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.