DOI: 10.1097/bn9.0000000000000147 ISSN: 3066-8905

Discogenic Evoked Multifidus Motor Unit Action Potential Inhibition From Impulsive Lumbar Spinal Manipulation

Christopher J. Colloca, Aage Indahl, Robert Gunzburg, Marek Szpalski, Mostafa A. Hegazy, Richard Hinrichs
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Study Design:

Controlled, repeated-measures porcine basic science experiment with three randomly applied within-subject mechanical interventions.

Objective:

To determine whether spinal manipulative therapy (SMT) inhibits paraspinal motor unit action potentials (MUAPs) and whether thrust loading rate governs this response.

Summary of Background Data:

Intracapsular saline injection reduces paraspinal MUAPs evoked by annular disc stimulation, indicating a physiological mechanoreceptor-mediated reflex. Whether external mechanical thrusts elicit analogous inhibition, and whether thrust characteristics modulate it, is untested.

Materials and Methods:

Seven anesthetized pigs (45–60 kg) were instrumented with L4–L5 disc stimulation and bilateral multifidus EMG electrodes. Three SMT interventions were delivered to the left L4 facet joint: Sham (20 N, 5 ms), HVLA (200 N, 100 ms), and impulsive (200 N, ∼2 ms). Disc-evoked MUAPs were recorded over 30 minutes and analyzed using peak-to-peak and integrated EMG (iEMG) at 10 time points. The Wilcoxon and Friedman tests were used to compare interventions.

Results:

Peak-to-peak MUAP trough inhibition among impulsive responders was 46% (range: 25%–65%; P =0.016). Impulsive SMT produced ~20% iEMG inhibition versus Sham (0.92 vs . 1.12; P =0.016, d =−1.09), and sustained inhibition AUC was two-fold greater than Sham ( P =0.031) or HVLA ( P =0.047). The median frequency increased with the loading rate (93, 115, 153 Hz; Friedman P =0.018), and inhibition was lateralized ipsilateral to the SMT thrust side ( P =0.008; d =−1.98).

Conclusions:

High-loading-rate impulsive SMT produces lateralized mechanoreceptor-mediated paraspinal muscle inhibition identified by peak-to-peak amplitude analyses and more sensitive integrated and frequency-domain EMG measures.

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