Tarsal Tunnel Syndrome: Can A Minimally Invasive Release Be Advantageous?
Compression neuropathies of the posterior tibial nerve and its branches are a fairly common group of disorders, which are often misdiagnosed.1,2 In order to diagnose lesions of these nerves accurately, one must maintain a fairly high index of suspicion of their presentation. Relying on abnormal findings via electromyography and nerve conduction velocity testing is risky because the incidence of false negatives is quite high.2,3
In contrast, pressure specific sensory testing may produce false positive results. Although the classical presentation of tarsal tunnel syndrome involves compression of the posterior tibial nerve beneath the flexor retinaculum, more commonly, the compressed area is beneath the abductor hallucis muscle and primarily involves the medial calcaneal nerve. Since this nerve is a purely sensory nerve, nerve conduction testing is of little value.
Also bear in mind that tarsal tunnel syndrome is not a single entity. It encompasses compressive or traction injuries to the posterior tibial nerve and its terminal branches, the medial and lateral plantar nerves, as well as the medial and inferior calcaneal nerves.1,2,4,5
Since the site of injury can vary, symptoms will reflect this. For example, compression of the lateral plantar nerve will likely cause pain or numbness in the lateral forefoot while compression of the calcaneal nerves is associated with pain in the heel. Many patients who are diagnosed with plantar fasciitis and treated for that entity often have a poor response to treatment. There is a significant incidence of abnormal neurological findings in patients with chronic heel pain.1,3
Outcomes associated with the treatment of tarsal tunnel syndrome have not been universally favorable. Accordingly, there may be a collective reluctance among foot and ankle surgeons to engage in surgical decompression.3,6 Consider the traditional incision for this operation. The resultant scar follows closely after the incision, there is the course of the neurovascular bundle to contend with and the fact that the postoperative protocol immobilizes the foot and ankle. When one takes an objective view, it is easier to understand the high failure rate associated with this operation.
The development of a minimally invasive approach, which minimizes the risk of perioperative scarring and permits immediate movement with a rapid return to full activities, is something worthy of consideration.1
Salient Diagnostic Insights
When it comes to making the diagnosis of tarsal tunnel syndrome, I prefer to rely primarily on the history and physical examination. While the history may vary, the patient will usually relate a history of pain in the ankle, medial arch, heel or forefoot, which may be present upon first arising in the morning or following periods of rest. Sometimes the patient will describe waking up from sleep with complaints of pain or tingling when lying prone.
Patients may have difficulty describing their symptoms, particularly when it comes to localizing the area of pain or dysthesia. When the patient refers to pain in the forefoot or midfoot, and examination of the forefoot demonstrates a complete absence of confirmatory physical findings, the examiner should maintain a relatively high index of suspicion for the presence of an occult compression neuropathy.
There are four specific physical findings that may present when the posterior tibial nerve or any of its branches are irritated.1,2 One should test for numbness of any part or all of the sole of the foot by comparing the patient’s sensitivity to a light touch with the opposite foot. Physicians should regard the presence of a degree of numbness as a positive finding.
However, the absence of numbness while the foot is at rest does not preclude the presence of a compression neuropathy since compression of the posterior tibial nerve or any of its branches may only occur during weightbearing activities.