Conventional electromyography provides useful informations such as distinguishing a peroneal neuropathy from an isolated L5 radiculopathy, identifying upper motor neuron lesion and determining the presence or absence of myopathy.

The purpose of this study was to identify the validity of tibialis anterior tendon reflex recorded by surface electrode for the diagnosis of isolated L5 radiculopathy, and to compare the responses between direct tapping of tendon(method A) and indirect tapping on wooden spatula that was placed on the dorsal and distal part of the first metatarsal bone(method B : Stam's method).

A control study was performed on 45 healthy Korean adults(mean age, 32.6 years old) to know the normal latency and amplitude, and to know the effect of height on latency recorded by surface electrode on center of tibialis anterior muscle. The 36 patients with proven compressive L5 radiculopathy by physical examination and various radiologic studies underwent the same studies.

The results were as follows;

1) In the normal control group, mean latency of the reflex by method A was 28.83±2.21 msec and there was no statistical difference between right and left leg. It was calculated that difference in latency up to 1.3 msec between two legs of a person was normal. Method B elicited latency of 29.98±2.01 msec and no statistical difference was found between right and left leg. The latency difference between two legs of a person up to 1.7 msec was considered to be normal.

2) In the normal control group, the latency obtained by method A and B was significantly correlated with height. And specificity of method A was higher(93.3%) than that of method B(86.6%).

3) In patient group, mean latency by method A were 28.51±2.21 msec on healthy leg and 31.36±3.11 msec on affected leg. The difference between them was statistically significant. Mean latency by method B were 30.51±1.53 msec on healthy leg and 32.45±2.18 msec on affected leg. The difference between them was also statistically significant.

4) In the patients group, the sensitivity of method A and B was the same (72.2%).

5) In the normal control group, mean amplitude of leg by method A was 0.38±0.37mV and there was no significant statistical difference between right and left leg. Method B elicited amplitude of 0.23±0.09mV. No statistical difference was found between right and left leg. The amplitude difference between two legs of a person up to 1.1mV and 0.2mV was considered to be normal in method A and B, respectively.

6) In patients group, mean amplitude by method A were 0.37±0.18mV on healthy leg and 0.29±0.14mV on affected leg. The difference between them was statistically significant. Average amplitude by method B were 0.31±0.15mV on healthy leg and 0.29±0.15mV on affected leg. The difference between them was not statistically significant.

Above results suggest that direct tapping on the tendon of tibialis anterior muscle provides a sensitive and specific electrodiagnostic results, and that in the electromyographic study to diagnose compressive L5 radiculopathy, this test could be helpful.