The Impulsive Adjustment: State-of-the-Art Technology Enables Spine Monitoring Simultaneously During Treatment

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 Christopher J. Colloca, D.C.

CEO and Founder of Neuromechanical Innovations

A ISO 13485 Certified Medical Device manufacturer of the Impulse® family of adjusting instruments, based in Chandler, Arizona.

Prominent Spine Researcher and Reviewer

He can be reached at DrC100@aol.com or at www.neuromechanical.com

INTRODUCTION

            Inherent in the definition of chiropractic adjustment is the need to identify abnormal mobility and/or alignment and the introduction of specifically applied forces intended to reduce or correct the dysfunction.  Inasmuch, over a decade ago, I placed my research focus into developing technology geared towards  the ability to quantify spinal displacements and monitor spinal motion responses during chiropractic adjustments.  With this agenda, I assembled an international research team to examine the biomechanical characteristics of various spinal pathologies and their relationship to spinal motion. Born out of this research was a validated non-invasive spinal stiffness assessment methodology that compared our methods to a gold-standard intersegmental motion technique that we published in 2009 in the journal, Spine (Colloca et al. 2009). Forces that are relatively large in magnitude, but act for a very short time (much less than the natural period of oscillation), are called impulsive.

Quantifying Spinal Pathology

Segmental instability and pathology of the spine are believed to produce abnormal patterns of motion and forces, which may play a significant role in the etiology of musculoskeletal disorders (Nachemson 1985).  The ability to quantify in vivo spine segment motion (displacement) and stiffness (force/deformation) in response to forces is thus considered to be of clinical significance in terms of both diagnosis and treatment of spinal disorders. Moreover, knowledge of spine segment motion patterns, forces and stiffness is also of fundamental interest to understanding the postural, time-dependent and dynamic response of the spine, the role of spinal implants in mechanical load sharing, and the response of the extremities (appendicular skeleton) and spine (axial skeleton) to externally applied forces such as chiropractic adjustments (Keller et al. 2002).    

            The mechanical and physiologic response of the spine to PA forces is dependent upon many factors, including the intensity, direction, duration and frequency of the applied force. Of these factors, the frequency-response and frequency-dependent stiffness characteristics of the spine to PA dynamic loading is perhaps the least well understood. The dynamic PA frequency-dependent stiffness behavior of the human spine reflects the fact that the spine is a viscoelastic structure, albeit generally more elastic than viscous.  Different structures (ligaments, cartilage, bone, tendons, muscle) will exhibit varying degrees of time-dependent and frequency-dependent viscoelastic behavior.  Consequently, the overall structural/vibration response of the spine is modulated by both the architecture or structural organization of component tissues as well as load sharing provided by adjacent structures (e.g. rib cage, sternum, pelvis).  When such factors are combined with other considerations such as spinal curvature, the net effect is a complex structure-frequency-dependent mechanical behavior.

Structural Frequency Response Functions

            The general approach for determining the dynamic response of a man-made or biologic structure consists of simultaneously measuring an excitation or input signal (typically force) and response or output signal (displacement, velocity or acceleration) in the time domain and analyzing them in the frequency domain.  Two principal types of frequency response transfer functions can be determined: a ratio of like parameters such as the ratio of the force transmitted to the disturbing force (transmissibility), or a ratio of two dissimilar parameters such as the ratio of the disturbing force to the velocity transmitted (mechanical impedance). Frequency response functions, together with identification of the resonant frequencies associated with the vibration, provide important information concerning the mechanical behavior of the structure.  For example, when the spine is dynamically loaded along the PA direction a lower impedance value implies that the intervertebral joints are easier to excite and capable of greater mobility and storage of larger amounts of energy, whereas the opposite holds for transmissibility (Kazarian 1972).  A variety of mechanical vibration “transfer functions” can be defined for various excitation (input) and response (output) signals (Table 1).

Table 1. Dynamic Frequency Response Transfer Functions

Name	Transfer Function
Accelerance	acceleration/force (kg-1)
Effective Mass	force/acceleration (kg)
Mobility	velocity/force (m/Ns)
Impedance	force/velocity (Ns/m)
Compliance	deformation/force (m/N)
Stiffness	force/deformation (N/m)

            A very fast and efficient method to determine the broadband dynamic mechanical response of a structure is to use transient testing techniques such as impact testing. During impact testing, a hand-held instrument (typically a hammer) with a load cell mounted to it is used to deliver a force impulse to the structure, and the motion response is measured using an accelerometer either mounted to the structure or mounted directly to the instrument (driving-point). It is this technique that we have refined and patented for our unique approach of simultaneously monitoring spinal motions during chiropractic adjustments. In the next issue of the Journal, we will review the benefits of adjusting at the resonant frequency of the spine.

References

1. Colloca, C.J., Keller, T.S., Moore, R.J., Harrison, D.E., & Gunzburg, R. 2009. Validation of a noninvasive dynamic spinal stiffness assessment methodology in an animal model of intervertebral disc degeneration. Spine 2009, 34, (18) 1900-05.
2. Kazarian, L.E. 1972. Dynamic response characteristics of the human vertebral column. Acta Orthop Scand., Suppl 146, 1-186
3. Keller, T.S., Colloca, C.J., & Beliveau, J.G. 2002. Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization. Clin Biomech, 17, (3) 185-196
4. Nachemson, A. 1985. Lumbar spine instability. A critical update and symposium summary. Spine, 10, (3) 290-291