Measurement and Analysis of Biomechanical Outcomes of Chiropractic Adjustment Performance in Chiropractic Education and Practice.

OBJECTIVE: The purpose of this study was to compare biomechanical measures of chiropractic adjustment performance of the McTimoney toggle-torque-recoil (MTTR) technique among students and chiropractors. METHODS: Fifty-three participants (15 year-3 [Y3] and 16 year-5 chiropractic students and 22 McTimoney chiropractors [DCs]) participated in this study. Each applied 10 MTTR thrusts to a dynamic load cell, 5 each with their left and right hands. Biomechanical variables including preload force, peak force, time to peak force, thrust duration, and total thrust time were computed from each of the force-time histories and compared within groups using a series of 2-way analysis of variance to evaluate the effects of sex and handedness, and between groups to determine the effect of experience using a series of 3-way analysis of variance. The Games-Howell post hoc test was used to further assess pairwise comparisons. RESULTS: Mean time to peak force was more than 3 × shorter for DCs (69.96 ms) compared with Y3 students (230.36 ms) (P = .030). Likewise, mean thrust duration was also found to be nearly 2.5-fold significantly shorter for DCs (117.77 ms) compared with Y3 students (283.84 ms) (P = .030). The DCs took significantly less total thrust time (mean = 1.27 seconds) in administering MTTR thrusts than Y3 students (1.89 seconds) (P = .006). No significant differences were found among any of the 3 clinician groups for peak force or in time to peak force or thrust duration for comparisons of all 10 MTTR thrusts among year-5 students and DCs. Higher peak forces were observed for thrusts delivered with clinicians' dominant hands (P = .001), and the fastest thrusts were found for the dominant hands of DCs (P = .001). Sex had no significant effect on biomechanical variables. The Y3 students had significant greater variability in thrust times for each hand and for analyses of both hands combined (P = .001). CONCLUSION: Training and experience were found to result in shorter MTTR thrust times and other biomechanical variables that have been identified as important factors in the mechanisms of chiropractic adjustments. Identification of such biomechanical markers as performance outcomes may be of assistance in providing feedback for training in chiropractic education and technique application.

Biomechancial quantification of pathologic manipulable spinal lesions: an in vivo ovine model of spondylolysis and intervertebral disc degeneration.

OBJECTIVE: The purposes of this study were to quantify the biomechanical and pathologic consequences of surgically induced spinal lesions and to determine their response to spinal manipulation (SMT) in an in vivo ovine model. METHODS: Of 24 Merino sheep, 6 received L5 spondylolytic defects, 6 received L1 annular lesions, and 12 served as respective controls. Dorsoventral (DV) stiffness was assessed using oscillatory loads (2-12 Hz). Two SMT force-time profiles were administered in each of the groups using a randomized and repeated-measures design. Stiffness and the effect of SMT on the DV motions and multifidus needle electromyographic responses were assessed using a repeated-measures analysis of variance (α = .05). Postmortem histologic analysis and computed tomography validated the presence of lesions. RESULTS: L5 DV stiffness was significantly increased (40.2%) in the spondylolysis (6.28 N/mm) compared with the L5 control group (4.48 N/mm) (P < 03). Spinal manipulations delivered to the spondylolysis group resulted in less DV vertebral displacement (P < .01) compared with controls. Dorsoventral stiffness of the disc degeneration group was 5.66 N/mm, 94.5% greater than in the L1 control group (2.91 N/mm) (P < .01). One hundred-millisecond SMTs resulted in significantly reduced DV displacements in the disc degeneration group compared with the L1 control group (P < .01). Animals in the disc degeneration group showed a consistent 25% to 30% reduction in needle electromyographic responses to all SMTs. CONCLUSIONS: Quantifiable objective evidence of spinal lesions and their response to SMT were confirmed in this study. Neuromechanical alterations provide novel insights into quantifying manipulable spinal lesions and a means to biomechanically assess SMT outcomes.

Effect of a novel interspinous implant on lumbar spinal range of motion.

Interspinous devices have been introduced to provide a minimally invasive surgical alternative for patients with lumbar spinal stenosis or foraminal stenosis. Little is known however, of the effect of interspinous devices on intersegmental range of motion (ROM). The aim of this in vivo study was to investigate the effect of a novel minimally invasive interspinous implant, InSwing, on sagittal plane ROM of the lumbar spine using an ovine model. Ten adolescent Merino lambs underwent a destabilization procedure at the L1-L2 level simulating a stenotic degenerative spondylolisthesis (as described in our earlier work; Spine 15:571-576, 1990). All animals were placed in a side-lying posture and lateral radiographs were taken in full flexion and extension of the trunk in a standardized manner. Radiographs were repeated following the insertion of an 8-mm InSwing interspinous device at L1-L2, and again with the implant secured by means of a tension band tightened to 1 N/m around the L1 and L2 spinous processes. ROM was assessed in each of the three conditions and compared using Cobb's method. A paired t-test compared ROM for each of the experimental conditions (P < 0.05). After instrumentation with the InSwing interspinous implant, the mean total sagittal ROM (from full extension to full flexion) was reduced by 16% from 6.3 degrees to 5.3 +/- 2.7 degrees. The addition of the tension band resulted in a 43% reduction in total sagittal ROM to 3.6 +/- 1.9 degrees which approached significance. When looking at flexion only, the addition of the interspinous implant without the tension band did not significantly reduce lumbar flexion, however, a statistically significant 15% reduction in lumbar flexion was observed with the addition of the tension band (P = 0.01). To our knowledge, this is the first in vivo study radiographically showing the advantage of using an interspinous device to stabilize the spine in flexion. These results are important findings particularly for patients with clinical symptoms related to instable degenerative spondylolisthesis.

Force-time profile characterization of the McTimoney toggle-torque-recoil technique.

OBJECTIVES: The purpose of this study was to characterize the force-time profile of the McTimoney toggle-torque-recoil (MTTR) technique. METHODS: Two licensed chiropractors trained in the McTimoney Method applied MTTR thrusts to a tabletop where a dynamic load cell had been mounted. Each clinician applied 10 thrusts (5 with each hand) to the load cell in a repeated measures design. Peak forces, time durations, and time to peak force were computed from each of the force-time histories. Descriptive statistics were performed to compare the forces, durations, and times to peak force of the MTTR thrusts. A Mann-Whitney U test compared variables between the 2 clinicians, whereas a Wilcoxon signed-rank test compared right- and left-handed thrusts within clinicians. RESULTS: Considering all MTTR thrusts, the average peak force was 87.22 N (SD = 24.18 N), the average overall thrust duration was 36.38 milliseconds (SD = 9.58 milliseconds), and the average time to peak force was 12.31 milliseconds (S.D. = 4.39 milliseconds). No significant differences in mean peak force, duration, or time to peak force were observed between clinicians. When comparing intraclinician right and left hand thrusts, differences in peak force and duration were observed individually (P < .05). CONCLUSION: For the 2 chiropractors tested, MTTR thrusts were relatively lower in peak force and appreciably faster than other commonly used chiropractic techniques. Future work aims to investigate the relationships between the force-time profiles of MTTR thrusts and resultant physiologic and clinical responses.

Does nanoscale porous titanium coating increase lumbar spinal stiffness of an interbody fusion cage? An in vivo biomechanical analysis in an ovine model.

BACKGROUND: Quantitative objective measures to determine fusion achievement further enable the comparison of new technologies, such as interbody cage surface enhancement. Our aims were to compare in vivo biomechanical responses of ovine L4/5 lumbar motion segments with two cages: 1) Polyetheretherketone or 2) Polyetheretherketone with a nanosurfaced titanium porous scaffold from Nanovis, Inc. METHODS: Fourteen Merino sheep randomly received either 1) standard Polyetheretherketone cage or 2) Nanocoated Polyetheretherketone cage at L4/L5 with autologous bone graft. At baseline and one-year follow-up, dynamic spinal stiffness was quantified in vivo using a validated mechanical assessment at 2 Hz, 6 Hz, and 12 Hz. The dorsoventral secant stiffness (ky = force/displacement, N/mm) and L4-L5 accelerations were determined at each frequency. A repeated measures analysis of variance with Bonferonni correction was used to evaluate within and between group differences among the biomechanical variables. FINDINGS: Both implants increased spinal stiffness at 2 Hz (21 and 39%, respectively, p < .005), and at 6 Hz (12 and 27%, p < .0001). Significantly greater spinal stiffness was observed with Nanocoated Polyetheretherketone at one-year for both frequencies (p < .05). No significant differences were observed at 12 Hz within or between groups. L4-L5 dorsoventral accelerations were significantly decreased one year following cage placement only with Nanocoated Polyetheretherketone (p < .05) and greater reductions in acceleration were observed with Nanocoated Polyetheretherketone compared to standard Polyetheretherketone (p < .05). INTERPRETATION: Both cages increased spinal stiffness, yet, nanosurfaced cages resulted in greater spinal stiffness changes and decreases in L4-L5 accelerations. These findings may assist in clinical decision making and post-operative recovery strategies.

Effects of disc degeneration on neurophysiological responses during dorsoventral mechanical excitation of the ovine lumbar spine.

Mechanisms of spinal manipulation and mobilization include the elicitation of neuromuscular responses, but it is not clear how these responses are affected or altered by disc degeneration. We studied the neurophysiological responses of the normal and degenerated ovine spine subjected to mechanical excitation (varying force amplitude and duration) consistent with spinal manipulative therapy (SMT). Needle electromyographic (EMG) multifidus muscle activation adjacent to the L3 and L4 spinous processes and compound action potentials (CAPs) of the L4 nerve roots were measured during the application of dorsoventral mechanical excitation forces designed to mimic SMT force-time profiles used routinely in clinical practice. The magnitude and percentage of positive EMG responses increased with increasing SMT force magnitude, but not SMT pulse duration, whereas CAP responses were greatest for shorter duration pulses. Disc degeneration was associated with a reduction (20-25%) in positive EMG responses, and a concomitant increase (4.5-10.2%) in CAP responses.

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine.

Posteroanterior spinal stiffness assessments are common in the evaluating patients with low back pain. The purpose of this study was to determine the effects of mechanical excitation frequency on dynamic lumbar spine stiffness. A computer-controlled voice coil actuator equipped with a load cell and LVDT was used to deliver an oscillatory dorsoventral (DV) mechanical force to the L3 spinous process of 15 adolescent Merino sheep. DV forces (48 N peak, approximately 10% body weight) were randomly applied at periodic excitation frequencies of 2.0, 6.0, 11.7 and a 0.5-19.7 Hz sweep. Force and displacement were recorded over a 13-22 s time interval. The in vivo DV stiffness of the ovine spine was frequency dependent and varied 3.7-fold over the 0.5-19.7 Hz mechanical excitation frequency range. Minimum and maximum DV stiffness (force/displacement) were 3.86+/-0.38 and 14.1+/-9.95 N/mm at 4.0 and 19.7 Hz, respectively. Stiffness values based on the swept-sine measurements were not significantly different from corresponding periodic oscillations (2.0 and 6.0 Hz). The mean coefficient of variation in the swept-sine DV dynamic stiffness assessment method was 15%, which was similar to the periodic oscillation method (10-16%). The results indicate that changes in mechanical excitation frequency and animal body mass modulate DV spinal stiffness.

Spinal manipulation force and duration affect vertebral movement and neuromuscular responses.

BACKGROUND: Previous study in human subjects has documented biomechanical and neurophysiological responses to impulsive spinal manipulative thrusts, but very little is known about the neuromechanical effects of varying thrust force-time profiles. METHODS: Ten adolescent Merino sheep were anesthetized and posteroanterior mechanical thrusts were applied to the L3 spinous process using a computer-controlled, mechanical testing apparatus. Three variable pulse durations (10, 100, 200 ms, force = 80 N) and three variable force amplitudes (20, 40, 60 N, pulse duration = 100 ms) were examined for their effect on lumbar motion response (L3 displacement, L1, L2 acceleration) and normalized multifidus electromyographic response (L3, L4) using a repeated measures analysis of variance. FINDINGS: Increasing L3 posteroanterior force amplitude resulted in a fourfold linear increase in L3 posteroanterior vertebral displacement (p < 0.001) and adjacent segment (L1, L2) posteroanterior acceleration response (p < 0.001). L3 displacement was linearly correlated (p < 0.001) to the acceleration response over the 20-80 N force range (100 ms). At constant force, 10 ms thrusts resulted in nearly fivefold lower L3 displacements and significantly increased segmental (L2) acceleration responses compared to the 100 ms (19%, p = 0.005) and 200 ms (16%, p = 0.023) thrusts. Normalized electromyographic responses increased linearly with increasing force amplitude at higher amplitudes and were appreciably affected by mechanical excitation pulse duration. INTERPRETATION: Changes in the biomechanical and neuromuscular response of the ovine lumbar spine were observed in response to changes in the force-time characteristics of the spinal manipulative thrusts and may be an underlying mechanism in related clinical outcomes.

Three-dimensional vertebral motions produced by mechanical force spinal manipulation.

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.

Increased multiaxial lumbar motion responses during multiple-impulse mechanical force manually assisted spinal manipulation.

BACKGROUND: Spinal manipulation has been found to create demonstrable segmental and intersegmental spinal motions thought to be biomechanically related to its mechanisms. In the case of impulsive-type instrument device comparisons, significant differences in the force-time characteristics and concomitant motion responses of spinal manipulative instruments have been reported, but studies investigating the response to multiple thrusts (multiple impulse trains) have not been conducted. The purpose of this study was to determine multi-axial segmental and intersegmental motion responses of ovine lumbar vertebrae to single impulse and multiple impulse spinal manipulative thrusts (SMTs). METHODS: Fifteen adolescent Merino sheep were examined. Tri-axial accelerometers were attached to intraosseous pins rigidly fixed to the L1 and L2 lumbar spinous processes under fluoroscopic guidance while the animals were anesthetized. A hand-held electromechanical chiropractic adjusting instrument (Impulse) was used to apply single and repeated force impulses (13 total over a 2.5 second time interval) at three different force settings (low, medium, and high) along the posteroanterior axis of the T12 spinous process. Axial (AX), posteroanterior (PA), and medial-lateral (ML) acceleration responses in adjacent segments (L1, L2) were recorded at a rate of 5000 samples per second. Peak-peak segmental accelerations (L1, L2) and intersegmental acceleration transfer (L1-L2) for each axis and each force setting were computed from the acceleration-time recordings. The initial acceleration response for a single thrust and the maximum acceleration response observed during the 12 multiple impulse trains were compared using a paired observations t-test (POTT, alpha = .05). RESULTS: Segmental and intersegmental acceleration responses mirrored the peak force magnitude produced by the Impulse Adjusting Instrument. Accelerations were greatest for AX and PA measurement axes. Compared to the initial impulse acceleration response, subsequent multiple SMT impulses were found to produce significantly greater (3% to 25%, P < 0.005) AX, PA and ML segmental and intersegmental acceleration responses. Increases in segmental motion responses were greatest for the low force setting (18%-26%), followed by the medium (5%-26%) and high (3%-26%) settings. Adjacent segment (L1) motion responses were maximized following the application of several multiple SMT impulses. CONCLUSION: Knowledge of the vertebral motion responses produced by impulse-type, instrument-based adjusting instruments provide biomechanical benchmarks that support the clinical rationale for patient treatment. Our results indicate that impulse-type adjusting instruments that deliver multiple impulse SMTs significantly increase multi-axial spinal motion.

Restoring lumbar spine stiffness using an interspinous implant in an ovine model of instability.

BACKGROUND: The objective of this study was to determine the effect of an interspinous implant on lumbar spine stability and stiffness during dorsoventral loading. METHODS: Twelve Merino lambs were mechanically tested in vivo. Oscillatory (2 Hz) loads were applied to L2 under load control while displacements were monitored. Tri-axial accelerometers further quantified adjacent L3-L4 accelerations. Dorsoventral lumbar spine stiffness and L3 and L4 dorsoventral and axial displacements were determined over six trials of 20 cycles of loading. Four conditions were examined: 1) initial intact, 2) following destabilization at L3-L4, 3) following the insertion of an InSwing(®) interspinous device at L3-L4, and 4) with the implant secured with a tension band. Comparisons were performed using a one-way ANOVA with repeated measures and post-hoc Bonferroni correction. FINDINGS: Compared to the intact condition, destabilization significantly decreased lumbar stiffness by 4.5% (P=.001) which was only recovered by the interspinous device with tension band. The interspinous device caused a significant 9.75% (P=.001) increase in dorsoventral stiffness from destabilization that increased 14% with the tension band added (P=.001). The tension band was responsible for decreased displacements from the intact (P=.038), instability (P=.001), and interspinous device (P=.005) conditions. Dorsoventral L3-L4 motion significantly improved with the interspinous device (P=.01) and the addition of the tension band (P=.001). No significant differences in L3-L4 intersegmental stability were noted for axial motion in the sagittal plane. INTERPRETATION: This ovine model provided objective in vivo biomechanical evidence of lumbar instability and its restoration by means of an interspinous implant during dorsoventral spinal loading.

Allogeneic Mesenchymal Precursor Cells Promote Healing in Postero-lateral Annular Lesions and Improve Indices of Lumbar Intervertebral Disc Degeneration in an Ovine Model.

STUDY DESIGN: In-vivo ovine model of intervertebral disc degeneration (IVD) to evaluate treatment with stem cells. OBJECTIVE: To determine if stem cells delivered to the nucleus pulposus (NP) or the annulus fibrosus (AF) of degenerated lumbar IVDs leads to improved indices of disc health. SUMMARY OF BACKGROUND DATA: Previous studies assessing the efficacy of stem cell injections into degenerated IVDs have reported positive findings. However, studies have been limited to small animals, targeting solely the NP, with short term follow-up. METHODS: Mesenchymal precursor cells (MSC) were obtained from the iliac crest of 8-week-old sheep. IVD degeneration was induced by postero-lateral annulotomy at three lumbar levels in eight 2-year-old sheep. Six months later, each degenerated IVD was randomized to one of three treatments: Injection of MSC into (i) previously incised AF (AFI), (ii) NP (NPI), or (iii) no injection (negative control, NC). The adjacent IVD received injection of phosphate buffered saline into NP (positive control, PC). Radiographs and magnetic resonance imaging scans were obtained at baseline, 6, 9, and 12 months. Discs were harvested at 12 months for biochemical and histological analyses. RESULTS: IVD degeneration was consistently observed postannulotomy, and characterized by reduced disc height index (DHI), disc height (DH), glycosaminoglycan (GAG) content, and increased grade of disc degeneration.Six months after stem cell injection, DHI and DH had recovered in AFI and NPI groups when compared with NC group (P < 0.01). Mean Pfirrmann grade improved from 3.25 to 2.67 (AFI group) and from 2.96 to 2.43 (NPI group). Mean histopathological grade improved for both AFI (P < 0.002) and NPI (P < 0.02) groups. Both AFI and NPI groups demonstrated spontaneous repair of the postero-lateral annular lesion. CONCLUSION: In this large animal model, injection of MSCs into the annulus fibrosus or the nucleus pulposus of degenerated IVD resulted in significant improvements in disc health. LEVEL OF EVIDENCE: N/A.

Influence of spine morphology on intervertebral disc loads and stresses in asymptomatic adults: implications for the ideal spine.

BACKGROUND CONTEXT: Sagittal profiles of the spine have been hypothesized to influence spinal coupling and loads on spinal tissues. PURPOSE: To assess the relationship between thoracolumbar spine sagittal morphology and intervertebral disc loads and stresses. STUDY DESIGN: A cross-sectional study evaluating sagittal X-ray geometry and postural loading in asymptomatic men and women. PATIENT SAMPLE: Sixty-seven young and asymptomatic subjects (chiropractic students) formed the study group. OUTCOME MEASURES: Morphological data derived from radiographs (anatomic angles and sagittal balance parameters) and biomechanical parameters (intervertebral disc loads and stresses) derived from a postural loading model. METHODS: An anatomically accurate, sagittal plane, upright posture, quadrilateral element model of the anterior spinal column (C2-S1) was created by digitizing lateral full-spine X-rays of 67 human subjects (51 males, 16 females). Morphological measurements of sagittal curvature and balance were compared with intervertebral disc loads and stresses obtained using a quadrilateral element postural loading model. RESULTS: In this young (mean 26.7, SD 4.8 years), asymptomatic male and female population, the neutral posture spine was characterized by an average thoracic angle (T1-T12) = +43.7 degrees (SD 11.4 degrees ), lumbar angle (T12-S1) = -63.2 degrees (SD 10.0 degrees ), and pelvic angle = +49.4 degrees (SD 9.9 degrees ). Sagittal curvatures exhibited relatively broad frequency distributions, with the pelvic angle showing the least variance and the thoracic angle showing the greatest variance. Sagittal balance parameters, C7-S1 and T1-T12, showed the best average vertical alignment (5.3 mm and -0.04 mm, respectively). Anterior and posterior disc postural loads were balanced at T8-T9 and showed the greatest difference at L5-S1. Disc compressive stresses were greatest in the mid-thoracic region of the spine, whereas shear stresses were highest at L5-S1. Significant linear correlations (p < .001) were found between a number of biomechanical and morphological parameters. Notably, thoracic shear stresses and compressive stresses were correlated to T1-T12 and T4-hip axis (HA) sagittal balance, respectively, but not to sagittal angles. Lumbar shear stresses and body weight (BW) normalized shear loads were correlated with T12-S1 balance, lumbar angle, and sacral angle. BW normalized lumbar compressive loads were correlated with T12-S1 balance and sacral angle. BW normalized lumbar disc shear (compressive) loads increased (decreased) significantly with decreasing lumbar lordosis. Cervical compressive stresses and loads were correlated with all sagittal balance parameters except S1-HA and T12-S1. A neutral spine sagittal model was constructed from the 67 subjects. CONCLUSIONS: The analyses suggest that sagittal spine balance and curvature are important parameters for postural load balance in healthy male and female subjects. Morphological predictors of altered disc load outcomes were sagittal balance parameters in the thoracic spine and anatomic angles in the lumbar spine.

The biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon: a review of literature.

OBJECTIVES: The aim of this study was to review the biomedical literature to ascertain the biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon (FRP). DATA SOURCES: Index Medicus via PubMed, the Noble Science Library's e-journal archives, and the Manual Alternative and Natural Therapy Index System databases were searched using the same search terms. DISCUSSION: The presence of the FRP during trunk flexion represents myoelectric silence consistent with increased load sharing of the posterior discoligamentous passive structures. Passive contributions from erector spinae stretching during the flexion posture and active contributions from other muscles (quadratus lumborum and deep erector spinae among others) further assist in load sharing in the trunk flexion posture. A number of studies have shown differences in the FRP between patients with chronic low back pain and healthy individuals, and the reliability of the assessment. Persistent activation of the lumbar erector spinae musculature among patients with back pain may represent the body's attempt to stabilize injured or diseased spinal structures via reflexogenic ligamentomuscular activation thereby protecting them from further injury and avoiding pain. CONCLUSIONS: The myoelectric silencing of the erector spinae muscles in the trunk flexion posture is indicative of increased load sharing on passive structures, which tissues have been found to fail under excessive loading conditions and shown to be a source of low back pain. The studies that show differences in the presence of the FRP among patients and control subjects are encouraging for this type of clinical assessment and suggest that assessment of the FRP is a valuable objective clinical tool to aid in the diagnosis and treatment of patients with low back pain.

A randomized clinical trial of manual versus mechanical force manipulation in the treatment of sacroiliac joint syndrome.

OBJECTIVE: To investigate the effect of instrument-delivered compared with traditional manual-delivered thrust chiropractic adjustments in the treatment of sacroiliac joint syndrome. METHODS: Prospective, randomized, comparative clinical trial. Sixty patients with sacroiliac syndrome were randomized into two groups of 30 subjects. Each subject received 4 chiropractic adjustments over a 2-week period and was evaluated at 1-week follow-up. One group received side-posture, high-velocity, low-amplitude chiropractic adjustments; the other group received mechanical-force, manually-assisted chiropractic adjustments using an Activator Adjusting Instrument (Activator Methods International, Ltd, Phoenix, Ariz). RESULTS: No significant differences between groups were noted at the initial consultation for any of the outcome variables. Statistically significant improvements were observed in both groups from the first to third, third to fifth, and first to fifth consultations for improvements (P < .001) in mean numerical pain rating scale 101 (group 1, 49.1-23.4; group 2, 48.9-22.5), revised Oswestry Low Back Pain Disability Questionnaire (group 1, 37.4-18.5; group 2, 36.6-15.1), orthopedic rating score (group 1, 7.6-0.6; group 2, 7.5-0.8), and algometry measures (group 1, 4.8-6.5; group 2, 5.0-6.8) for first to last visit for both groups. CONCLUSIONS: The results indicate that a short regimen of either mechanical-force, manually-assisted or high-velocity, low-amplitude chiropractic adjustments were associated with a beneficial effect of a reduction in pain and disability in patients diagnosed with sacroiliac joint syndrome. Neither mechanical-force, manually-assisted nor high-velocity, low-amplitude adjustments were found to be more effective than the other in the treatment of this patient population.

Comparison of mechanical force of manually assisted chiropractic adjusting instruments.

OBJECTIVE: To quantify the force-time and force-delivery characteristics of six commonly used handheld chiropractic adjusting devices. METHODS: Four spring-loaded instruments, the Activator Adjusting Instrument; Activator II Adjusting Instrument, Activator III Adjusting Instrument, and Activator IV Adjusting Instrument, and two electromechanical devices, the Harrison Handheld Adjusting Instrument and Neuromechanical Impulse Adjusting Instrument, were applied to a dynamic load cell. A total of 10 force-time histories were obtained at each of three force excursion settings (minimum to maximum) for each of the six adjusting instruments at preload of approximately 20 N. RESULTS: The minimum-to-maximum force excursion settings for the spring-loaded mechanical adjusting instruments produced similar minimum-to-maximum peak forces that were not appreciably different for most excursion settings. The electromechanical adjusting instruments produced short duration ( approximately 2-4 ms), with more linear minimum-to-maximum peak forces. The force-time profile of the electromechanical devices resulted in a more uniform and greater energy dynamic frequency response in comparison to the spring-loaded mechanical adjusting instruments. CONCLUSIONS: The handheld, electromechanical instruments produced substantially larger peak forces and ranges of forces in comparison to the handheld, spring-loaded mechanical devices. The electromechanical instruments produced greater dynamic frequency area ratios than their mechanical counterparts. Knowledge of the force-time history and force-frequency response characteristics of spinal manipulative instruments may provide basic benchmarks and may assist in understanding mechanical responses in the clinical setting.

Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization.

OBJECTIVE: To develop a mathematical model capable of describing the static and dynamic motion response of the lumbar spine to posteroanterior forces. DESIGN: Static, impulsive and oscillatory forces with varying thrust angles and offsets were applied to the model, and the resulting motion responses were compared to experimental data published for spinal mobilization and manipulation of prone-lying subjects. BACKGROUND: Methods are sought to improve understanding of the dynamic force-induced displacement response of the lumbar spine during spinal mobilization and manipulation treatment. METHODS: The thorax, pelvis and five lumbar vertebrae were represented as seven rigid structures and eight flexible joint structures. Flexible joint structures were modeled using spring and damper elements with three displacement degrees-of-freedom (posterior-anterior and axial displacement, and flexion-extension rotation). The resulting 21 degrees-of-freedom lumped parameter model was solved in modal space. RESULTS: The fundamental natural frequency of vibration was 5.24 Hz. Simulations performed using 100 N static and dynamic posteroanterior forces applied to the L3 vertebrae indicated that peak L3 segmental displacements were up to 2.40 mm (impulsive) and 8.23 mm (oscillatory at 2 Hz). Appreciable axial displacements (0.41 mm) and flexion-extension rotations (1.49 degrees ) were also observed for oscillatory forces at L3. The posteroanterior motion response of the lumbar vertebrae was relatively insensitive to both the thrust force angle and thrust force offset, but axial displacements and flexion-extension rotations showed a large change (2-fold or greater) for thrust angles greater than -5 degrees (caudal) in comparison to vertical thrusts. Intersegmental motion responses for static, impulsive and oscillatory loads were more comparable than their segmental counterparts. CONCLUSIONS: The model predicts lumbar segmental and inter-segmental motion responses to manipulative forces that are otherwise difficult to obtain experimentally. RELEVANCE: This study assists clinicians to understand the biomechanics of posteroanterior forces applied to the lumbar spine of prone-lying subjects. Of particular clinical relevance is the finding that greater spinal mobility is possible by targeting specific load-time histories.

Validation of a noninvasive dynamic spinal stiffness assessment methodology in an animal model of intervertebral disc degeneration.

STUDY DESIGN: An experimental in vivo ovine model of intervertebral disc degeneration was used to quantify the dynamic motion response of the lumbar spine. OBJECTIVE: The purpose of this study was to: (1) compare invasively measured lumbar vertebral bone acceleration responses to noninvasive displacement responses, and (2) determine the effects of a single level degenerative intervertebral disc lesion on these responses. SUMMARY OF BACKGROUND DATA: Biomechanical techniques have been established to quantify vertebral motion responses, yet their invasiveness limits their use in a clinical setting. METHODS: Twenty-five Merino sheep were examined; 15 with surgically induced disc degeneration at L1-L2 and 10 controls. Triaxial accelerometers were rigidly fixed to the L1 and L2 spinous processes and dorsoventral (DV) mechanical excitation (20-80 N, 100 milliseconds) was applied to L3 using a spinal dynamometer. Peak force and displacement and peak-peak acceleration responses were computed for each trial and a least squares regression analysis assessed the correlation between L3 displacement and adjacent (L2) segment acceleration responses. An analysis of covariance (ANCOVA) was performed to test the homogeneity of slopes derived from the regression analysis and to assess the mean differences. RESULTS: A significant, positive, linear correlation was found between the DV displacement of L3 and the DV acceleration measured at L2 for both normal (R = 0.482, P < 0.001) and degenerated disc groups (R = 0.831, P < 0.001). The L3 DV displacement was significantly lower (ANCOVA, P < 0.001) for the degenerated group (mean: 10.39 mm) in comparison to the normal group (mean: 9.07 mm). Mean peak-peak L2-L1 DV acceleration transfer was also significantly reduced from 12.40 m/s to 5.50 m/s in the degenerated animal group (ANCOVA, P < 0.001). CONCLUSION: The findings indicate that noninvasive displacement measurements of the prone-lying animal can be used to estimate the segmental and intersegmental motions in both normal and pathologic spines.