Patients with tarsal tunnel syndrome present with pain in the inside of the ankle or heel region that radiates into the sole of their foot (Figure 1). 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. The pain occurs because tarsal tunnel syndrome 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 structures on the inside of the ankle (posterior medial structures including the branches of the tibial nerve) are placed under repetitive stress (Figure 2). Patients with irritation to the tibial nerve can be quite uncomfortable. Excessive walking and increased body weight can exacerbate the patient’s symptoms.
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. Tarsal tunnel is quite different than carpal tunnel syndrome! Carpal tunnel syndrome is seen in the wrist, where direct compression of the nerve produces the chronic injury and subsequent symptoms. The majority of diagnoses of tarsal tunnel syndrome are related to traction on the nerve. However, in small number of cases, there will be a physical mass, such as a bone spur or a ganglion that can press and injure the tibial nerve or its branches (Figure 3). Also, rarely the structures around the nerve are swollen or diseased such as inflamed tendons coursing along the tibial nerve and can affect the nerves similarly.
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 patients symptoms, 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.
It is also 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. This is important because local treatments may not be effective if the real problem is at the level of the low back.
Weightbearing x-rays of the foot should be assessed to review for any obvious pathology in the hindfoot. A CT scan or MRI is sometimes indicated to rule out a mass, which may be irritating the nerve (Figure 3).
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 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.
Tarsal tunnel release has been proposed as a treatment for tarsal tunnel syndrome. Operative treatment should be undertaken with great caution! Patients who undergo operative treatment can be left worse than they were prior to the surgery. This is because operative intervention involves surgery around the tibial nerve. This invariably leaves some surgical scarring around the nerve, hopefully (but not necessarily) with less compression on the nerve than what was there prior to surgery! In addition, operative treatment that only addresses the nerve will usually not address the underlying reason why the patient was having a repetitive or compression injury to the nerve in the first place.
Operative treatment typically involves a neurolysis of the tibial nerve. This means 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. This surgery will have a tendency to leave some scar by the nature of the operative insult. The hope is that more compressing tissue is removed than does recur.
It has been suggested that tarsal tunnel syndrome 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.
The main potential surgical complication that is specific to tarsal tunnel release is failure to eradicate the symptoms and in some cases, making the symptoms worse. Essentially, the nerve is often under traction and a strict freeing up of the nerve (neurolysis) will not do anything to address this. Furthermore, by operating around the nerve, any postoperative bleeding will have a tendency to scar the nerve further. The operation may leave the patient very hypersensitive in the area of surgery.
Other potential complications that are not specific to tarsal tunnel surgery include: