Objective
Tarsal tunnel syndrome (TTS) is relatively rare and can be difficult to diagnose with conventional electrodiagnostic techniques. To increase the diagnostic sensitivity, we measured transtarsal conduction velocities of medial and lateral plantar nerves recorded by orthodromic near-nerve recording.

Method
Twenty normal subjects (aged 24∼59) were studied. For below flexor retinaculum (BFR) recordings, near-nerve needle recording electrodes were positioned posteriorly to the flexor digitorum longus tendon in medial plantar nerve and anteriorly to the calcaneus in lateral plantar nerve at the level of lower border of medial malleolus. For above flexor retinaculum (AFR) recordings, near-nerve needle recording electrodes were positioned anteriorly to the Achilles tendon 4 cm proximal to the BFR recording electrodes in medial and lateral plantar nerves. Stimulating ring electrodes were placed to the digit I and V.

Results
Transtarsal latencies and conduction velocities for medial plantar nerve were 0.7⁑0.1 msec, 56⁑6 m/sec, respectively. Transtarsal latencies and conduction velocities for lateral plantar nerve were 0.8⁑0.1 msec, 54⁑6 m/sec, respectively.

Conclusion
This approach may improve the diagnostic sensitivity in TTS.