive stress.  Repetitive injury to the tibial nerve can be due to a repetitive traction on the nerve, which creates some recurrent injury to the nerve and nerve sheath. This can lead to scarring of the nerve with resulting painful symptoms.  While the majority of diagnoses of tarsal tunnel syndrome are related to traction on the nerve, there are also cases where a physical mass, such as a bone spur or a ganglion, can press and injure the tibial nerve or its branches. Rarely the structures around the nerve are swollen or diseased such as inflamed tendons coursing along the tibial nerve and can also affect the nerves similarly.

Patient presentation

Patients with TTS typically complain of numbness in the foot radiating to the big toe and the first 3 toes, pain, burning, electrical sensations, and tingling over the base of the foot and the heel.  If the nerve entrapment is more proximal, the entire foot can be affected as varying branches of the tibial nerve can become involved. Ankle pain is also present in patients who have high level entrapments. Inflammation or swelling can occur within this tunnel for a number of reasons. The flexor retinaculum has a limited ability to stretch, so increased pressure will eventually cause compression on the nerve within the tunnel. As pressure increases on the nerves, the blood flow decreases. Nerves respond with altered sensations like tingling and numbness. Fluid collects in the foot when standing and walking and this makes the condition worse. As small muscles lose their nerve supply they can create a cramping feeling. 

 Patients with this condition present with pain in the inside of the ankle or heel region that radiates into the sole of their foot (Figure 2). This pain can have a sharp, shooting, dull, or burning feeling and may be associated with numbness. The pain is often worse with activity and towards the evening. Excessive walking and increased body weight can exacerbate the patient’s symptoms.


Figure 2: Location of pain in patient presenting with tarsal tunnel syndrome.(from footeducation.com http://www.footeducation.com/wp-content/uploads/2010/08/tarsal-tunnel-syndrome-Figure-1-300x235.png)

Objective evidence

Physical Exam

On physical examination, patients will often have a flatfoot type. Direct palpation over the inside of the ankle (posteromedial) will often reveal a localized area of pain with symptoms radiating into the sole of the foot. If direct pressure or tapping on the nerve reproduces patient symptoms and is described as an electric shock sensation, it is called a “Tinel’s sign”. Sensory examination of the foot may reveal some decreased sensation on the sole of the foot, although in most patients this is not the case.

Nerve conduction studies will often show a decrease in conduction of electrical pulses over the course of the tibial nerve.

Radiological evidence

Weightbearing x-rays of the foot should be assessed to review for any obvious pathology in the hindfoot. X-rays can rule out fractures, CT scan or MRI is sometimes indicated to rule out a mass that may be irritating the nerve, and ultrasound can be used to assess for synovitis or ganglia.


Figure 3: MRI showing fluid-filled ganglion (arrow) that is compressing the posterior tibial nerve. (from footeducation.com http://www.footeducation.com/wp-content/uploads/2010/08/Figure-3-Tarsal-Tunnel-Syndrome-Ganglion-Panchbhavi-04-19-2014.png)

Epidemiology

Though TTS is rare in commonality, causality can usually be determined in 70% of reported cases. According to a May 2014 OSHA report, in the workplace, TTS is considered a musculoskeletal disorder and accounts for 1.8 million cases a year, which accumulates to about $15–$20 billion a year ( Jeffress, Charles N. "Work-related Musculoskeletal Disorders (MSDs)." Work-related Musculoskeletal Disorders (MSDs). Occupational Safety & Health Administration, n.d. Web. 11 May 2014).  TTS occurs more dominantly in active adults, with a higher pervasiveness among women.

Differential diagnosis

It is important to attempt to determine the source of the problem.

  • Trauma
  • Space occupying lesion: ganglion cyst, benign tumors, swollen tendon, varicose veins
  • Ankle deformities: pes planus (flat foot)
  • Peripheral neuropathy: diabetes (if pain follows "stocking distribution")
  • Herniated lumbar disk: back pain in L4, L5, S1 regions, leg/thigh pain, "double crush"–one nerve pinch in the lower back, and the second in the tarsal tunnel.
  • Complex regional pain syndrome: if regional discoloration, swelling, temperature changes, allodynia, hyperesthesia
  • Neurofibromatosis: formation of pigmented, cutaneous neurofibromas can invade tarsal tunnel and create pressure.

Red flags

It is important to rule out nerve compression in the low back area. There is a fairly high correlation between nerve compression in the spine region (ex from a disk or spinal stenosis) and tarsal tunnel-type symptoms. If this is the case, then local treatments may not be effective if the real problem is at the level of the low back.

Treatment options and outcomes

Non-operative treatment

The vast majority of patients with tarsal tunnel syndrome can (and should) be treated nonoperatively. The primary approach to treating this condition is to attempt to decrease the repetitive traction injury across the nerve and the other structures in this area of the foot. In this regard, treatment is quite similar to that for acquired adult flatfoot deformity and plantar fasciitis. In fact, these three conditions (tarsal tunnel, acquired adult flatfoot, and plantar fasciitis) together have been labeled as the terrible triad and it is not uncommon to see them all together in one patient. This patient is typically someone with a flattened arch of the foot who is overweight.

  • Comfort shoes designed to disperse the force more evenly across the foot can be very helpful.
  • A prefabricated orthotic with a supportive arch will help to disperse the force more evenly across the foot may also be helpful.
  • Stretching exercises designed to stretch the calf muscle and thereby indirectly decrease the load through this area of the foot may also be helpful.
  • Weight loss will often end up being a critically important component of non-operative treatment, as this will serve to decrease the repetitive forces through this area of the foot.
  • Activity modification to limit the amount of standing and walking and thereby the amount of repetitive injury to this area is also an important component of nonoperative management. Physical therapy to establish exercise program characterized by appropriate fitness and stretching exercises, as well as some localized massage to help desensitize the area and perhaps breakdown scar may be of some benefit.
  • Corticosteroid injections may help to decrease the swelling around the nerve in the short and intermediate term. However, it is unclear what effect they have in the long term. In addition it is possible to injure the nerve during the injection process.
Operative treatment

Tarsal tunnel release has been proposed as a surgical option for treating tarsal tunnel syndrome. Additionally, operative treatment should also address the underlying reason for the repetitive or compressive injury to the nerve. Tarsal tunnel release (Figure 4) involves a neurolysis of the tibial nerve, which requires identifying and freeing up the tibial nerve as it passes the inside of the ankle and hindfoot. This is done by releasing any tight structures and removing any obvious scar on the outer aspect of the nerve. If there is a positive Tinel sign, then there is an 80% chance that decompressing the tarsal tunnel will relieve the symptoms of pain and numbness in a diabetic with TTS. It has been suggested that TTS in conjunction with a mass effect, such as a bone spur or ganglion cyst, may do better. In theory, removing the mass should help the patient’s symptoms. In practice, this is not always proven to be the case, because scarring can occur around the nerve during surgery, which may unfortunately also cause compression. Furthermore, by operating around the nerve, any postoperative bleeding will have a tendency to scar the nerve further. Thus the main potential surgical complication specific to tarsal tunnel release is hypersensitivity in the area of surgery, due to failure to eradicate the symptoms and in some cases, making the symptoms worse. Other potential complications that are not specific to tarsal tunnel surgery include wound healing problems, infection, deep vein thrombosis (DVT), pulmonary embolism (PE), and complex regional pain syndrome. 


Figure 4: Schematic of tarsal tunnel release (from Wikipedia: Tarsal tunnel syndrome)

Risk factors and prevention

Tarsal tunnel syndrome is known to affect both athletes and individuals that stand a lot. Strenuous activities involved in athletic activities put extra strain on the ankle and therefore can lead to the compression of the tibial nerve. Activities that especially involve sprinting and jumping have a greater risk of developing TTS. This is due to the ankle being put in eversion, inversion, and plantarflexion at high velocities. Examples of sports that can lead to TTS include basketball, track, soccer, lacrosse, and volleyball.

Neuropathy can occur in the lower limb through many modalities, some of which include obesity and inflammation around the joints. By association, this includes risk factors such as RA, compressed shoes, pregnancy, diabetes and thyroid diseases.

Miscellany

Tarsal tunnel is quite different than carpal tunnel syndrome as it is associated more with scarring and traction of the nerve rather more than direct compression. Carpal tunnel syndrome is seen in the wrist, where direct compression of the nerve produces the chronic injury and subsequent symptoms. 

Mnemonic for structures coursing through the tarsal tunnel (from anterior to posterior): Tom, Dick, and very nervous Harry. (Tibialis posterior tendon, flexor Digitorum longus tendon, posterior tibial Artery, posterior tibial Vein, tibial Nerve, flexor Hallucis longus tendon)

Key terms

posterior tibial nerve, Tinel's sign, terrible triad, adult acquired flatfoot deformity, pes planus, plantar fasciitis, tarsal tunnel release

Skills  

Recognize the Tinel's sign