The H or F wave latencies in medial gastrocnemius in the electrodiagnostic study of sciatica patients with suspected S1 radiculopathy.

The aim of this study was to test H or F wave latencies of medial head of gastrocnemius muscle for electrodiagnostic evaluation of patients with suspected S1 radiculopathy with or without additional L5 radiculopathy. A group of 97 patients (34 female and 63 male), aged 20-60 (average 44 years), with clinically suspected unilateral radiculopathy were studied. Needle EMG of medial gastrocnemius muscle was supplemented by H or F wave latencies measurement bilaterally by percutaneous stimulation of tibial nerve in cubital fossa. EMG abnormalities indicating S1 radiculopathy were followed by H or F wave latencies abnormality in 63% of patients. The rest of 37% of patients of these group showed mild EMG abnormalities followed by normal H or F wave. Normal EMG finding was followed by normal H or F wave. Normal EMG finding was followed by normal H or F wave in 64% of patients. Increased latency of H or F wave without EMG abnormalities in gastrocnemius muscle was present in 36% of patients. The results of this study have proved that measurements of H of F latencies provide the objective evidence of S1 radiculopathy, presenting with the unilateral increase of latency or the absence of response. Abnormal H response latencies without EMG abnormality confirm the condition of sensory root affection only. Mild radicular affection in S1 distribution presented from early beginning or following recovery, was accompanied by normal H or F response, and therefore this test has prognostic value for the course of disorder.