Electromyography is most useful electrophysiological study in the evaluation of lumbar compressive rediculopathy, However, electromyography may not be useful in mild motor root compressions without significant axon loss or in the initial 2~3weeks of severe motor root compressions with axon damage of in pure or mainly sensory root compressions.

In fact, signs of sensory fiver compromise alone are the most frequently observed in radiculopathy. After, that, signs of both motor and sensory fibers and signs of isolated motor fiber dysfunction are followng is descending order. The validity of useing the H-reflex to study the intergrity and conduction of the spinal monosynapic reflex arc has been documented.

We measured modified H-reflex test from tibialis anterior and peroneus longus muscles to diagnose the 5th lumber rediculopathy against a sample of 20 normal adults and 30 patients with clinical and radiological evidence of 5th lumber radicular compression, and got the following results and conclusions.

1) Abnormalities of modified H-reflex from tibialis anterior muscle in patient group are 23%(7/30), abnormalities of modified H-reflex from peroneus longus muscle in patient group are 60%(18/30). Therefore, the modified H-reflex study from peroneus longus muscle is more sensitive than that study form tibialis anterior muscle for the diagnosis of the 5th lumbar radiculopathy.

2) Abnormalities of modified H-reflex study from tibialis anterior and peroneus longus muscles in patient group with positive findings of only paravertebral muscles in electromyography are 50%(3/6).

We concluded that modified H-reflex study form tibialis anterior and peroneus longus muscles accompanied with electromyogragpy would be useful in the diagnosis of the 5th lumbar radiculopathy.