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Activator Methods International Ltd.
2950 N. Seventh Street, Suite 200
Phoenix, AZ 85014
ofc 602-224-0220
fax 602-224-0230
toll free 1-800-598-0224
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Subject:The Activator® Adjusting Instrument – Biomechanical
Title:Muscular And Mechanical Behavior Of The Lumbar Spine In Response To Dynamic Posteroanterior Forces
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.
Abstract:
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.
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