Electromyography in paraspinal muscles following surgery for root compression.

The paraspinal muscles were examined by electromyography (EMG) in 20 patients who had undergone laminectomy for root compression in the lumbosacral region. Cases were carefully selected to include only those in which there was no evidence of recurrent radiculopathy. The precise anatomic sites having electromyographic (EMG) abnormalities (fibrillation potentials and positive sharp waves) were determined. These data were obtained to determine if EMG of paraspinal muscles following laminectomy is useful in patients with a suspected recurrence. EMG was done 1 cm and 3 cm lateral from the midline at each vertebral level from L3 through S2. The interval between surgery and EMG ranged from 3-1/2 to 41 months. Seventeen of the 20 cases showed EMG abnormalities; and of these, 15 were abnormal at three or more vertebral levels and 13 at both 1 cm and 3 cm from the midline. It was shown that patients who have undergone laminectomy for root compression may demonstrate EMG changes in the paraspinal muscles for periods of up to 41 months postoperatively even without recurrent radiculopathy. The abnormalities are usually present at both 1 and 3 cm lateral from the midline and at multiple vertebral levels.