The H-reflex has been used clinically to study diagnosis of the S1 radiculopathy. But only latency difference was used diagnostic criteria because of technical consistencies and the lack of normative data of the amplitude and the side to side difference.
In most of previous study groups, gastrocnemius muscle was used in evaluation of H-reflex. But in this study, we used soleus muscle in evaluation of H-reflex in order to establish more simple and more objective method of S1 radiculopathy diagnosis.
The H-reflex in the soleus muscle was evaluated in one hundred subjects(forty healthy subjects, thirty eight subjects having L5 radiculopathy and twenty two subjects having S1 radiculopathy).
An analysis of the regression of H-latency on height produced formula: H latency (ms)=11.24+0.12×Height(cm). Mean difference of H-latency was 1.07±0.44 ms in control group,1.18±0.34 ms in L5 radiculopathy group, 1.34±0.38 ms in S1 radiculopathy group(p<0.05). Mean difference of H-amplitude was 1.24±0.97 mV in control group, 1.22±0.84 mV in L5 radiculopathy group, 1.47±0.91 mV in S1 radiculopathy group(p<0.05). When we defined S1 radiculopathy as the latency over mean latency in control group+2SD, the sensitivity was 69.8%, specificity was 91.3%. And when we also defined S1 radiculopathy as the side to side H reflex latency difference over 1.5 ms, the sensitivity was 61.2%, specificity was 83.9%. In conclusion, the latency, latency difference & the amplitude difference of H reflex recording from soleus muscle are valuable tools in helping to diagnosis S1 radiculopathy.
