Paraspinal muscle denervation, paradoxically good lumbar endurance, and an abnormal flexion-extension cycle in lumbar spinal stenosis.

STUDY

DESIGN

A descriptive study was conducted to investigate the paraspinal muscle function in patients with lumbar spinal stenosis.

OBJECTIVE

To evaluate paraspinal muscle innervation and endurance in lumbar spinal stenosis.

SUMMARY OF BACKGROUND DATA: Abnormal lumbar paraspinal muscle function is associated with chronic low back pain. Abnormal neurophysiologic findings of the lower limbs often are observed in lumbar spinal stenosis, and abnormal lumbar function also can be expected. However, paraspinal muscle function and innervation have not been studied in lumbar spinal stenosis.

METHODS

The study evaluated 25 patients with clinically and radiologically diagnosed lumbar spinal stenosis. Electromyography of the paraspinal muscles was performed from L3 to S1 bilaterally using a concentric needle. At least 20 insertions were analyzed from each muscle. The aim of the examination was to detect abnormal spontaneous activity associated with axonal damage (fibrillation potentials, positive sharp waves, and complex repetitive discharges). Paraspinal muscle activity during trunk flexion-extension movement and muscle endurance during the dynamic isoinertial back endurance test were assessed by surface electromyography. Muscle fatigue was calculated using mean power frequency analysis.

RESULTS

Abnormal findings in needle electromyography of the paraspinal muscles were observed in 18 of the 22 (81.8%) examined patients. Abnormal flexion-extension activation of the paraspinal muscles was observed in all the examined patients. The change in mean power frequency was significantly smaller than in previously evaluated healthy subjects and patients with nonspecific chronic low back pain (P < 0.001) who were not experiencing symptoms of lumbar spinal stenosis. Paraspinal muscle fatigability was not associated with the denervation of the muscles. CONCLUSIONS Denervation and abnormal activation of lumbar paraspinal muscles are frequent findings in patients with lumbar spinal stenosis who have not undergone surgery. The paraspinal muscle endurance of the patients was unexpectedly good.