Lumbar spinal disorders including radial\u00a0 tears, disc degeneration, segmental instability and segmental\u00a0 dysfunction have been considered common causes of persistent back pain\u00a0 and sciatica. Such disorders may be characterized as exhibiting\u00a0 alterations in the mechanical behavior to loading, notably, changes in\u00a0 spinal stiffness. Studies investigating posteroanterior (PA) forces in\u00a0 spinal stiffness assessment have shown relationships to spinal level,\u00a0 body type, and lumbar extensor muscle activity. Such measures may be\u00a0 important determinants to discriminate between patients with low back\u00a0 pain and asymptomatic subjects. However, little objective evidence is\u00a0 available discerning variations in PA stiffness, a more complete\u00a0 assessment based upon dynamic stiffness measurements (driving-point\u00a0 impedance) and concomitant neuromuscular response may offer more\u00a0 information concerning mechanical properties of the low back, Thus, the\u00a0 aim of the current study was to determine the stiffness and\u00a0 neuromuscular characteristics of the asymptomatic and symptomatic low\u00a0 back,<\/p>\n
This study is a prospective clinical study\u00a0 investigating the mechanical and muscular behavior of lumbar spinal\u00a0 segments to high loading rate PA forces, 22 subjects (12 male & 10\u00a0 female, mean age of 42.8+ or \u2013 17.5 years, range 15-73 years) underwent a\u00a0 comprehensive physical examination consisting of history,\u00a0 orthopedic\/neurologic examination, lumbar range of motion, pressure\u00a0 algometry and plain film radiographic exanimation of the lumbar spine. A\u00a0 visual analog score (VAS), Oswestry Low Back Disability Index, and\u00a0 Health Status Questionnaire (SF-36) were obtained for all subjects and\u00a0 categorization was made on the basis of symptom frequency, as well as\u00a0 positive vs. negative orthopedic exam, acute vs. chronic (>12 weeks)\u00a0 low back pain (LBP) history and electromyography (EMG) response to PA\u00a0 mechanical stimulation. Each subject was placed in the prone position by\u00a0 use of a motorized vertical\/horizontal table. Surface, linear\u00a0 enveloped, EMG recordings were obtained from electrodes (8 lead s)\u00a0 located over the L3 and L5 paraspinal musculature to monitor the\u00a0 bilateral neuromuscular activity of the erector spinae group during the\u00a0 PA stiffness measurement protocol, Prior to and immediately following\u00a0 the PA mechanical stimulation, each subject performed three consecutive\u00a0 maximal effort isometric trunk extensions to normalize EMG data. A\u00a0 hand-held Activator II Adjusting Instrument equipped with a load cell\u00a0 and accelerometer was used to deliver high rate (<0.1 msec ) PA\u00a0 mechanical stimulation (450 N) to several common spinal landmarks\u00a0 including the PSIS, sacral base and L5, L4, L2, T12, T8 spinous and\u00a0 transverse processes. Driving point impedance (Z, Ns\/m) was calculated\u00a0 for each of the thrusts, from which the effective dynamic stiffness (Z x\u00a0 2(3.21)f) was determined.<\/p>\n
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 (\u2265\u00a010% 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.<\/p>\n
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.<\/p>\n
Reference: <\/strong>Christopher J. Colloca, D.C., Tony S. Keller,\u00a0 Ph.D. , Arlan W. Fuhr, D.C.; Muscular And Mechanical Behavior Of The\u00a0 Lumbar Spine In Response To Dynamic Posteroanterior Forces; Proceedings\u00a0 of the 26th Annual Meeting of the International Society for the Study of\u00a0 the Lumbar Spine, Kona, Hawaii. Toronto: ISSLS, 1999: 136A.<\/p>\n