Paraspinal denervation and the spinal degenerative cascade.

BACKGROUND CONTEXT: The aging of the spine has been reported to follow a degenerative cascade described by Kirkaldy-Willis. This cascade does not take into account the paraspinal muscles. Substantial recent knowledge of the anatomy, physiology and pathophysiology of the paraspinal muscles suggests that they should play a role in the degenerative cascade. Pain relates to paraspinal denervation in a number of disorders. Using new needle electromyographic technique, MiniPM, we may be able to quantify the extent of paraspinal muscle denervation.

PURPOSE: To explore the potential interactions between paraspinal muscle denervation and the degenerative cascade.

STUDY

DESIGN

Literature review, reanalysis of a blinded electromyographic study and case reports.

PATIENT SAMPLE: A previously reported group of 35 asymptomatic paid volunteers, ages 18 to 58 years. Two elderly volunteers with moderate to severe spinal stenosis on magnetic resonance imaging (MRI), one significantly disabled, one asymptomatic.

OUTCOME MEASURES: Blinded electromyographic testing, including MiniPM, a codified, quantified needle electromyography technique for the paraspinal muscles. In the two case reports, magnetic resonance imaging and 15-minute timed ambulation.

METHODS

The 35 volunteers were tested by a blinded electromyographer using the MiniPM technique. The two older subjects underwent MRI, MiniPM and extensive electrodiagnostic evaluations, functional testing, complete history and physical examination.

RESULTS

The patient with symptomatic stenosis had a MiniPM score of 6 on each side, and the asymptomatic volunteer had a score of 0. In the asymptomatic subject group, reproducible evidence for denervation was found in 20 subjects (57%), sparsely distributed, but more caudal than cranial (p<.0001). Based on conservative estimates of nerve regeneration rates, the population averaged a detected axonotemesis denervating event approximately once every 120 days.

CONCLUSIONS

Paraspinal denervation may be proven to be a better marker than MRI findings for symptomatic spinal stenosis. Subtle paraspinal muscle denervation occurs frequently in asymptomatic persons. Whether a cause or an effect, paraspinal denervation might lead to hypermobility and thus progression along the degenerative cascade.