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.

Objective: To determine the reference values for the diagnosis of isolated entrapment neuropathies of medial and lateral plantar nerve and inferior calcaneal nerve distal to the tarsal tunnel.

Method: The subjects were neurologically healthy 30 adults (15 males, 15 females). Distal motor nerve conduction study of medial and lateral plantar nerves and inferior calcaneal nerve was performed. The recording muscles for medial and lateral plantar nerves and inferior calcaneal nerve were flexor hallucis brevis, flexor digiti minimi brevis, and abductor digiti minimi pedis, respectively. The stimulation was done at distal and proximal to the tarsal tunnel to differentiate the tarsal tunnel syndrome and the entrapment neuropathy of distal to the tarsal tunnel. The distance of recording and distal stimulation site was fixed to 10 cm for medial and lateral plantar nerves. The skin temperature was maintained 33^oC or above. The proximal latency, distal latency, peak to peak amplitude, conduction velocity and residual latency were measured. The reference values were obtained by 95 percentile values.

Results: The reference values for the diagnosis of isolated entrapment neuropathies of medial plantar nerve, lateral plantar nerve and inferior calcaneal nerve distal to tarsal tunnel are as follows.

1) Medial plantar nerve: distal latency, ＞ 4.3 msec; side to side difference, ＞ 0.7 msec

2) Lateral plantar nerve: distal latency, ＞ 4.1 msec; side to side difference, ＞ 0.6 msec

3) Latency difference of medial and lateral plantar nerve: ＞ 0.7 msec

4) Inferior calcaneal nerve: distal latency, ＞ 4.3 msec; distal peak latency, ＞ 7.2 msec; side to side difference of distal onset latency, ＞ 1.5 msec; side to side difference of distal peak latency, ＞ 0.8 msec; residual latency, ＞ 3.0 msec

Conclusion: The distal motor nerve conduction method used in this study and the reference values could be used to differentiate entrapment neuropathies of medial and lateral plantar nerve and inferior calcaneal nerve distal to the tarsal tunnel from tarsal tunnel syndrome.

Objective: The purposes of this study were to obtain the reference values of latency and amplitude of the medial plantar sensory nerve action potential(SNAP) in normal controls and to evaluate the diagnostic sensitivity of medial plantar sensory nerve conduction study(NCS) in diabetic neuropathy.

Method: Thirty healthy controls(mean age, 48.7 years; range, 38∼59 years) and 33 diabetic patients(mean age, 50.8 years; range, 37∼64 years) were included in this study. The inclusion criteria for diabetic patients were subjects with the normal peroneal and tibial compound muscle action potentials, obtainable sural SNAPs and intact pressure-perception to Semmes-Weinstein monofilament^Ⱂ 5.07.

Results: The medial plantar sensory nerve action potentials were obtainable in all control subjects and the reference values of onset latency and peak to peak amplitude were 4.29⁑0.49 msec and 3.1⁑1.34 ㄍV, respectively.

All 33 diabetic patients showed the normal latency and 3 of them showed the low amplitude in sural SNAPs. The medial plantar SNAPs were obtainable in 24 diabetic patients. Among 9 patients with unobtainable medial plantar SNAPs, 6 showed the normal sural SNAPs and 3 showed the low sural SNAPs. The sensitivities of medial plantar SNAPs to sural nerve and sural SNAPs to medial plantar sensory nerve were 100%(3/3) and 27.3%(3/11) respectively.

Conclusion: We concluded that medial plantar sensory NCS was more valuable in the early diagnosis of diabetic neuropathy than the sural NCS and Semmes-Weinstein monofilament^Ⱂ(North Coast Medical Inc, USA).