Archive for category Biomechanical

Abstract

OBJECTIVE:

The objectives of this study were to determine the ability of several commercial shockwave devices to achieve a desired thrust profile in a benchtop setting, determine the thrust profile in a clinical analog, and determine the influence of operator experience level on device performance.

INTERVENTION AND OUTCOME:

We conducted two different types of testing: (1) bench testing to evaluate the devices themselves, and (2) clinical equivalent testing to determine the influence of the operator.

CONCLUSIONS:

The results indicated a significant dependence of thrust output on the compliance of the test media. The Activator V-E device matched the ideal half-sine thrust profile to 94%, followed by the Impulse device (84%), the Activator IV/FS (74%), and the Activator II (48%). While most devices deviated from the ideal profile on the return path, the Impulse device exhibited a secondary peak. Moreover, the Activator V-E device provided evidence that the device performs consistently despite operator experience level.This has been a major concern in manual spinal manipulation. Based on our results, a hyper-flexible spine would receive a lower peak thrust force than a hypo-flexible spine at the same power setting. Furthermore, a hand-held operation further reduced the peak thrust force as it increased the system compliance. However, that influence was dissimilar for the different devices. Although controlled clinical trials are needed to determine the correlation between thrust profile and clinical outcome, already ongoing clinical studies indicate an improved patient satisfaction due to reduced treatment pain when devices are used with a thrust characteristic closer to an ideal sine wave.


Annals of Biomedical Engineering, Vol. 42, No. 12, December 2014 ( 2014) pp. 2524–2536 DOI: 10.1007/s10439-014-1115-4

Author information: Liebschner, Michael A. K.; Chun, Kwonsoo; Kim, Namhoon; and Ehni, Bruce

Department of Neurosurgery, Baylor College of Medicine, Houston, TX, USA; Research Service Line, Michael E. DeBakey VA Medical Center, Houston, TX, USA;  Exponent Failure Analysis, Houston, TX, USA;  Department of Pediatrics Cardiology, Baylor College of Medicine, Houston, TX, USA; and Neurosurgery Service Line, Michael E. DeBakey VA Medical Center, Houston, TX, USA

In Vitro Biomechanical Evaluation of Single Impulse and Repetitive

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Abstract

OBJECTIVE:

The goal of this study was to compare the variation of manipulative forces produced by instruments and a manual technique.

METHODS:

Four operators (2 experts and 2 novices) used 4 different mechanical instruments to apply force to a uniaxial load cell. A different group of 2 expert and 2 novice operators used a traditional manual technique to apply force to a sensor mat. Two primary outcome variables were obtained from each sensor system: peak-to-peak force magnitude (N) and peak-to-peak force duration (millisecond). Multiple analyses were performed to determine the absolute differences and variation in each variable.

RESULTS:

Force-producing instrumentation exhibited less variation in absolute force and force duration compared to manual techniques. However, the same instrument in the hands of different operators often produced significantly different values of absolute force and force duration. Although absolute values of force magnitude generally differed between operators, intraoperator variation was equal for instruments and the manual technique. Conversely, for force duration, significant differences in interoperator variability were observed for the manual technique and for one of the instruments.

CONCLUSIONS:

Force-producing instruments reduce absolute variation in force magnitude and duration. However, this reduction does not eliminate significant differences in absolute force parameters observed to occur between some operators using the same instrument. Given these observations, claims of instrument superiority that do not account for interoperator variability should be considered with caution.


J Manipulative Physiol Ther. 2006 Oct;29(8):611-8. [PMID:17045094]

Author information: Kawchuk GN, Prasad NG, McLeod RC, Liddle T, Li T, Zhu Q. University of Alberta, Edmonton, Canada.

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Abstract

OBJECTIVE:

The aim of this study was to quantify and compare the 3-dimensional intersegmental motion responses produced by 3 commonly used chiropractic adjusting instruments.

METHODS:

Six adolescent Merino sheep were examined at the Institute for Medical and Veterinary Science, Adelaide, Australia. In all animals, triaxial accelerometers were attached to intraosseous pins rigidly fixed to the L1 and L2 spinous processes under fluoroscopic guidance. Three handheld mechanical force chiropractic adjusting instruments (Chiropractic Adjusting Tool [CAT], Activator Adjusting Instrument IV [Activator IV], and the Impulse Adjusting Instrument [Impulse]) were used to randomly apply posteroanterior (PA) spinal manipulative thrusts to the spinous process of T12. Three force settings (low, medium, and high) and a fourth setting (Activator IV only) were applied in a randomized repeated measures design. Acceleration responses in adjacent segments (L1 and L2) were recorded at 5 kHz. The multiaxial intersegmental (L1-L2) acceleration and displacement response at each force setting was computed and compared among the 3 devices using a repeated measures analysis of variance (alpha = .05).

RESULTS:

For all devices, intersegmental motion responses were greatest for axial, followed by PA and medial-lateral (ML) measurement axes for the data examined. Displacements ranged from 0.11 mm (ML axis, Activator IV low setting) to 1.76 mm (PA axis, Impulse high setting). Compared with the mechanical (spring) adjusting instruments (CAT, Activator IV), the electromechanical Impulse produced the most linear increase in both force and intersegmental motion response and resulted in the greatest acceleration and displacement responses (high setting). Significantly larger magnitude intersegmental motion responses were observed for Activator IV vs CAT at the medium and high settings (P < .05). Significantly larger-magnitude PA intersegmental acceleration and displacement responses were consistently observed for Impulse compared with Activator IV and CAT for the high force setting (P < .05).

CONCLUSIONS:

Larger-magnitude, 3D intersegmental displacement and acceleration responses were observed for spinal manipulative thrusts delivered with Impulse at most force settings and always at the high force setting. Our results indicate that the force-time characteristics of impulsive-type adjusting instruments significantly affects spinal motion and suggests that instruments can and should be tuned to provide optimal force delivery.


J Manipulative Physiol Ther. 2006 Jul-Aug;29(6):425-36. [PMID:16904488]

Author information: Keller TS, Colloca CJ, Moore RJ, Gunzburg R, Harrison DE, Harrison DD. Musculoskeletal Research Foundation, Florida Orthopaedic Institute, Temple Terrace, Fla., USA.

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Abstract

Clinical reports and research studies have documented the behavior of chronic low back and neck pain patients. A few hypotheses have attempted to explain these varied clinical and research findings. A new hypothesis, based upon the concept that subfailure injuries of ligaments (spinal ligaments, disc annulus and facet capsules) may cause chronic back pain due to muscle control dysfunction, is presented. The hypothesis has the following sequential steps. Single trauma or cumulative microtrauma causes subfailure injuries of the ligaments and embedded mechanoreceptors. The injured mechanoreceptors generate corrupted transducer signals, which lead to corrupted muscle response pattern produced by the neuromuscular control unit. Muscle coordination and individual muscle force characteristics, i.e. onset, magnitude, and shut-off, are disrupted. This results in abnormal stresses and strains in the ligaments, mechanoreceptors and muscles, and excessive loading of the facet joints. Due to inherently poor healing of spinal ligaments, accelerated degeneration of disc and facet joints may occur. The abnormal conditions may persist, and, over time, may lead to chronic back pain via inflammation of neural tissues. The hypothesis explains many of the clinical observations and research findings about the back pain patients. The hypothesis may help in a better understanding of chronic low back and neck pain patients, and in improved clinical management.


Eur Spine J. 2006 May;15(5):668-76. Epub 2005 Jul 27. [PMID:16047209]

Author information: Panjabi MM. Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT 06520-8071, USA.


Free PMC Article

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Abstract

STUDY DESIGN:

Twenty asymptomatic volunteers each received three spinal manipulative treatments to the thoracic spine. The treatments consisted of a straight posterior-to-anterior high-speed, low-amplitude thrust to the transverse process of T3-T10 using a reinforced hypothenar contact. All treatments were given by a full-time practicing clinician with 3 years of experience.

OBJECTIVES:

The primary objective of this study was to quantify local measures of loading applied by the clinician on the volunteers during spinal manipulative treatments and to compare these local measures of loading with previously described global measures.

SUMMARY AND BACKGROUND DATA:

The sparse information on the mechanics of spinal manipulative treatments deals exclusively with global force or pressure measurements. On the basis of these global data, incorrect conclusions may be drawn about the beneficial effects of spinal manipulative therapy, the loading of internal structures, and the risks associated with these treatments.

METHODS:

Twenty asymptomatic subjects each received three posterior-to-anterior, high-speed, low-amplitude spinal manipulative treatments to the transverse process of the thoracic spine. Total force, local force, contact area, peak pressure, and average pressure at the contact interface between clinician and subject were measured continuously by use of a thin, flexible pressure pad. Local and global measures of loading were compared and analyzed by use of nonparametric statistics (alpha = 0.01).

RESULTS:

The average peak total force was 238.2 N. The average peak local force over a target area of 25 mm2 was 5 N, indicating that global measures of loading vastly overestimate the local effective forces at the target site. The peak pressure point moved, on average, 9.8 mm during the course of the manipulation.

CONCLUSIONS:

To the authors’ best knowledge, this is the first study to quantify local, effective measures of loading and compare them with the global measures typically used. The conclusions are limited because the study used a single clinician. The effective loading of specific target sites is much smaller than the global measures might suggest. This result occurs because as the forces during spinal manipulative treatment increase, so does the contact area; therefore, much of the total treatment force is taken up by non-target-specific tissues. Because of the vast discrepancy between the global and local measures of loading, it is suggested that risk-benefit assessments of high-speed, low-amplitude spinal manipulative treatments should be made, including local measures of loading. Finally, because theoretical approaches and the inverse dynamics approach can provide only global measures of loading, the results of such studies should be interpreted with caution.


Spine (Phila Pa 1976). 2001 Oct 1;26(19):2105-10. [PMID:11698887]

Author information: Herzog W, Kats M, Symons B. Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada.

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Abstract

STUDY DESIGN:

The diagnostic performance of a newly described  variable was assessed in an in vivo model of disc degeneration using a  split-pair experimental design.

OBJECTIVE:

To determine if vertebral displacement measures  generated from ultrasonic indentation could distinguish between  experimental and control groups of animals.

SUMMARY OF BACKGROUND DATA:

Few procedures are available that  noninvasively assess subcutaneous vertebral mechanics. Information from  such a procedure would be of value in determining potential clinical  relevance of spinal mechanics with respect to low back pain.

METHODS:

Eight adolescent pigs underwent endplate perforation  surgery to initiate lumbar disc degeneration. After 4 months of  recovery, these and eight age-matched controls were assessed by  ultrasonic indentation, a noninvasive procedure that quantifies  vertebral displacements in the plane of loading-indentation. Each animal  then received a facetectomy and was reindented at the same location as  confirmed by ultrasonic imaging. Discal materials were removed  postmortem for analysis.

RESULTS:

Degenerative discs exhibited morphologic changes  consistent with early degenerative disc disease. Prefacetectomy  comparison of vertebral displacement measures between control and  experimental animals resulted in sensitivity, specificity, and  diagnostic accuracy values of 75.0%, 83.3%, and 77%, respectively. After  facetectomy these values increased to 87.5%, 83.3%, and 85%,  respectively. These measures of diagnostic performance were comparable  or superior to those of existing clinical techniques (invasive or  otherwise) used to assess degenerative conditions of the spine.

CONCLUSIONS:

The results of this study suggest that noninvasive  measures of vertebral displacement are clinically significant and  possess the additional advantages of being objective and noninvasive.


Spine (Phila Pa 1976). 2001 Jun 15;26(12):1348-55. [PMID:11426151]

Author information: Kawchuk GN, Kaigle AM, Holm SH, Rod Fauvel O, Ekström L, Hansson T. Department of Orthopaedics, Sahlgrenska University Hospital, Göteborg, Sweden.

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Abstract

OBJECTIVE:

The objective of this study was to quantify the mobility characteristics (dynamic stiffness and mechanical impedance) of the normal human thoracolumbar spine with a transient vibration analysis technique.

DESIGN:

This study is a prospective clinical investigation to obtain normative biomechanical data from the human male and female spine in vivo.

SETTING:

Musculoskeletal research laboratory, university setting.

SUBJECTS:

Twenty asymptomatic subjects (age range, 20-60 years) with no recent history of musculoskeletal complaints.

MAIN OUTCOME MEASURES:

Mechanical impedance, effective stiffness, and resonant frequency analyses were used to quantify the dynamic stiffness of the thoracolumbar spine in this subject population. Data were obtained from posteroanterior mechanical thrusts delivered with an activator adjusting instrument equipped with a load cell and accelerometer by means of a portable computer.

RESULTS:

In response to the activator adjusting instrument thrusts, the thoracolumbar spine typically exhibited an impedance minimum at frequencies ranging between 30 and 50 Hz. The maximum posteroanterior impedance and corresponding maximum effective stiffness of the thoracolumbar spine and sacrum was roughly 2 to 8 times greater than the magnitude of the impedance minimum. Statistically significant differences in mobility between male and female subjects were noted, particularly for frequencies corresponding to the maximum mobility (40 Hz) and minimum mobility (10-20 Hz, 70-80 Hz). For most subjects (both male and female), the lumbar region exhibited a higher impedance and stiffness (less mobility) when compared with the thoracic region.

CONCLUSIONS:

The posteroanterior mechanical behavior of the human thoracolumbar spine was found to be sensitive to mechanical stimulus frequency and showed significant region-specific and gender differences. In the frequency range of 30 to 50 Hz, the lumbar spine of this subject population is the least stiff and therefore has the greatest mobility. From a biomechanical point-of-view, the results of this study indicate that dynamic spinal manipulative therapy procedures will produce more spinal motion for a given force, particularly when the posteroanterior manipulative thrust is delivered in frequency ranges at or near the resonant frequency. In this regard, spinal manipulative therapy procedures designed to target the resonant frequency of the spine require less force application. Both magnitude and frequency content of manual and mechanical thrusting manipulations may be critical elements for therapeutic outcome.


J Manipulative Physiol Ther. 2000 Oct;23(8):521-30. [PMID:11050608]

Author information: Keller TS, Colloca CJ, Fuhr AW. Department of Mechanical Engineering, University of Vermont, Burlington, VT 05405, USA.

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Introduction:

A biomechanical analysis of the spine is  important for understanding its response to different loading  environments. Although substantial information exists on the dynamic  response of the spine in the axial direction, little is known about the  dynamic response to externally applied, posterior-anterior (PA) directed  forces Such as chiropractic manipulations, in this paper, a  5-degree-of-freedom (DOF), lumped equivalent model the lumbar spine is  developed. Model results are compared to quasi-static, oscillatory and  impulsive force measurements of vertebral motion associated with  mobilization [1], manual manipulation [2] and mechanical force,  manually-assisted (MFMA) adjustments [3].

 

Material and methods:

Five Degree-of Freedom Model A 5-DOF mass, massless-spring and damper model of the lumbar  spine is shown in Fig. 1. This model differs from that of a single-DOF  system in that it has 5 natural frequencies.

Modeling of this multi-DOF structure necessitates one governing  equation of motion for each DOF; in matrix form: [M]d2x/dt2+ [C]dx/dt +  [K]x = [F] (1) where [M] is the mass matrix, [C] is the damping matrix,  [K] is the stiffness matrix, [F] is the PA excitation force matrix, and  x = x(t) is the resulting displacement vector. Here we assume that the  system has zero mass coupling, in which case [M] is diagonal. [K] is  written in terms of the stiffness influence coefficients and is a band  matrix along the diagonal. The equations of motion are solved in modal  space using the eigensolution (i.e. the modal properties) of the  homogeneous equation of motion (free vibration without damping). The  eigenvectors (mode shapes) are then assembled into a mode shape matrix such that[M]= [I] and [K] =[frequencies 2], where {tr} denotes the transpose, [I] is the diagonal identity matrix. Given modal damping ratios for each mode shape i, the 5×5 damping

Using Matlab, the motion response of the spine was studied in  response to a 100 N static load, 100 N sinusoidal oscillation, and 100 N  impulsive force applied to each of the vertebral segments. The  following coefficients were used for the mass matrix (kg) and stiffness  (kN/m) matrix [3]: ml=m2=0.170, m3=m4=m5=0.114; kl=50, k2=40, k3=k4=30, k5=45; l,…5= 0.25 (25% of critical) resulting in damping coefficients CIJ ranging from 40-60 Ns/m.

Results:

The PA damped and undamped natural frequencies predicted by the model  were 44.6 Hz and 46. 1 Hz, respectively. Steady State Response The  steady state response to a PA sinusoidal oscillation, f= Foe is given by  the frequency response function; H(oo)=[K oo2M + iooC] (3)For PA  sinusoidal loading, the model-predicted natural frequency ranged from  39-47 Hz (Fig. 2). At resonance, segmental and inter-segmental P A  displacements were 7.1 mm and 1.7 mm, respectively, for PA thrusts on  L3. PA spine mobilization [1] and manual manipulation [2]  correspond to an oscillatory frequency of ~2 Hz. At 2 Hz segmental and  Inter-segmental displacements were predicted to be 4.0 mm (L3) and 1.5  mm (L3-L4), respectively.

 

Impulsive Force Response: The response to an initial displacement [X0] and velocity [V0] was derived by assuming a solution x = UeM for eq. (1): PA MFMA adjustments produce a damped sinusoidal-like  oscillation With a duration of ~5 ms (impulsive force). Hence, we used  the impulse-momentum principle to estimate V0 (1.84 m/s) for a damped  MFMA oscillation f=466e-1000sin(200(3.14)t). Model predicted L3 and  L3.L4 displacements were 1.25 mm and 0.89 mm, respectively, for PA  impulsive forces at L3.

 

Discussion and Conclusions:

The model predicted PA  oscillatory and impulsive resonant frequency of the lumbar spine Is  consistent with previous experimental findings [3]. Segmental  displacements were over 3-fold greater for manual and mobilization  therapies in comparison to MFMA therapy, but differences in  inter-segmental displacements were less remarkable for these three types  of spinal manipulation.

 


Reference: T.S. Keller and C. J. Colloca; Dynamic  Response of the Human Lumbar Spine: A 5 DOF Lumped Parameter Time and  Frequency Domain Model; Proceeding of the 2000 Meeting of the European Society of  Biomechanics, Dublin, Ireland, August 10-14.

References: [1] M. Lee and N.L. Svensson (1993) JMPT 16:  439-446. [2] I. Gal et al. (1997) JMPT 20: 30.40. [3] T.S. Keller, C.I.  Colloca, and A. W. Fuhr(1999) JMPT 22: 75-86.

Acknowledgements: National Institute of Chiropractic Research; Foundation for the Advancement of Chiropractic Education.

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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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