Tarsal tunnel syndrome is a compressive neuropathy of the posterior tibial nerve, or one of its branches, as it passes under the flexor retinaculum (ligamentum lacinatum) and/or under the adductor muscle of the first toe.
Clinical manifestations of tarsal tunnel
Patients present with heel pain, radiating or not to the lateral aspect of the heel or to the forefoot. There may be associated burning sensation, cramping, numbness or other paresthesias. Patients usually experience relief when removing shoes and socks or when they stop walking.
The pain may be at rest but may severely limit patients’ ambulation and they may not be able to walk moderate or short distances or play sports.
If we accept that 10% of the population (as opposed to 3-5% who have carpal tunnel syndrome) will have heel pain during their lives and that many of these cases are not plantar fasciosis, but peripheral neuropathies, it is possible that this is the most frequent peripheral neuropathy.
In many cases we see that patients have been suffering for years, up to 20 years, with heel pain falsely treated as plantar fasciosis, without any improvement.
Causes of tarsal tunnel syndrome
Although in 20-40% of the cases the cause is not determined, most of the time we find it in the compression of the posterior tibial nerve or in one of its branches in the tarsal canal.
The most frequent causes of tarsal tunnel syndrome are space-occupying lesions (post-traumatic, neoplastic or inflammatory). These include varicose veins (which are the most common), tenosynovitis, cysts or ganglions and neurilenomas. Less frequent are lipomas, neurofibromas or malignant tumors.
If we focus on post-traumatic factors, these account for 20% of cases. Some examples are ankle fractures, sprains or fractures and dislocations of the calcaneus or, more rarely, pseudarthrosis of the sustentaculum tali (which, if it migrates superiorly into the tunnel, can cause compression of the posterior tibial nerve). Bone anomalies, such as tarsal coalition, have also been described as causes of this syndrome.
On the other hand, this syndrome has been associated with systemic diseases, such as diabetes and rheumatoid arthritis, hypothyroidism, seronegative arthropathies and hyperlipidemias. Other less frequent causes may be muscle hypertrophy of the abductor digitorum primer, flexor digitorum longus or the existence of accessory muscles.
In addition, recent studies show that certain deformities, such as flat feet or a fixed valgus hindfoot, increase stress on the posterior tibial nerve.
A varus heel deformity with secondary foot pronation may also be implicated in the development of tarsal tunnel syndrome.
Diagnosis of tarsal tunnel syndrome
To diagnose tarsal tunnel syndrome, the most important is the clinical history and examination. Electromyography is negative in most cases, so this entity is underdiagnosed.
X-rays of the ankle and foot allow to evaluate the structure of the foot (flat foot, pes cavus), the existence of fractures, bony masses, osteophytes, as well as the coalitions of the subtalar joint. Laboratory studies will detect metabolic or rheumatic problems.
On the other hand, the Perthes test (compression with a tourniquet) causes occlusion of the superficial venous system; if the deep system is incompetent, the posterior tibial vein will fill and reproduce the symptomatology.
For its part, EMG allows examining the latency, amplitude and velocity of the posterior tibial nerve and its accompanying branches, while QST techniques quantify the perception of pressure and vibration.
MRI should be performed to rule out the existence of bone or soft tissue lesions leading to compression of the NTP.
The differential diagnosis should be made with L5 or S1 radiculopathy, or with a sensitive polyneuropathy (this is bilateral and has sock and Tinel distribution).
Tarsal tunnel syndrome treatments
The treatment of the tarsal tunnel syndrome must be directed to the cause that provokes the pathology (varicose veins, benign tumors, sequelae of fractures). If we suspect tenosynovitis or a local inflammatory process, we will use anti-inflammatory drugs, local infiltrations with corticoids, physiotherapy and rest orthosis.
- Ultrasound-guided infiltration of the tarsal tunnel. In cases of associated foot deformity, good results are achieved by reducing the tension created on the posterior tibial nerve.
Surgery is resorted to when these measures fail. Surgical release involves four steps: opening of the flexor retinaculum without posterior closure, opening of the fascia over the adductor of the first toe, exoneurolysis of the posterior tibial nerve and its branches along its entire length, and detachment of the fibroadipose septa of the medial calcaneal branch.
Minimally invasive techniques with endoscopic opening of the tunnel have been described and ultrasound is allowing the development of ultra-minimally invasive techniques for those cases in which there is no obvious cause of compression to be resected.
- Ultraminimally invasive ultrasound-guided surgery of the tarsal tunnel. The results are better when there is an objective cause that gives rise to the syndrome, than if it is idiopathic or post-traumatic. The results will be better the less time has elapsed.
The rates of good results published with conventional surgery vary between 50% and 90%. Recurrence of tarsal tunnel syndrome is difficult to treat and the results are less predictable. It usually occurs in older patients, with long-standing compression, due to double-level compression, inadequate surgical technique or the development of adhesions around the nerve.
In our opinion, longitudinal incisions on the tarsal tunnel induce a lot of fibrosis, and the rate of good results is not very good.
In case of open surgery, we believe it is better to make transverse incisions in the calcaneal malleolar axis, and to use magnifying glasses for release.
Ultraminimally invasive ultrasound-guided surgery is improving the results of open surgery and has added advantages, such as operating on both feet at the same time, no ischemia, no stitches and rapid recovery, although its limitations are yet to be defined.