Archive for category Biomechanical


To date, the diagnosis of whiplash injuries  has been very difficult and largely based on subjective, clinical  assessment. The work by Winters and Peles Multiple Muscle  Systems–Biomechanics and Movement Organization. Springer, New York  (1990) suggests that the use of finite helical axes (FHAs) in the neck  may provide an objective assessment tool for neck mobility. Thus, the  position of FHA describing head-trunk motion may allow discrimination  between normal and pathological cases such as decreased mobility in  particular cervical joints. For noisy, unsmoothed data, the FHAs must be  taken over rather than large angular intervals if the FHAs are to be  reconstructed with sufficient accuracy; in the Winters and Peles study,  these intervals were approximately 10 degrees.

In order to study the  movements’ microstructure, the present investigation uses instantaneous  helical axes (IHAs) estimated from low-pass smoothed video data. Here,  the small-step noise sensitivity of the FHA no longer applies, and  proper low-pass filtering allows estimation of the IHA even small  rotation velocity omega of the moving neck. For marker clusters mounted  on the head and trunk, technical system validation showed that the IHAs  direction dispersions were on the order of one degree, while their  position dispersions were on the order of 1 mm, for low-pass cut-off  frequencies of a few Hz (the dispersions were calculated from  omega-weighted errors, in order to account for the adverse effects of  vanishing omega).

Various simple, planar models relating the  instantaneous, 2-D centre of rotation with the geometry and kinematics  of a multi-joint neck model are derived, in order to gauge the utility  of the FHA and IHA approaches.

Some preliminary results on asymptomatic  and pathological subjects are provided, in terms of the ‘ruled surface’  formed by sampled IHAs and of their piercing points through the  mid-sagittal plane during a prescribed flexion-extension movement of the  neck.

J Biomechanics. 1994; 27(12):1415-32.

Author information: Woltring HJ, Long K, Osterbauer PJ, Fuhr AW.  Whiplash Analysis, Inc. Phoenix, AZ.

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To determine the biomechanical characteristics of five clinically common methods of cervical spine manipulation.


Descriptive study.


Human Performance Lab, University of Calgary.


Five volunteer practitioners treating symptomatic patients from their own clinical populations.


Five commonly used methods of cervical spine manipulation: lateral break (LAT), Gonstead (GON), Activator (ACT), toggle (TOG), rotation (ROT).


Mean thrust duration (msec), normalized mean peak force (N), slope (N/msec), force profile (graphic representation of the above values.


Outcome measures for each manipulative technique were as follows: LAT = normalized mean peak force of 102.2 N at 86.7 msec, GON = 109.8 N at 91.9 msec, ACT = 40.9 N at 31.8 msec, TOG = 117.6 N at 47.5 msec, ROT = 40.5 N at 79.1 msec.


The observed differences and similarities in force profiles between the five techniques studied here may partly be the manifestation of how a particular technique delivers force to the cervical spine. The clinical significance of force profile characterization is not yet known.

J Manipulative Physiol Ther. 1993 Nov-Dec;16(9):573-7. [PMID:8133191]

Author information: Kawchuk GN, Herzog W. University of Calgary, Faculty of Physical Education, Alberta, Canada.

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Background and Objectives:

Knowledge of spine  segment motion patterns or “kinematics” is of interest to understanding  the time-dependent or viscoelastic behavior of the spine, postural  kinematics, vibration response of the spine, and response of the spine  to chiropractic manipulations. The ability to quantify in vivo spine  segment “kinematics” is clinically significant in terms of both the  diagnosis and treatment of spinal disorders and LBP. The objectives of  this study were to a) study the relative motions of the normal and  abnormal lumbar spine in response to transverse (postero-anterior)  manipulative thrusts, and b) mathematically model the dynamic  viscoelastic behavior of the spine.


An intervertebral motion measuring device (IMD) was  used to quantify the in vivo Interspinous kinematic behavior of the  normal (1 volunteer) and unstable (2 patients with abnormal lumbar discs  consulting for spine surgery) human lumbar spine. The IMD is a spatial  linkage system capable of measurement of motion in the sagittal plane,  and was rigidly attached to the L2-L3 and L3-L4 spinous processes using  2.4 mm Steinmann pins. Rotation, translation and shear of the lumbar  vertebrae were obtained in response to transverse impulses from an  Activator adjusting instrument (AAI) applied to the spinous process of  adjacent segments of the thoraco-lumbar spine with the patients lying  prone. Impulse force and acceleration in transverse plane were measured  using a uniaxial load cell and accelerometer.


The impulses (= 100N peak, < 100 msec duration)  produced exponentially damped oscillations in the lumbar motion segment  with displacement amplitude peaks (axial=0.5-1.0 mm, shear = 0.1-0.3 mm,  rotation=0.5-1 degrees) located at frequencies ranging from 10-15 Hz.  Alterations in the propagation of the impulse stimulus were observed in  the two patients with disc pathology. The kinematic data is currently  being analyzed using a dynamic, three-parameter linear solid  viscoelastic model to obtain intrinsic properties of the: ‘spine (moduli  or stiffness and viscosity).


Although this study was conducted using  only a few human subjects, the preliminary results suggest that one may  be able to discriminate between normal and abnormal kinematic behavior  by measuring and analyzing the impulse response. of the spine in viva.  Such measurements may be used to evaluate the mechanical effectiveness  of various manipulative, surgical and rehabilitative procedures of the  spine.

Reference: T. Keller, PhD, M. Nathan, MS, and A. Kaigle,  MS Dept. of Mechanical Engr. University of Vermont. Burlington, VT and  Depts. of Orthopedics (Occupational Unit), Sahlgren Hospital, Goteborg,  Sweden. Proceedings of the FCER’s 1993 International Conference on Spinal  Manipulation. Montreal, Quebec, Canada, April 30-May 1: pp. 51-5.

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Background and Objectives:

Little is known  about the dynamics of spinal manipulation and mechanical force manually  assisted short lever adjustments in particular. The purpose of this  study is to quantify the biomechanical response to impulsive loads  applied over the cervical spine. A previous study had enabled us to  quantify the response for the lumbar spine. This would enable the  estimation of the internal motion and loading that occurs due to the  instrument delivered short lever chiropractic adjustment.


An anthropomorphic model of the human  body has been constructed for this study. The Activator Adjusting  Instrument, a product of Activator Methods Inc, (Phoenix, AZ), is used  to produce the impulsive loads. The elements of the model involve bones,  ligaments, intervertebral discs and muscles which are constructed from  composite materials that closely mimic the passive properties of the  physiological systems. The instrumentation includes displacement,  acceleration and pressure transducers. The sampling rate of the data was  1,o00 Hz and filtering of the data is done using software.


The anthropomorphic model has been  used in a previous study to study the dynamics of spinal manipulation in  the lumbar spine. It has been found to be a reasonable substitute for  the human spine, in terms of the mechanical responses to forces and/or  torques. The present study involved data collection in the cervical  spine at the levels of C1, C2, C5 and C6. Preliminary data analysis has  been done and the movement response to applied thrusts on the spine has  been done qualitatively and a quantitative analysis is expected to be  done on data in the near future.


Anthropomorphic modeling may prove useful  in understanding the dynamics of spinal manipulation, particularly when  integrated with computer modeling and in vivo studies. Acknowledgement: This study was funded by the National Institute of Chiropractic Research.

Reference: Sridhar Venkataraman, BS, Gary T. Yamaguchi,  PhD, Paul J. Osterbauer, OG, and Arlan W. Fuhr .DC, Arizona State  University, Tempe. AZ, The National Institute of Chiropractic Research,  Phoenix. AZ; Evaluating Mechanical Force Manually Assisted Short Lever  adjusting using an Anthropomorphic model; In: The proceedings of the  FCER’s 1993 International Conference on Spinal Manipulation, Montreal,  Quebec, Canada, April 30-May 1, Page 13.

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Chiropractic mechanical force, manually assisted short lever adjusting is a spinoff of the specific toggle recoil adjusting techniques, which were based on the original chiropractic subluxation theory propounded by Daniel David Palmer in 1895. This article reviews: a) the principles of the chiropractic subluxation complex from the standpoint of its historical origin and present-day scientific status; b) the purpose and objectives of specific spinal manipulative techniques; c) the use of mechanical adjusting instruments to effect a velocity/direction controlled adjustive thrust; and d) an assessment of scientific and clinical data relating to the biomechanical and neurological aspects of mechanical force, manually assisted short lever adjusting.


Prime sources were from the National Library of Medicine’s on-line Index Medicus database, the Chirolars Research Resource Retrieval database, the Chiropractic Research Abstract Collection and the Chiropractic Library Consortium’s reference works. Direct search of other nonindexed chiropractic sources was limited to those available in the collection of the National Institute of Chiropractic Research. Early information never documented by publication was obtained by written personal communication.


The principal author selected articles reporting data (as opposed to anecdotal reports) from conference proceedings and peer-reviewed journals.


Data quality was assessed based on experimental conditions such as sample size, study design and statistical analysis.


While mechanical force, manually assisted short lever adjusting seemingly is capable of beneficially altering the cause/effect relationship of spinal subluxations, more research in the nature of controlled clinical trials is needed to ascertain its benefits in the chiropractic treatment of specific conditions.


Basic research is needed in order to establish the scientific basis for the chiropractic subluxation syndrome regardless of the technique employed.

J Manipulative Physiol Ther. 1992 Jun;15(5):309-17. [PMID:1302464]

Author information: Osterbauer PJ, Fuhr AW, Hildebrandt RW. Activator Methods, Inc. Phoenix, AZ.

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The authors studied relative bone movements in response to manipulative light taps to the spine. Piezoelectric accelerometers attached to bone of an anesthetized dog measured transverse, X-Z plane, movements of L2-L3 adjacent vertebrae while percussion thrusts of an instrument used for manipulation made inputs three vertebrae above and five vertebrae below the L2-L3 joint interface. Small, relative 1-mm translations and 0.5 degree rotations occurred during the first 19 msec. When one set of accelerometers were stabilized on the skin surface, half of the skin-bone translation maxima erred less than 2%. However, skin translations averaged 77% (SD = 2%) of bone translations and skin rotations averaged 95% (SD = 26%) of bone rotations. The results suggest the possibility that, with further development, piezoelectric accelerometers can be a noninvasive tool to study dynamic, relative, bone movement.

J Manipulative Physiol Ther. 1989 Feb;12(1):26-37. [PMID:2926284]

Author information: Smith DB, Fuhr AW, Davis BP. Activator Methods, Inc., Phoenix, Arizona 85060-0317.

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The accuracy and reproducibility of an electronic system to measure the displacement of a spring-loaded chiropractic adjusting instrument was examined. The electronic system included a piezoelectric force transducer, piezoelectric accelerometer transducers and a digital oscilloscope. Accuracy was studied by comparing electronic measurements with the expansion allowed by the mechanically limiting expansion-control knob of the instrument. The results suggested improvements for future accuracy verification checks and detected accuracy within about 10% of the expansion of the commonly used expansion-control-knob revolutions. Preliminary experiments are presented to show application of the system to studies on thrusts into the spine. The impedance-head-equipped spring-loaded Activator chiropractic adjusting instrument had a low velocity when used on the patient and appeared to cause bone movement and a measurable EMG response.

J Manipulative Physiol Ther. 1986 Mar;9(1):15-21. [PMID: 3701223]

Author information: Fuhr AW, Smith DB. Activator Methods, Inc. Phoenix, AZ.

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The Activator® Adjusting Instrument is a hand-held device which can produce adjusting force. Four activator adjusting instruments were used to introduce a force into a measuring system. Surprisingly, the force decreased linearly after two or three revolutions of the adjustment knob. The adjustment knob allows greater anvil movement when the activator adjusting instrument produces a force. A model based on the physical mechanics of the Activator adjusting instrument was able to explain 88 percent of the force variation. Similar data was available from meric and DNFT adjusting so they were compared with the Activator adjusting instrument. The fixed energy of the activator adjusting instrument lead us to the hypothesis that significant movement of bone may not be necessary for the healing process to take place.

Dig Chiropr Econ 1984 (DEC); 27 (3): 17-19.

Author information: Duell ML.

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