Archive for category Biomechanical

Abstract

OBJECT:

Develop an analytical theory describing the dynamics of small impulses applied to vertebrae, such as in chiropractic adjustments or spinal manipulative therapy.

DESIGN:

Data were compared with damped harmonic oscillator models of vertebrae.

BACKGROUND:

Evidence accumulates that chiropractic adjustments are effective in addressing a variety of health problems. However, the biomechanics characterizing spinal manipulation is largely unknown. Recently, relative separations of the L2-L3 vertebrae subsequent to activator adjusting instrument thrusts were measured in vivo at 2048 Hz.

RESULTS:

Nine-parameter models for axial, shear and angular motions were fit to sets of 350 data points. They required frequencies of 5, 8 and 11 Hz, corresponding to well-known spinal resonances. The fits are excellent, with 0.75 < corrected R(2) < 0.96. Stiffnesses are calculated to be less than 10% of elastic zone values. Viscosities of the paravertebral medium are predicted to be between 6 and 30 poise, comparable to synovial fluids.

CONCLUSIONS:

This model ties together vertebral responses to small impulses with spinal resonances and other spinal/vertebral characteristics. Stiffness dominates damping resistance except in angular motions. Coupling appears unimportant in adjacent vertebral responses to small impulses. Further research is needed to clarify this issue.

RELEVANCE:

This study indicates how both force (determining amplitude) and thrust speed or duration (determining frequencies excited) may enter in terms of optimizing the efficacy of chiropractic adjustments. If stimulation of specific spinal frequencies, say as central nervous input, were most essential, then many chiropractic thrusts could be clinically similar. This may explain how over 90 chiropractic techniques can co-exist.


Clin Biomech (Bristol, Avon). 2000 Feb;15(2):87-94. [PMID:10627324]

Author information: Research Department, Life Chiropractic College West, 22336 Main St., Hayward, CA 94541, USA.

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Introduction:

Lumbar spinal disorders including radial  tears, disc degeneration, segmental instability and segmental  dysfunction have been considered common causes of persistent back pain  and sciatica. Such disorders may be characterized as exhibiting  alterations in the mechanical behavior to loading, notably, changes in  spinal stiffness. Studies investigating posteroanterior (PA) forces in  spinal stiffness assessment have shown relationships to spinal level,  body type, and lumbar extensor muscle activity. Such measures may be  important determinants to discriminate between patients with low back  pain and asymptomatic subjects. However, little objective evidence is  available discerning variations in PA stiffness, a more complete  assessment based upon dynamic stiffness measurements (driving-point  impedance) and concomitant neuromuscular response may offer more  information concerning mechanical properties of the low back, Thus, the  aim of the current study was to determine the stiffness and  neuromuscular characteristics of the asymptomatic and symptomatic low  back,

Methods:

This study is a prospective clinical study  investigating the mechanical and muscular behavior of lumbar spinal  segments to high loading rate PA forces, 22 subjects (12 male & 10  female, mean age of 42.8+ or – 17.5 years, range 15-73 years) underwent a  comprehensive physical examination consisting of history,  orthopedic/neurologic examination, lumbar range of motion, pressure  algometry and plain film radiographic exanimation of the lumbar spine. A  visual analog score (VAS), Oswestry Low Back Disability Index, and  Health Status Questionnaire (SF-36) were obtained for all subjects and  categorization was made on the basis of symptom frequency, as well as  positive vs. negative orthopedic exam, acute vs. chronic (>12 weeks)  low back pain (LBP) history and electromyography (EMG) response to PA  mechanical stimulation. Each subject was placed in the prone position by  use of a motorized vertical/horizontal table. Surface, linear  enveloped, EMG recordings were obtained from electrodes (8 lead s)  located over the L3 and L5 paraspinal musculature to monitor the  bilateral neuromuscular activity of the erector spinae group during the  PA stiffness measurement protocol, Prior to and immediately following  the PA mechanical stimulation, each subject performed three consecutive  maximal effort isometric trunk extensions to normalize EMG data. A  hand-held Activator II Adjusting Instrument equipped with a load cell  and accelerometer was used to deliver high rate (<0.1 msec ) PA  mechanical stimulation (450 N) to several common spinal landmarks  including the PSIS, sacral base and L5, L4, L2, T12, T8 spinous and  transverse processes. Driving point impedance (Z, Ns/m) was calculated  for each of the thrusts, from which the effective dynamic stiffness (Z x  2(3.21)f) was determined.

Results:

Two of the subjects were asymptomatic (no prior history of LBP), 6 had occasional LBP symptoms, 4 intermittent, and 10 had chronic symptoms of LBP. Subjects with chronic symptoms were characterized by higher effective dynamic stiffness at all levels and had a 2.5-fold higher Oswestry index and VAS score in comparison to the other subjects. Ten of the subjects had an abnormal orthopedic examination and were characterized by a significantly higher dynamic stiffness at all levels. These ten subjects also had over a 2.5-fold greater Oswestry index and VAS score in comparison to the subjects with a normal exam. LBP chronicity was also associated with a 2.5-fold and 3~fold greater Oswestry and VAS score, respectively, in comparison to acute pain sufferers. no differences in dynamic stiffness were observed between these subject groups, however. Of interest was our finding that 16 of the subjects exhibited a hyper-neuromuscular response in response to the PA mechanical stimulation. A hyper-neuromuscular response was characterized as a prominent EMG response (≥ 10% of the isometric extension EMG response) in 10% or more of the EMG recordings (80 total/subject). In this group of subjects the Oswestry index and VAS score were nearly 3-fold and 6-fold greater, respectively, in comparison to subjects which showed little or no mechanically-activated EMG response. Also noteworthy, was the finding that, while lumbar level PA stiffness measurements were similar for these two groups, the thoracic level PA stiffness values were significantly greater in the hyper-neuromuscular group.

Discussion:

The results of this preliminary study provide additional support for clinical assessment strategies that utilize a non-invasive dynamic stiffness measurement system to probe and quantify the mechanical characteristics of the spine. It was noted that subjects with hyper-neuromuscular responses presented with more severe disability outcome scores and a positive orthopedic exam. Further measurements of the dynamic stiffness and neuromuscular characteristics of the symptomatic and asymptomatic LBP population are required to clarify the significance of this observation. Such diagnostic measurements, when combined with conservative manipulative care of the back may prove to be a particularly effective means to diagnostically probe and treat lower back disorders.


Reference: Christopher J. Colloca, D.C., Tony S. Keller,  Ph.D. , Arlan W. Fuhr, D.C.; Muscular And Mechanical Behavior Of The  Lumbar Spine In Response To Dynamic Posteroanterior Forces; Proceedings  of the 26th Annual Meeting of the International Society for the Study of  the Lumbar Spine, Kona, Hawaii. Toronto: ISSLS, 1999: 136A.

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Abstract

OBJECTIVE:

To determine the dynamic force-time and force-frequency characteristics of the Activator Adjusting Instrument and to validate its effectiveness as a mechanical impedance measurement device; in addition, to refine or optimize the force-frequency characteristics of the Activator Adjusting Instrument to provide enhanced dynamic structural measurement reliability and accuracy.

METHODS:

An idealized test structure consisting of a rectangular steel beam with a static stiffness similar to that of the human thoracolumbar spine was used for validation of a method to determine the dynamic mechanical response of the spine. The Activator Adjusting Instrument equipped with a load cell and accelerometer was used to measure forces and accelerations during mechanical excitation of the steel beam. Driving point and transfer mechanical impedance and resonant frequency of the beam were determined by use of a frequency spectrum analysis for different force settings, stylus masses, and stylus tips. Results were compared with beam theory and transfer impedance measurements obtained by use of a commercial electronic PCB impact hammer.

RESULTS:

The Activator Adjusting Instrument imparted a very complex dynamic impact comprising an initial high force (116 to 140 N), short duration pulse (<0.1 ms) followed by several lower force (30 to 100 N), longer duration impulses (1 to 5 ms). The force profile was highly reproducible in terms of the peak impulse forces delivered to the beam structure (<8% variance). Spectrum analysis of the Activator Adjusting Instrument impulse indicated that the Activator Adjusting Instrument has a variable force spectrum and delivers its peak energy at a frequency of 20 Hz. Added masses and different durometer stylus tips had very little influence on the Activator Adjusting Instrument force spectrum. The resonant frequency of the beam was accurately predicted by both the Activator Adjusting Instrument and electronic PCB impact hammer, but variations in the magnitude of the driving point impedance at the resonant frequency were high (67%) compared with the transfer impedance measurements obtained with the electronic PCB impact hammer, which had a more uniform force spectrum and was more repeatable (<10% variation). The addition of a preload-control frame to the Activator Adjusting Instrument improved the characteristics of the force frequency spectrum and repeatability of the driving point impedance measurements.

CONCLUSION:

These findings indicate that the Activator Adjusting Instrument combined with an integral load cell and accelerometer was able to obtain an accurate description of a steel beam with readily identifiable geometric and dynamic mechanical properties. These findings support the rationale for using the device to assess the dynamic mechanical behavior of the vertebral column. Such information would be useful for SMT and may ultimately be used to evaluate the [corrected] biomechanical effectiveness of various manipulative, surgical, and rehabilitative spinal procedures.


J Manipulative Physiol Ther. 1999 Feb;22(2):75-86. [PMID:10073622]

Author information: Keller TS, Colloca CJ, Fuhr AW. Department of Mechanical Engineering, University of Vermont, Burlington, USA.

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Abstract

OBJECTIVE:

The purpose of this study was to measure the relative movements of vertebrae during manipulative thrusts to unembalmed post-rigor mortis human cadavers.

SETTING:

The investigation was conducted in the gross anatomy laboratory at the University of Calgary.

SUBJECTS:

Two 77-yr-old, unembalmed, post-rigor mortis, male cadavers were used.

INTERVENTIONS:

The movements of vertebrae were investigated by using high-speed cinematography to record the movements of bone pins threaded into T10, T11 and T12 during spinal manipulative therapy to unembalmed post-rigor human cadavers. A single clinician delivered a series of posterior-to-anterior (p-to-a) thrusts to the right transverse process of either T10, T11 or T12, using a reinforced hypothenar contact. Relative p-to-a and lateral translations, as well as axial and sagittal rotations, in T10-T11 and T11-T12 were calculated. Corresponding p-to-a forces exerted by the clinician onto the cadaver were recorded using a pressure pad.

MAIN RESULTS:

Significant relative movements were measured primarily between the targeted and immediately adjacent vertebrae during the thrusts. Vertebral pairs remained slightly ‘hyper-extended’ after the rapid thrusts to T11, when the p-to-a forces returned to preload levels.

CONCLUSIONS:

These findings may be useful for the understanding of the deformation behavior of the vertebral column during therapeutic manipulation. A fully three-dimensional analysis of all six degrees of freedom, using a larger number of unembalmed cadavers, would be useful in clarifying the relationship between the externally applied forces and the observed relative movement patterns of the vertebrae.


J Manipulative Physiol Ther. 1997 Jan;20(1):30-40. [PMID:9004120]

Author information: Gál J, Herzog W, Kawchuk G, Conway PJ, Zhang YT. Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Alberta, Canada.

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Excerpt:

Chapter 22 | Activator Methods Chiropractic Technique (Mosby)

The prevalence and economic impact of acute  and chronic back pain (BP) and the understanding that many BP problems  have mechanical origins have prompted clinicians and researchers to the  search for improved analytic and experimental methods to quantify the  biomechanical characteristics of the normal and abnormal human spine.  This chapter provides a brief review of the biomechanics of spinal  manipulation, which is followed by a detailed summary of the dynamic  response of the human spine to the Activator Method of chiropractic  posterior anterior (PA) manipulation.

Basic Spine Biomechanics: The spinal column combines an  intricate architectural arrangement of bone, muscle, and soft tissue  components to form a structure of mechanical as well as physiologic  significance. Not only does the spinal column serve to protect the  spinal cord but it also transmits, attenuates, and distributes the  static (time-invarying) and dynamic (time-varying) forces associated  with daily activities. Although the spinal column provides the  structures for load transmission and attenuation, the pathways for load  transmission and attenuation may be greatly altered during voluntary  (postural changes) and involuntary (fatigue) activities, producing  unstable and pathologic changes to the kinematic behavior of the spinal  column. 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 low back pain (LBP).2° The ability  to quantify in vivo spine segment motion or kinematics, tog ether with  the concomitant forces or kinetics, is therefore, of clinical  significance in terms of both diagnosis and treatment of spinal  disorders and back pain.


Reference: Keller TS. Engineering – in vivo transient  vibration analysis of the normal human spine. Section VIII, Chapter 22, pp 431-450, in Fuhr AW,  Green JR, Collaca CJ, Keller TS. Activator Methods Chiropractic  Technique textbook, St. Louis: Mosby, 1997.

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Abstract

OBJECTIVE:

To create a statistical model using three-dimensional (3D) head kinematics and range of motion (ROM) to distinguish between people with whiplash syndrome and asymptomatic controls.

STUDY DESIGN:

Cross-sectional study to estimate validity of diagnostic measures.

METHODS:

Fifty-one asymptomatic controls (most of whom were women), 18-35 yr old and 30 matched whiplash trauma patients seeking care from suburban outpatient clinics were sought. 3D kinematic parameters of head motion were obtained during tracking tasks (e.g., flexion, extension, etc.) and cervical ROM was measured via a head mounted inclinometer. Their level of pain and disability was assessed via a self-administered neck disability index questionnaire and visual analog pain scale (VAS).

RESULTS:

A scoring system of biomechanical abnormalities derived from the vertical piercing point, its second derivative and symmetry during oblique tasks. The scores ranged from a minimum of 0 to a maximum of 3. A cutoff of > or = 0.5 correctly identified the greatest number of subjects and minimized false positives (sensitivity 77%, specificity 82%, likelihood ratio 4.5). ROM performed similarly well at a cutoff of 1 SD below the normative mean (sensitivity 77%, specificity 84%, likelihood ratio 3.9).

CONCLUSIONS:

There is potential for biomechanical analysis to objectively detect abnormalities. The statistical model yielded moderate to high sensitivity and specificity using 3D helical-axis parameters of the head and standard ROM. The model development will continue via this process in future studies. These data could be a first step toward the creation of useful, noninvasive protocols for the diagnosis and management of soft tissue trauma of the neck.


J Manipulative Physiol Ther. 1996 May;19(4):231-7. [PMID:8734397]

Author information: Osterbauer PJ, Long K, Ribaudo TA, Petermann EA, Fuhr AW, Bigos SJ, Yamaguchi GT. Gait Laboratory, Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Boston, MA, USA.

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Abstract

OBJECTIVE:

To determine the general nature of the biomechanical response of the vertebrae to small forces, such as spinal manipulative therapy (SMT).

DESIGN:

Perturbation theoretical methods of physics and mechanical energy considerations are used to derive the equations of motion of the vertebral bodies moving under the combined influences of ligamentous and discogenic forces, applied forces and dissipative forces attributable to surrounding tissues.

RESULTS:

The allowable solutions to the equations of motion determine that the mechanical response of any vertebra to SMT should consist of a superposition of damped oscillations. This is based on the most general assumptions about the spine that are consistent with clinical observations, namely, that patients can lie stably motionless, and is independent of the specifics of any spinal model.

DISCUSSION:

The extant data are shown to be consistent with this theory. The implications for future research and clinical practice are explored.

CONCLUSIONS:

Vertebral motion in response to SMT seems to occur in two distinct phases: an initial, (passive) oscillatory response to the SMT thrust, governed by ligamentous and discogenic forces, and a later, less regular motion, probably caused by muscular reflex contractions. Evidence of this includes direct measurement of oscillations, surface electromyogram measurements of muscle responses and detection of multiple spinal resonances. Further research on the muscular reflex responses to SMT is necessary. Most SMT should initiate some of the normal-mode oscillations of the vertebrae. There may be up to 144 different frequencies of vertebral oscillatory motion in each individual in any posture; those frequencies detected thus far are consistent with the predicted relationship between frequencies, vertebral body masses and coefficients of stiffness. Further data are needed to confirm the detailed validity of this theory.


J Manipulative Physiol Ther. 1996 May;19(4):238-43. [PMID:8734398]

Author information: Solinger AB. Research Department, Life Chiropractic College-West, San Lorenzo, CA, USA.

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Abstract

STUDY DESIGN:

Task-specific and subject-specific lumbar trunk muscle function, muscle geometry, and vertebral density data were collected from 16 men. A biomechanical model was used to determine muscle strength and the compressive forces acting on the lumbar spine.

OBJECTIVES:

To develop an anatomic biomechanical model of the low back that could be used to derive task-specific muscle function parameters and to predict compressive forces acting on the low back. Several model-specific constraints were examined, including the notion of bilateral trunk muscle anatomic symmetry, the influence of muscle lines of action, and the use of density-derived vertebral strength for model validation.

SUMMARY OF BACKGROUND DATA:

Clinical and basic science investigators are currently using a battery of diverse biomechanical techniques to evaluate trunk muscle strength. Noteworthy is the large variability in muscle function parameters reported for different subjects and for different tasks. This information is used to calculate forces and moments acting on the low back, but limited data exist concerning the assessment of subject-specific, multiaxis, isometric trunk muscle functions.

METHODS:

A trunk dynamometer was used to measure maximum upright, isometric trunk moments in the sagittal (extension, flexion) and coronal (lateral flexion) planes. Task- and subject-specific trunk muscle strength or “gain” was determined from the measured trunk moments and magnetic resonance image-based muscle cross-sectional geometry. Model-predicted compressive forces obtained using muscle force and body force equilibrium equations were compared with density-derived estimates of compressive strength.

RESULTS:

Individual task-specific muscle gain values differed significantly between subjects and between each of the tasks they performed (extension > flexion > lateral flexion). Significant differences were found between left side and right side muscle areas, and the lines of action of the muscles deviated significantly from the vertical plane. Model-predicted lumbar compressive forces were 38% (lateral flexion) to 73% (extension) lower that the L3 vertebral compressive strength estimated from vertebral density.

CONCLUSION:

The present study suggests that biomechanical models of the low back should be based on task-specific and subject-specific muscle function and precise geometry. Vertebral strength estimates based upon vertebral density appear to be useful for validation of model force predictions.


Spine (Phila Pa 1976). 1996 Feb 15;21(4):427-33. [PMID:8658245]

Author information: Gzik DC, Keller TS, Szpalski M, Park JH, Spengler DM. Department of Mechanical Engineering, University of Vermont, Burlington, USA.

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Abstract

OBJECTIVES:

To (i) measure lumbar intervertebral motion patterns produced during low force, high frequency posteroanterior (PA) thrusts applied to adjacent thoracolumbar spinal segments; (ii) determine the dependence of PA stiffness and impedance characteristics of the thoracolumbar spine on loading frequency; and (iii) ascertain the feasibility of using PA stiffness or impedance to characterize the in vivo mechanical response of the spine during spinal manipulation.

SETTING:

Hospital in Gothenburg, Sweden.

SUBJECTS:

Three subjects–one normal (male), one patient diagnosed with L4-5 degenerative disk disease (female), and one patient diagnosed with L5 retrospondylolisthesis (male).

INTERVENTIONS:

Intervertebral motion device (IMD) attached to pins inserted into the L3-4 or L4-5 spinous processes. Four repeated PA impulses were delivered to each of the spinous processes (T11-L3) using an Activator Adjusting Instrument with a force-acceleration measurement system.

OUTCOME MEASURES:

Peak-to-peak intervertebral axial displacement, PA shear displacement and flexion-extension (FE) rotation were obtained using the IMD. Thoracolumbar PA impedance (force/velocity) vs. frequency histories and peak PA dynamic stiffness (impedance x frequency) were determined from the force-acceleration measurements. Averages and standard deviations of these measures were calculated from the repeated interventions performed at each level.

MAIN RESULTS:

For the normal subject, the AAI PA impulses applied to the L2 spinous process (72 +/- 9 N) produced a 1.62 +/- 1.06 mm peak-to-peak intervertebral axial displacement, 0.48 +/- 0.1 mm PA shear displacement, and 0.89 +/- 0.49 degrees FE rotation at the L3-4 spinal segment. The amplitude of the lumbar intervertebral motion in the normal subject’s spine decreased approximately sixfold when the AAI impulses were delivered further from the IMD measurement site. In both patients the axial, PA shear and FE lumbar intervertebral motions were of the same magnitude, but showed less variability than the normal subject as the AAI impulses were delivered closer to the IMD measurement site. The normal thoracolumbar spine exhibited a maximum dynamic PA impedance at a frequency of approximately 100-150 Hz, resulting in a peak PA stiffness ranging from 62 KN/m (L2 segment) to 124 KN/m (T11 segment). Thoracolumbar PA stiffness values tended to be higher for the patient with a severely degenerated disk (85-362 KN/m), whereas the patient with retrospondylolisthesis had a lower PA stiffness (32-96 KN/m).

CONCLUSIONS:

In vivo kinematic measurements of the normal and pathologic human lumbar spine indicate that low force, PA impulses produce measurable segmental motions and reinforce the notion that mechanical processes play an important role in spinal manipulation and mobilization. Calculations of the peak dynamic stiffness derived from impedance vs. frequency measurements indicate that the dynamic stiffness of the thoracolumbar spine is considerably greater than previously reported stiffness values obtained using static and quasistatic manipulation and mobilization procedures. Computations of spinal input impedance are relatively simple to perform, can provide a noninvasive measure of the dynamic mechanical behavior of the spine, appear to have potential to discriminate pathologic changes to the spine, and warrant further study on a larger sample of normals and patients. Ultimately, chiropractic clinicians may be able to use low force, impact type spinal manipulation, together with dynamic impedance analysis procedures, to quantify the mechanical response of the normal and abnormal spine, to perform spinal diagnosis and subsequently to prescribe therapeutic treatment to patients.


J Manipulative Physiol Ther. 1994 Sep;17(7):431-41. [PMID: 7989876]

Author information: Nathan M, Keller TS. Department of Mechanical Engineering, University of Vermont, Burlington 05405-0156.

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Subject: The Activator Adjusting Instrument – Biomechanical

 

Reference: Tony S. Keller;  J.B. Lehneman…Musculoskeletal Research Lab, February 1994: pp.1-16

 

Introduction: The Activator Adjusting Instrument  (AAI) is a devise used for chiropractic manipulations. The device is  intended to produce repeatable impacts (manipulations) at various force  settings. The force is easily adjusted by turning the small knob on the  lower part of the device.

 

Objective: The purpose of this study is to determine  the effect of the force setting, and preload on the actual force  delivered by the AAi to the impact surface.

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