During a voluntary contraction, the H-reflex could be obtained at lower stimulus intensities in the tibialis anterior muscle and a more clear separation of the H-wave from the M-wave was possible. The aim of choosing tibialis anterior is the relative ease in eliciting response over this muscle and the potential utility of this test in the evaluation of L4, L5 radicular compression, the latter being quite common in lumbar intervertebral disc prolapse.
H-reflex from tibialis anterior muscle (TAH-R) was recorded in 20 healthy subjects by averaging 100 responses from the maximal contracting tibialis anterior muscle after repetitive submaximal stimulation of common peroneal nerve. Subsequently, the test was applied to 22 patients with clinical and radiologic evidence of L5 or L4, L5 radicular compression. They were studied using stimulus intensity enough to produce just visible twitch in the muscle, stimulus duration of 1.0 msec, stimulus rate of 3 Hz and the muscle force to keep the foot in complete dorsiflexion as sufficient as possible. The take-off point was sharp and in no healthy subject was there any difficulty in measuring the latency to onset point. Abnormalities included significant right-left latency difference within the normal range of absolute latencies, unilateral or bilateral prolongation of latency to onset point and attenuation or absence of the response. Among the patients, 21 out of 22 cases of L5 or L4, L5 radicular compression had abnormal findings.
We concluded that the examination of the H-reflex from tibialis anterior muscle is easily performed and can be useful in the diagnosis of L4, L5 radicular compression.
