Tarsal Tunnel Syndrome: Electrophysiological Study Shin J. Oh, M D , Palliyath K. Sarala, M D , Tadashi Kuba, M D , and Robert S. Elmore, M D
Tarsal tunnel syndrome (TTS)is a rare compression neuropathy of the posterior tibial nerve. Typical symptoms are burning pain and paresthesia in the toes and along the sole of the foot. T h e presence of Tinel's sign and objective sensory loss in the territory of any of the terminal branches of the posterior tibial nerve are diagnostically helpful. The terminal latency and sensory nerve conduction velocity in medial and lateral plantar nerves were studied in 20 normal controls and 21 cases of TTS in 17 patients. Prolonged terminal latency was observed in 11 cases, with TTS, while sensory nerve conduction abnormality (either absent nerve potential or slow sensory nerve conduction velocity) was found in 19. The sensory nerve conduction velocity in the lateral and medial plantar nerves is a superior objective diagnostic index of TTS. O h SJ, Sarala PK, Kuba T , et al: Tarsal tunnel syndrome: electrophysiological study. Ann Neurol 5:327-330, 1979
Tarsal tunnel syndrome ('ITS) in the foot is analogous to the well-recognized carpal tunnel syndrome in the wrist. Even though clinical studies of TTS are plentiful in the literature, electrophysiological studies are scarce [4, 6, 91. This paper reports an improved technique for detecting TTS by using the sensory nerve conduction velocity (NCV).
Materials and Methods Seventeen patients with TTS, 10 male and 7 female, were evaluated electrophysiolog~cally.Four patients had bilateral TTS, providing a total of 21 cases of TTS in the 17 patients. The duration of their symptoms ranged from three weeks to four years. In 9 cases of 'ITS the cause was not known. A past history of local trauma was observed in 6 cases: twisting injury to the ankle in 5 and fracture of the metatarsal bones in 1. Diabetes mellitus was the cause of 3 cases. In 2 cases, TTS developed after surgical procedures on the tarsal bones. Acromegaly was the cause of 1 case, and this patient also had carpal tunnel syndrome. Subjective burning and tingling paresthesia over the lateral o r medial plantar nerve territory and the presence of a Tinel sign on these nerves at the ankle were the diagnostic criteria of I T S in 19 cases. In 2 cases in which Tinel's sign was absent, the success of surgical relief of subjective and objective sensory impairments over the lateral or medial plantar nerve territory was the diagnostic criterion for TTS. Lumbar radiculopathy and peripheral neuropathy were ruled out by neurological and electrophysiological evaluations. To determine the motor terminal latency of the medial plantar nerve, the surface recording electrode was placed From the Department of Neurology, University of Alabama Medical Center, Birmingham, AL. Accepted for publication Aug 21, 1978.
o n the belly of the abductor hallucis muscle and the reference electrode o n its tendon. The ground electrode was placed o n the dorsum of the foot. The posterior tibial nerve was stimulated supramaximally by placing the stimulating electrode above the flexor retinaculum. The distance between the recording electrode and the stimulating electrode was kept constant at 10 cm. For the terminal latency of the lateral plantar nerve, the recording electrode was placed o n the belly of the abductor digiti quinti muscle of the foot. The distance between the stimulating electrode and the recording electrode was measured by caliper and was kept constant at I2 cm. Sensory nerve potential was recorded orthodromically by placing the recording electrode above the flexor retinaculum and by stimulating the great toe with ring electrodes for the medial plantar nerve and the little toe for the lateral plantar nerve. Sensory nerve potential in the lateral plantar nerve was not tested in the early part of the study; thus it was performed for only 18 cases of I T S in 15 patients. T h e 32 to 256 stimuli were averaged with a signal averager (DISA 14G).Latency was measured from the start of the stimulus to the negative peak of the nerve potential. Conduction velocity was calculated by dividing the distance by the latency. When n o recognizable and constant potential was noted after 256 stimuli had been averaged, we determined that there was no nerve potential. Skin temperature of the sole of the foot ranged from 27.5 to 32.5"C. Routine N C V of the peroneal, posterior tibial, and sural nerves was carried out in all patients. When the electrophysiological value in patients deviated more than 2 standard deviations from the normal mean, it was considered abnormal. Twenty normal hospital employees, ranging in age from
Address reprint requests to Dr Oh, Department of Neurology, University of Alabama Medical Center, University Station, Birmingham, AL j5294.
0364-5134/79/040327-04$01.25 @ 1978 by Shin Joong O h
327
19 to 50 years, volunteered as controls. Ten were female and 10 were male. Skin temperature of the sole of the foot varied from 29.5 to 33.5"C.
Results
A
Clinical Features The most common symptom of 'ITS was "burning tingling numbness" over the territory of the plantar nerves. One case produced pain that radiated proximally along the medial side of the calf. Three cases produced subjective complaints confined to the medial plantar nerve territory. In all patients, the symptoms were aggravated by activities such as prolonged standing or walking and were relieved by rest. Nocturnal exacerbation of pain was noted in 5 cases. Nineteen cases produced a Tinel sign; altered sensations to pinprick and touch over the plantar nerve territory were produced in 15 cases. Weakness of flexion of the toes was noted in 4 affected legs. Wasting of the intrinsic muscles of the foot was not recognized in any patient. Surgical decompression was carried out on 11 affected nerves; complete or considerable relief of symptoms was noted in 10. In 1 case the symptoms were relieved by local injection of steroid, while in others the symptoms persisted. Spontaneous improvement was never observed. The patient with acromegaly had clinical symptoms of right TTS at the time of the electrophysiological study, but also had a history of left 'ITS, which had been relieved after transsphenoidal abrasion of a pituitary tumor. Electrophysiologiral Studies
In t h e 20 normal controls the motor terminal latency for the medial plantar nerve was 4.10 ? 0.64 msec (mean SD), and for the lateral plantar nerve, 4.70 2 0.78 msec. Mean amplitude of the evoked muscle potential from the abductor hallucis was 7,540 pv, ranging from 3,500 to 22,000. Mean amplitude of the evoked muscle potential from the abductor digiti quinci was 7,250 pv, ranging from 3,000 to 10,000. Sensory NCV for the medial plantar nerve was 35.22 -t 3.63 mlsec (mean k SD), and mean amplitude of the nerve potential was 3.61 p v with a range of 2 to 6. Sensory NCV in the lateral plantar nerve was 31.68 ? 4.39 m/sec (mean ? SD) with a mean amplitude of nerve potential of 1.89 p v and a range from 1 to 5 (Figure). Among the 21 cases of 'ITS, prolonged terminal latency in the medial or lateral plantar nerves was observed in 11 (52.4%,): in 10 medial plantar nerves (>5.38 msec) and in 7 lateral plantar nerves P 6 . 2 6 msec). The amplitude of the evoked muscle potential was abnormally small in 7 medial plantar nerves (
Tarsal tunnel syndrome (TTS)is a rare compression neuropathy of the posterior tibial nerve. Typical symptoms are burning pain and paresthesia in the toes and along the sole of the foot. T h e presence of Tinel's sign and objective sensory loss in the territory of any of the terminal branches of the posterior tibial nerve are diagnostically helpful. The terminal latency and sensory nerve conduction velocity in medial and lateral plantar nerves were studied in 20 normal controls and 21 cases of TTS in 17 patients. Prolonged terminal latency was observed in 11 cases, with TTS, while sensory nerve conduction abnormality (either absent nerve potential or slow sensory nerve conduction velocity) was found in 19. The sensory nerve conduction velocity in the lateral and medial plantar nerves is a superior objective diagnostic index of TTS. O h SJ, Sarala PK, Kuba T , et al: Tarsal tunnel syndrome: electrophysiological study. Ann Neurol 5:327-330, 1979
Tarsal tunnel syndrome ('ITS) in the foot is analogous to the well-recognized carpal tunnel syndrome in the wrist. Even though clinical studies of TTS are plentiful in the literature, electrophysiological studies are scarce [4, 6, 91. This paper reports an improved technique for detecting TTS by using the sensory nerve conduction velocity (NCV).
Materials and Methods Seventeen patients with TTS, 10 male and 7 female, were evaluated electrophysiolog~cally.Four patients had bilateral TTS, providing a total of 21 cases of TTS in the 17 patients. The duration of their symptoms ranged from three weeks to four years. In 9 cases of 'ITS the cause was not known. A past history of local trauma was observed in 6 cases: twisting injury to the ankle in 5 and fracture of the metatarsal bones in 1. Diabetes mellitus was the cause of 3 cases. In 2 cases, TTS developed after surgical procedures on the tarsal bones. Acromegaly was the cause of 1 case, and this patient also had carpal tunnel syndrome. Subjective burning and tingling paresthesia over the lateral o r medial plantar nerve territory and the presence of a Tinel sign on these nerves at the ankle were the diagnostic criteria of I T S in 19 cases. In 2 cases in which Tinel's sign was absent, the success of surgical relief of subjective and objective sensory impairments over the lateral or medial plantar nerve territory was the diagnostic criterion for TTS. Lumbar radiculopathy and peripheral neuropathy were ruled out by neurological and electrophysiological evaluations. To determine the motor terminal latency of the medial plantar nerve, the surface recording electrode was placed From the Department of Neurology, University of Alabama Medical Center, Birmingham, AL. Accepted for publication Aug 21, 1978.
o n the belly of the abductor hallucis muscle and the reference electrode o n its tendon. The ground electrode was placed o n the dorsum of the foot. The posterior tibial nerve was stimulated supramaximally by placing the stimulating electrode above the flexor retinaculum. The distance between the recording electrode and the stimulating electrode was kept constant at 10 cm. For the terminal latency of the lateral plantar nerve, the recording electrode was placed o n the belly of the abductor digiti quinti muscle of the foot. The distance between the stimulating electrode and the recording electrode was measured by caliper and was kept constant at I2 cm. Sensory nerve potential was recorded orthodromically by placing the recording electrode above the flexor retinaculum and by stimulating the great toe with ring electrodes for the medial plantar nerve and the little toe for the lateral plantar nerve. Sensory nerve potential in the lateral plantar nerve was not tested in the early part of the study; thus it was performed for only 18 cases of I T S in 15 patients. T h e 32 to 256 stimuli were averaged with a signal averager (DISA 14G).Latency was measured from the start of the stimulus to the negative peak of the nerve potential. Conduction velocity was calculated by dividing the distance by the latency. When n o recognizable and constant potential was noted after 256 stimuli had been averaged, we determined that there was no nerve potential. Skin temperature of the sole of the foot ranged from 27.5 to 32.5"C. Routine N C V of the peroneal, posterior tibial, and sural nerves was carried out in all patients. When the electrophysiological value in patients deviated more than 2 standard deviations from the normal mean, it was considered abnormal. Twenty normal hospital employees, ranging in age from
Address reprint requests to Dr Oh, Department of Neurology, University of Alabama Medical Center, University Station, Birmingham, AL j5294.
0364-5134/79/040327-04$01.25 @ 1978 by Shin Joong O h
327
19 to 50 years, volunteered as controls. Ten were female and 10 were male. Skin temperature of the sole of the foot varied from 29.5 to 33.5"C.
Results
A
Clinical Features The most common symptom of 'ITS was "burning tingling numbness" over the territory of the plantar nerves. One case produced pain that radiated proximally along the medial side of the calf. Three cases produced subjective complaints confined to the medial plantar nerve territory. In all patients, the symptoms were aggravated by activities such as prolonged standing or walking and were relieved by rest. Nocturnal exacerbation of pain was noted in 5 cases. Nineteen cases produced a Tinel sign; altered sensations to pinprick and touch over the plantar nerve territory were produced in 15 cases. Weakness of flexion of the toes was noted in 4 affected legs. Wasting of the intrinsic muscles of the foot was not recognized in any patient. Surgical decompression was carried out on 11 affected nerves; complete or considerable relief of symptoms was noted in 10. In 1 case the symptoms were relieved by local injection of steroid, while in others the symptoms persisted. Spontaneous improvement was never observed. The patient with acromegaly had clinical symptoms of right TTS at the time of the electrophysiological study, but also had a history of left 'ITS, which had been relieved after transsphenoidal abrasion of a pituitary tumor. Electrophysiologiral Studies
In t h e 20 normal controls the motor terminal latency for the medial plantar nerve was 4.10 ? 0.64 msec (mean SD), and for the lateral plantar nerve, 4.70 2 0.78 msec. Mean amplitude of the evoked muscle potential from the abductor hallucis was 7,540 pv, ranging from 3,500 to 22,000. Mean amplitude of the evoked muscle potential from the abductor digiti quinci was 7,250 pv, ranging from 3,000 to 10,000. Sensory NCV for the medial plantar nerve was 35.22 -t 3.63 mlsec (mean k SD), and mean amplitude of the nerve potential was 3.61 p v with a range of 2 to 6. Sensory NCV in the lateral plantar nerve was 31.68 ? 4.39 m/sec (mean ? SD) with a mean amplitude of nerve potential of 1.89 p v and a range from 1 to 5 (Figure). Among the 21 cases of 'ITS, prolonged terminal latency in the medial or lateral plantar nerves was observed in 11 (52.4%,): in 10 medial plantar nerves (>5.38 msec) and in 7 lateral plantar nerves P 6 . 2 6 msec). The amplitude of the evoked muscle potential was abnormally small in 7 medial plantar nerves (
