The H-Reflex Of Biceps Femoris Muscle

Introduction. H-reflex is typically recorded from limb muscles with stimulation to a mixed peripheral nerve, such as the tibial nerve and median nerve. H-reflex can be elicited from the soleus muscle by magnetic or electrical stimulation. This application provides a method for distinguishing between proximal and distal lesion sites of the reflex pathway subserving the soleus muscle. With stimulation to the S1 nerve root, H-reflex can be elicited from the soleus and a variety of other muscles. This technique provides a distinct approach in human spinal reflex study. The present study reports a method of eliciting biceps femoris H-reflex and the measures of latency and amplitude of Biceps Femoris H-reflex in normal subjects. In this study, we also studied the utility of the biceps femoris long head H-reflex (BFL H-reflex) in diagnosing lumbosacral radiculopathy.Methods. We studied 32 normal subjects and 35 patients with surgically confirmed S1 or L5 radiculopathy. Electrical stimulation of the S1 nerve root was performed with a high voltage electrical stimulator, the Digitimer D180, which produced a brief 0.1ms capacitance applied through 1cm diameter electrode.The cathode was placed on the skin overlying the S1 foramen and the anode on the abdomen at the same level. The intensity used was adjusted to elicit the Hmax for that individual.M wave and H wave were recorded from the belly of biceps femoris (long head) with surface electrodes. A short distance of 3 cm between the active and reference electrodes was applied to reduce the duration of the M wave for a clear separation between the M and H waves. Baseline-to-peak amplitude of the potentials was measured. Latency was measured at the peaks of the M and H waves. H-M interval was calculated.In the three subjects, we tried to let the subjects to flex slightly the knee joint for a single 3-5s phasic contraction of the homonymous agonist muscle, meanwhile we stimulated the S1 root and recorded the H-reflex from the BFL muscle. In the other three subjects, we vibrated on the tendon of the biceps femoris (long head) for about 30s, then we tried to stimulate the S1 root and record BFL H-reflex while the vibration is continuing. We also compared the difference of the bilateral H-M intervals. We judged the change of the H-reflex in patients with the L5 or S1 radiculopathy.Results. Electrical stimulation of S1 nerve root at the S1 foramen evoked in the biceps femoris muscle two distinct potentials separated by 6.85±0.65ms. The initial potential is the M wave, with the latency of 6.70±0.76ms in average. The second potential is the H-reflex. The side-to-side difference of the H-M interval is 0.24±0.18ms in average, so the side-to-side difference of the H-M interval in the normal subjects must be less than 0.6ms.Increasing the stimulus intensity was accompanied by a progressive increase in the amplitude of both M and H waves and led to a subsequent decline in the H-reflex amplitude while the M wave continued to grow. The Hmax in two patients with unilateral S1 radiculopathy was approximately 2-3mv.In the subjects with phasic contraction, the Peak-to-baseline amplitude of the facilitated H-reflex is significantly higher than the H-reflex recorded from the subject in the rest, while the amplitude of the M-wave did not have much more change. In the subjects with vibration, vibration has been shown to markedly reduce the peak-to-baseline amplitude of the BFL H-reflex. But vibration did not significantly reduce the M-wave. There was no significant difference in latency obtained for the BFL H-reflexes under the condition S1 root stimulation.BFL H-reflex was prolonged(the difference of the side-to-side H-M interval>0.6ms) or absent in most patients with S1 radiculopathy, as the H-reflex of the soleus muscle. However, in patients with the L5 radiculopathy, almost bilateral BFL H-reflexes were normal and the difference of the side-to-side H-M interval was less than 0.6ms. Only one patient with S1 radiculopathy had normal BFL H-reflex in the involved side. Conclusions. H-reflex can be recorded from the biceps femoris muscle following stimulation of the S1 nerve root in normal adults. The H-M interval recorded from the biceps femoris is equal to that from the soleus muscle, which provides a reliable measure of conduction of the S1 nerve root within the spinal canal including proximal afferents, anterior horn cells and ventral roots subserving the biceps femoris muscle. Biceps femoris H-reflex might be useful in studying S1 radiculopathy.BFL H-reflex is a promising technique in the study of lombosacral radiculopathy, whose sensibility is higher than the traditional tibial H reflex and its false positive is lower than the Sol H-reflex.