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Neural Response During a Mechanically Assisted Spinal Manipulation in an Animal Model

Neural Response During a Mechanically Assisted Spinal Manipulation in an Animal Model: A Pilot Study

The Chiro.Org Blog

SOURCE:   J Nov Physiother Phys Rehabil. 2015 (Sep);   2 (2):   20–27 ~ FULL TEXT

William R. Reed, DC, PhD,
Michael A.K. Liebschner, PhD,
Randall S. Sozio, BS, LATG,
Joel G. Pickar, DC, PhD,
Maruti R. Gudavalli, PhD

Palmer Center for Chiropractic Research,
Davenport, IA, USA.

INTRODUCTION:   Mechanoreceptor stimulation is theorized to contribute to the therapeutic efficacy of spinal manipulation. Use of mechanically-assisted spinal manipulation (MA-SM) devices is increasing among manual therapy clinicians worldwide. The purpose of this pilot study is to determine the feasibility of recording in vivo muscle spindle responses during a MA-SM in an intervertebral fixated animal model.

METHODS:   Intervertebral fixation was created by inserting facet screws through the left L5-6 and L6-7 facet joints of a cat spine. Three L6muscle spindle afferents with receptive fields in back muscles were isolated. Recordings were made during MA-SM thrusts delivered to the L7 spinous process using an instrumented Activator IV clinical device.

RESULTS:   Nine MA-SM thrusts were delivered with peak forces ranging from 68-122N and with thrust durations of less than 5ms. High frequency muscle spindle discharge occurred during MA-SM. Following the MA-SM, muscle spindle responses included returning to pre-manipulation levels, slightly decreasing for a short window of time, and greatly decreasing for more than 40s.

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Instrument Adjusting
a.k.a. Mechanically-assisted Adjustments

CONCLUSION:   This study demonstrates that recording in vivo muscle spindle response using clinical MA-SM devices in an animal model is feasible. Extremely short duration MA-SM thrusts (<5ms) can have an immediate and/or a prolonged (> 40s) effect on muscle spindle discharge. Greater peak forces during MA-SM thrusts may not necessarily yield greater muscle spindle responses. Determining peripheral response during and following spinal manipulation may be an important step in optimizing its’ clinical efficacy. Future studies may investigate the effect of thrust dosage and magnitude.

KEYWORDS:   Cat; Manual therapy; Muscle spindle; Neurons afferent; Neurophysiology; Spinal fixation; Spinal manipulation; Zygapophyseal joint

From the Full-Text Article:


Spinal manipulation is a form of manual therapy commonly used by clinicians and therapists for conservative treatment of musculoskeletal complaints. Spinal manipulation is typically distinguished from spinal mobilization by the presence of a short duration mechanical thrust applied to the spinal column using either direct hand contact (≤150ms) or one of several commercially available mechanical devices (≤10ms) [1-4]. Among chiropractic clinicians, use of mechanically-assisted spinal manipulation (MA-SM) is growing rapidly with reports that 40-60% of practitioners in the United States, Britain, Belgium, Canada, Australia, and New Zealand use MA-SM in some capacity of patient care [5-10].

Spinal manipulation has been shown to be effective in the treatment of neck and low back pain and is recommended by clinical guidelines and evidence reports [11-16]. Several reviews regarding the clinical efficacy, safety, usage, and mechanical effects of MA-SM have recently been published [17-20]. A majority of the MA-SM reviews have noted study weaknesses such as small sample size, non-randomization, and/or lack of a placebo or control group. Despite these limitations, great strides have recently been made in determining the mechanical characteristics and/or biological effects of MA-SM [1-4, 21-31]. These studies may provide a foundation for larger randomly controlled trials of MA-SM therapy. One distinct advantage MA-SM offers over manually delivered manipulative thrusts in a research setting is that the thrust velocity and thrust magnitude can be standardized. This feature is of particular importance in efficacy and mechanistic studies investigating the biomechanical and/or neurophysiological effects of spinal manipulation. In addition, MA-SM devices can be mechanically altered to provide an adequate sham spinal manipulation (no force delivered) which is more difficult to accomplish with manually delivered manipulative thrusts.

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