The medical plantar nerve is the terminal sensory branch of the tibial nerve and the most distal nerve that is easily recorded in the lower extremities, but it is not generally included in nerve conduction studies of diabetic peripheral neuropathy. We recorded the orthodromic compound sensory and motor nerve action potentials of the medial and lateral plantar nerves across the tarsal tunnel in 47 adults aged from 22 to 78 (mean, 42.8 years) and studied those medial and lateral plantar nerves in 24 patients with diabwetes mellitus aged from 46 to 76 (mean 57.6 years). The compound nerve action potentials (CNAPs) were recorded from the posterior tibial nerve proximal to the flexor retinaculum and the medial and lateral plantar nerve were stimulated with a bipolar surface stimulator at a distance of 14 cm of the medial and lateral plantar surface of the foot, respectively. The normal distal latencies were 2.98⁑0.26 msec and the amplitudes 19.36⁑10.41 uV for the medial plantar mixed nerve and 3.05⁑0.28 msec and 10.42⁑5.18 uV for the lateral plantar mixed nerve. All the CNAPs of medial plantar nerve were evoked and in only 9.5% the potentials were not evoked in lateral plantar nerve. In patients with diabetes, the distal latencies of medial plantar nerve were 3.13⁑0.32 msec and the amplitude 11.67⁑4.89 uV, and those of lateral plantar nerve were 3.13⁑0.35 msec, 4.28⁑3.47 uV, respectively. In 55.3% of patients CNAPs were evoked in medial plantar nerves, and 14.9% for lateral plantar nerve. |