Tarsal tunnel syndrome (TTS) is an entrapment neuropathy not uncommonly encountered in clinical practice. There are two types of tarsal tunnel syndromes: anterior and posterior tarsal tunnel syndrome. Posterior TTS, the most common form, is entrapment of the posterior tibial nerve. Anterior TTS is entrapment of the deep peroneal nerve.
Clinicians should suspect the diagnosis of TTS when the patient complains of burning and/or numbness and pain at the sole, ball of the foot, or toes. A common finding includes a positive Tinel's sign posterior to the medial malleolus over the posterior tibial nerve. In a study by Oh, et al., 18-21 patients with TTS had a positive Tinel's tap. Gerow has suggested a modified Bragards test to aid in the differential diagnosis of TTS, where the test is performed without leg elevation exacerbating the patient's symptoms.
As the posterior tibial nerve passes behind the medial malleolus it divides into three branches: the lateral plantar nerve, medial plantar nerve, and the calcaneal nerve. The medial and lateral plantar nerves are separated by a septum and enter two separate tunnels distally. For this reason both nerves should be studied bilaterally when testing with electrodiagnosis methods. A branch of the lateral plantar nerve innervates the calcaneal periosteum and can be a cause of chronic unrelenting heel pain mistaken for a heel spur.
Etiologies of TTS include chronic ankle sprains, fractures, dislocations, post-traumatic fibrosis, ganglions, tendon sheath tumors, repetitive stress, and trauma such as jogging. Excessive stretch of the medial plantar nerve in joggers can cause TTS symptoms often referred to as "jogger's foot." In a study of 11 patients with TTS, Webb et al., found all 11 patients to have faulty foot mechanics, which was believed to be the primary etiology of TTS in his series of patients. Clinicians with sports practices should be alert to the diagnosis of TTS in their differential diagnosis of foot pain syndromes. There are other contributing and possibly predisposing factors. In a study by Dellon et al., many patients with the signs and symptoms of TTS had a co-existing polyneuropathy such as diabetes, superimposing the entrapment neuropathy. In these patients it appears possible, in my opinion, that a "double crush" type phenomena may exist, with the polyneuropathy predisposing the patient to TTS.
Electrodiagnosis of TTS is helpful in the differential diagnosis of radiculopathy, peripheral nerve entrapment, and polyneuropathy. Electrodiagnosis includes sensory and motor nerve conduction latency, velocity, and amplitude analysis (NCS), as well as electromyography (EMG). Delisa et al., has reported on the utility of adding orthodromic technique in addition to antidromic techniques. Delisa and others have published normal values for the NCS's of the medial and lateral plantar nerves, and may be found in reference texts. Controversy does not exist over the entity of TTS, but over the best way to confirm it electrodiagnostically. Some authors believe TTS to be primarily a focal demyelinative process, while others believe it to be primarily axonal. In a study by Byank et al., sensory distal latencies were the most frequent positive indicators of TTS, seen in over 80 percent of their cases. In the study by Oh et al., sensory NCSs were abnormal over 96 percent of the time with prolonged duration and slow conduction velocity. EMG abnormalities may include fibrillation potentials, and positive sharp waves in tibial innervated muscles.
Conservative management has been shown to be useful and is suggested prior to surgical decompression. A trial of extremity manipulation, transverse friction massage, adjunctive physiotherapies, and foot orthoses may provide relief. Patients should avoid jogging and hiking which may exacerbate their symptoms.
The clinical diagnosis of tarsal tunnel syndrome should be supported by electrodiagnostic methods, which can help differentiate radiculopathy, peripheral nerve entrapment and peripheral neuropathy. Lateral plantar versus medial plantar nerve involvement may be distinguished as well as if the lesion is primarily axonal or demyelinating. With this information the treating doctor can best provide a diagnosis, prognosis, and treatment plan.
References
Byank R. Neurometric eval in tarsal tunnel syn. Adv Ortho Surg 1989, Vol.12, 249-53.
Delisa JA. Tarsal tunnel syndrome. Muscle and Nerve 1983, 6: 664-670.
Delisa JA. Tibial nerve branching at the tarsal tunnel. Arch Neurol 1984, 41: 645-646.
Gerow G. Musculoskeletal System, Chp. 14 pg. 367-369 in: Chiropractic Diagnosis and Management, William & Wilkins.
Kaplan PE. Tarsal tunnel syndrome. J Bone Jt Surg. 1981: 63A: 96-99.
Murphy P. Clinics in Sports Medicine, 1985, vol 4, p. 753-762.
Oh S. Near nerve sensory NCV in tarsal tunnel syn. J Neur Neurosurg Psych. 1985, 18: 999-1003.
Spindler HA et al. Electrodiagnostic assessment in tarsal tunnel syn. Phys Med Rehab, August 1994, WB Saunders pg. 595-612.
Webb J. Tarsal tunnel syn. MED J Aust 1987, 147; 311-312.
David BenEliyahu, DC, DACBSP, DABCT
Selden, New York
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