A Closer Look At Tarsal Tunnel Syndrome
Symptoms associated with compression of the posterior tibial nerve and its branches first appeared in the literature in the early ‘60s.1-3 Since these early reports over 40 years ago, tarsal tunnel syndrome has become one of the most written about and discussed foot and ankle pathologies. Yet, even with the vast amount of literature on the subject, tarsal tunnel syndrome often remains somewhat elusive in regard to diagnosis and treatment. When inspecting the anatomy of the posterior tibial nerve, it is easy to appreciate why compression neuropathy may occur. Entrapment may occur proximally where the nerve lies between the deep and superficial fascia of the leg. As it courses distally closer to the medial malleolus, the fascia thickens and forms the flexor retinaculum, which overlies the nerve at this area. The nerve is further bound within its tunnel in this location by the medial surface of the tibia, talus and calcaneus. Fibrous septae from the retinaculum separate the nerve and posterior tibial artery from the flexor hallucis longus, flexor digitorum longus and posterior tibial tendons. The posterior tibial nerve divides into its two terminal branches (medial plantar nerve and lateral plantar nerve) deep to the flexor retinaculum in over 90 percent of cases. The medial calcaneal branch usually originates just proximal to or deep to the retinaculum. However, this branch may originate further distally. The medial calcaneal branch divides from either the posterior tibial nerve or lateral plantar nerve and is usually, although not always, a single branch.4 The medial and lateral plantar nerves then continue distally, deep to the abductor hallucis. The first branch of the lateral plantar nerve originates distally and is also a potential site of nerve entrapment between the deep fascia of the abductor hallucis and medial caudal margin of the quadratus plantae.5 Although the tarsal tunnel has been traditionally thought of as being only deep to the flexor retinaculum, it may extend anatomically both proximally and distally. Over 25 different etiologies are commonly discussed in the literature as contributing to the causation of tarsal tunnel syndrome. Some of the more common ones include overpronation or a valgus rearfoot, space occupying lesions including benign or malignant tumors, neuropathy (idiopathic or disease-related), trauma, arthritis, diabetes, various accessory muscles and posterior tibial tendon dysfunction. One of the more overlooked etiologies is the “double crush syndrome.”6 In this setting, a more proximal nerve injury may result in diminished axoplasmic flow, predisposing the nerve to be more easily compressed distally. What You Should Look For In Terms Of Key Clinical Findings The patient with tarsal tunnel syndrome may present with a variety of symptoms and it is this set of concurrent symptoms, which truly defines compression in the tarsal tunnel as a “syndrome.” Symptoms include combinations of burning, tingling, numbness over variable areas plantarly and/or sharp pain. More often than not, patients will describe the pain as diffuse but may be fairly specific in cases of space occupying lesions that produce isolated nerve compression. Extended standing or walking may aggravate symptoms. Conversely, some patients may experience night pain and find relief by becoming ambulatory. When examining a patient with tarsal tunnel syndrome, he or she may have a positive Tinel’s sign or Valleix phenomenon with percussion. It is usually somewhat difficult to actually demonstrate areas of discrete numbness plantarly. A significant decrease in two-point discrimination between the involved and uninvolved side has been reported in the literature.7,8 One may appreciate a motor deficit of the short flexors or abductor hallucis atrophy. You would also assess the deep tendon reflexes in order to help determine if there is proximal causation. Proceed to perform venous and arterial examinations in order to rule out venostasis or arterial insufficiency. Simple observation or palpation will reveal the presence of most space occupying lesions.