Characteristics of Paraspinal Muscle Spindle Response to Mechanically Assisted Spinal Manipulation: A Preliminary Report.

OBJECTIVES: The purpose of this preliminary study is to determine muscle spindle response characteristics related to the use of 2 solenoid powered clinical mechanically assisted manipulation (MAM) devices. METHODS: L6 muscle spindle afferents with receptive fields in paraspinal muscles were isolated in 6 cats. Neural recordings were made during L7 MAM thrusts using the Activator V (Activator Methods Int. Ltd., Phoenix, AZ) and/or Pulstar (Sense Technology Inc., Pittsburgh, PA) devices at their 3 lowest force settings. Mechanically assisted manipulation response measures included (a) the time required post-thrust until the first action potential, (b) differences in mean frequency (MF) and mean instantaneous frequency (MIF) 2 seconds before and after MAM, and (c) the time required for muscle spindle discharge (MF and MIF) to return to 95% of baseline after MAM. RESULTS: Depending on device setting, between 44% to 80% (Pulstar) and 11% to 63% (Activator V) of spindle afferents required >6 seconds to return to within 95% of baseline MF values; whereas 66% to 89% (Pulstar) and 75% to 100% (Activator V) of spindle responses returned to within 95% of baseline MIF in <6 seconds after MAM. Nonparametric comparisons between the 22 N and 44 N settings of the Pulstar yielded significant differences for the time required to return to baseline MF and MIF. CONCLUSION: Short duration (<10 ms) MAM thrusts decrease muscle spindle discharge with a majority of afferents requiring prolonged periods (>6 seconds) to return to baseline MF activity. Physiological consequences and clinical relevance of described MAM mechanoreceptor responses will require additional investigation.

The effect of application site of spinal manipulative therapy (SMT) on spinal stiffness.

BACKGROUND CONTEXT: Like other factors that can influence treatment efficacy (eg, dosage, frequency, time of day), the site of treatment application is known to affect various physical interventions such as topical anesthetics and cardiopulmonary resuscitation. Like these examples, spinal manipulative therapy (SMT) is a physical intervention that may exhibit maximal benefit when directed to a specific site. Whereas numerous studies of SMT efficacy have produced mixed results, few studies have taken into account the site of SMT application. PURPOSE: To determine if the site of SMT application modulates the effect of SMT in an anesthetized feline model. STUDY DESIGN: Spinal manipulative therapy applied to specific anatomic locations randomized in a Latin square design with a no-SMT control. OUTCOME MEASURES: Physiologic measures (spinal stiffness). METHODS: Simulated SMT was delivered by a validated mechanical apparatus to the intact lumbar spine of eight anesthetized felines at four unique sites: L6 spinous process, left L6 lamina, left L6 mammillary process, and L7 spinous process. To measure spinal stiffness, a separate indentation load was applied mechanically to the L6 spinous process before and after each SMT application. Spinal stiffness was calculated from the resulting force-displacement curve as the average stiffness (k) and terminal instantaneous stiffness (TIS). RESULTS: Relative to the no-SMT control, significant decreases in spinal stiffness followed the SMT when L6 spinous and L6 lamina were used as the contact site. Terminal instantaneous stiffness significantly decreased -0.48 N/mm (upper, lower 95% confidence interval [-0.86, -0.09]) with L6 spinous as the contact site and decreased -0.44 N/mm (-0.82, -0.05), with the L6 lamina as the contact site. k increased 0.44 N/mm (-0.01, 088), using L6 spinous as the contact site. CONCLUSIONS: Decreases in terminal spinal stiffness were observed after SMT delivered at some application sites but not the others. The results suggest that SMT contact site modulates SMT's effect on spinal stiffness in a feline model. Changes in spinal terminal instantaneous spinal stiffness were similar in magnitude and direction to those observed in symptomatic human subjects who report benefits after SMT.

Effect of spinal manipulation thrust duration on trunk mechanical activation thresholds of nociceptive-specific lateral thalamic neurons.

OBJECTIVE: The objective of this preliminary study was to determine if high-velocity, low-amplitude spinal manipulation (HVLA-SM) thrust duration alters mechanical trunk activation thresholds of nociceptive-specific (NS) lateral thalamic neurons. METHODS: Extracellular recordings were obtained from 18 NS neurons located in 2 lateral thalamic nuclei (ventrolateral [n = 12] and posterior [n = 6]) in normal anesthetized Wistar rats. Response thresholds to electronic von Frey anesthesiometer (rigid tip) mechanical trunk stimuli applied in 3 lumbar directions (dorsal-ventral, 45° caudal, and 45° cranial) were determined before and immediately after the delivery of 3 HVLA-SM thrust durations (time control 0, 100, and 400 milliseconds). Mean changes in mechanical trunk activation thresholds were compared using a mixed model analysis of variance. RESULTS: High-velocity, low-amplitude spinal manipulation duration did not significantly alter NS lateral thalamic neurons' mechanical trunk responses to any of the 3 directions tested with the anesthesiometer. CONCLUSIONS: This study is the first to examine the effect of HVLA-SM thrust duration on NS lateral thalamic mechanical response thresholds. High-velocity, low-amplitude spinal manipulation thrust duration did not affect mechanical trunk thresholds.

Effect of spinal manipulation thrust magnitude on trunk mechanical activation thresholds of lateral thalamic neurons.

OBJECTIVES: High-velocity low-amplitude spinal manipulation (HVLA-SM), as performed by doctors who use manual therapy (eg, doctors of chiropractic and osteopathy), results in mechanical hypoalgesia in clinical settings. This hypoalgesic effect has previously been attributed to alterations in peripheral and/or central pain processing. The objective of this study was to determine whether thrust magnitude of a simulated HVLA-SM alters mechanical trunk response thresholds in wide dynamic range (WDR) and/or nociceptive specific (NS) lateral thalamic neurons. METHODS: Extracellular recordings were carried out in the thalamus of 15 anesthetized Wistar rats. Lateral thalamic neurons having receptive fields, which included the lumbar dorsal-lateral trunk, were characterized as either WDR (n=22) or NS (n=25). Response thresholds to electronic von Frey (rigid tip) mechanical trunk stimuli were determined in 3 directions (dorsal-ventral, 45° caudalward, and 45° cranialward) before and immediately after the dorsal-ventral delivery of a 100-millisecond HVLA-SM at 3 thrust magnitudes (control, 55%, 85% body weight). RESULTS: There was a significant difference in mechanical threshold between 85% body weight manipulation and control thrust magnitudes in the dorsal-ventral direction in NS neurons (P=.01). No changes were found in WDR neurons at either HVLA-SM thrust magnitude. CONCLUSIONS: This study is the first to investigate the effect of HVLA-SM thrust magnitude on WDR and NS lateral thalamic mechanical response threshold. Our data suggest that, at the single lateral thalamic neuron level, there may be a minimal spinal manipulative thrust magnitude required to elicit an increase in trunk mechanical response thresholds.

Neural responses to the mechanical parameters of a high-velocity, low-amplitude spinal manipulation: effect of preload parameters.

OBJECTIVE: The purpose of this study was to determine how the preload that precedes a high-velocity, low-amplitude spinal manipulation (HVLA-SM) affects muscle spindle input from lumbar paraspinal muscles both during and after the HVLA-SM. METHODS: Primary afferent activity from muscle spindles in lumbar paraspinal muscles were recorded from the L6 dorsal root in anesthetized cats. High-velocity, low-amplitude spinal manipulation of the L6 vertebra was preceded either by no preload or systematic changes in the preload magnitude, duration, and the presence or absence of a downward incisural point. Immediate effects of preload on muscle spindle responses to the HVLA-SM were determined by comparing mean instantaneous discharge frequencies (MIF) during the HVLA-SM's thrust phase with baseline. Longer lasting effects of preload on spindle responses to the HVLA-SM were determined by comparing MIF during slow ramp and hold movement of the L6 vertebra before and after the HVLA-SM. RESULTS: The smaller compared with the larger preload magnitude and the longer compared with the shorter preload duration significantly increased (P = .02 and P = .04, respectively) muscle spindle responses during the HVLA-SM thrust. The absence of preload had the greatest effect on the change in MIF. Interactions between preload magnitude, duration, and downward incisural point often produced statistically significant but arguably physiologically modest changes in the passive signaling properties of the muscle spindle after the manipulation. CONCLUSION: Because preload parameters in this animal model were shown to affect neural responses to an HVLA-SM, preload characteristics should be taken into consideration when judging this intervention's therapeutic benefit in both clinical efficacy studies and in clinical practice.

Effects of unilateral facet fixation and facetectomy on muscle spindle responsiveness during simulated spinal manipulation in an animal model.

OBJECTIVES: Manual therapy practitioners commonly assess lumbar intervertebral mobility before deciding treatment regimens. Changes in mechanoreceptor activity during the manipulative thrust are theorized to be an underlying mechanism of spinal manipulation (SM) efficacy. The objective of this study was to determine if facet fixation or facetectomy at a single lumbar level alters muscle spindle activity during 5 SM thrust durations in an animal model. METHODS: Spinal stiffness was determined using the slope of a force-displacement curve. Changes in the mean instantaneous frequency of spindle discharge were measured during simulated SM of the L6 vertebra in the same 20 afferents for laminectomy-only and 19 laminectomy and facet screw conditions; only 5 also had data for the laminectomy and facetectomy condition. Neural responses were compared across conditions and 5 thrust durations (≤ 250 milliseconds) using linear-mixed models. RESULTS: Significant decreases in afferent activity between the laminectomy-only and laminectomy and facet screw conditions were seen during 75-millisecond (P < .001), 100-millisecond (P = .04), and 150-millisecond (P = .02) SM thrust durations. Significant increases in spindle activity between the laminectomy-only and laminectomy and facetectomy conditions were seen during the 75-millisecond (P < .001) and 100-millisecond (P < .001) thrust durations. CONCLUSION: Intervertebral mobility at a single segmental level alters paraspinal sensory response during clinically relevant high-velocity, low-amplitude SM thrust durations (≤ 150 milliseconds). The relationship between intervertebral joint mobility and alterations of primary afferent activity during and after various manual therapy interventions may be used to help to identify patient subpopulations who respond to different types of manual therapy and better inform practitioners (eg, chiropractic and osteopathic) delivering the therapeutic intervention.

Effects of thrust amplitude and duration of high-velocity, low-amplitude spinal manipulation on lumbar muscle spindle responses to vertebral position and movement.

OBJECTIVE: Mechanical characteristics of high-velocity, low-amplitude spinal manipulations (HVLA-SMs) can vary. Sustained changes in peripheral neuronal signaling due to altered load transmission to a sensory receptor's local mechanical environment are often considered a mechanism contributing to the therapeutic effects of spinal manipulation. The purpose of this study was to determine whether variation in an HVLA-SM's thrust amplitude and duration alters the neural responsiveness of lumbar muscle spindles to either vertebral movement or position. METHODS: Anesthetized cats (n = 112) received L6 HVLA-SMs delivered to the spinous process. Cats were divided into 6 cohorts depending upon the peak thrust force (25%, 55%, 85% body weight) or thrust displacement (1, 2, 3 mm) they received. Cats in each cohort received 8 thrust durations (0-250 milliseconds). Afferent discharge from 112 spindles was recorded in response to ramp and hold vertebral movement before and after the manipulation. Changes in mean instantaneous frequency (∆MIF) during the baseline period preceding the ramps (∆MIFresting), during ramp movement (∆MIFmovement), and with the vertebra held in the new position (∆MIFposition) were compared. RESULTS: Thrust duration had a small but statistically significant effect on ∆MIFresting at all 6 thrust amplitudes compared with control (0-millisecond thrust duration). The lowest amplitude thrust displacement (1 mm) increased ∆MIFresting at all thrust durations. For all the other thrust displacements and forces, the direction of change in ∆MIFresting was not consistent, and the pattern of change was not systematically related to thrust duration. Regardless of thrust force, displacement, or duration, ∆MIFmovement and ∆MIFposition were not significantly different from control. CONCLUSION: Relatively low-amplitude thrust displacements applied during an HVLA-SM produced sustained increases in the resting discharge of paraspinal muscle spindles regardless of the duration over which the thrust was applied. However, regardless of the HVLA-SM's thrust amplitude or duration, the responsiveness of paraspinal muscle spindles to vertebral movement and to a new vertebral position was not affected.

Relationship between Biomechanical Characteristics of Spinal Manipulation and Neural Responses in an Animal Model: Effect of Linear Control of Thrust Displacement versus Force, Thrust Amplitude, Thrust Duration, and Thrust Rate.

High velocity low amplitude spinal manipulation (HVLA-SM) is used frequently to treat musculoskeletal complaints. Little is known about the intervention's biomechanical characteristics that determine its clinical benefit. Using an animal preparation, we determined how neural activity from lumbar muscle spindles during a lumbar HVLA-SM is affected by the type of thrust control and by the thrust's amplitude, duration, and rate. A mechanical device was used to apply a linear increase in thrust displacement or force and to control thrust duration. Under displacement control, neural responses during the HVLA-SM increased in a fashion graded with thrust amplitude. Under force control neural responses were similar regardless of the thrust amplitude. Decreasing thrust durations at all thrust amplitudes except the smallest thrust displacement had an overall significant effect on increasing muscle spindle activity during the HVLA-SMs. Under force control, spindle responses specifically and significantly increased between thrust durations of 75 and 150 ms suggesting the presence of a threshold value. Thrust velocities greater than 20-30 mm/s and thrust rates greater than 300 N/s tended to maximize the spindle responses. This study provides a basis for considering biomechanical characteristics of an HVLA-SM that should be measured and reported in clinical efficacy studies to help define effective clinical dosages.

Radiographic analysis of the anterior to posterior open mouth (APOM) cervical spine view: frequency of atlas transverse process overlap of the inferior tip of the mastoid process.

OBJECTIVE: The purpose of this study was to measure the frequency with which the atlas transverse process is overlapped by the inferior tip of the mastoid process based upon radiographic analysis of the anterior to posterior open mouth (APOM) cervical spine view. METHODS: This is a retrospective study. Anterior to posterior open mouth radiographs (N = 120) were obtained from patient files at a chiropractic clinic. Dimensions were bilaterally measured: the vertical distance from the inferior mastoid to the superior margin of the C1 transverse process (C1TP) and the vertical distance from the inferior mastoid to the inferior margin of the C1TP. The percentage of the C1TP occluded by the mastoid process was calculated by determining the occlusal distance. These percentages were grouped into 4 categories: no occlusion, 1% to 50%, 50% to 99%, and 100%. RESULTS: The occlusal distance for the left and right ranged from -7.1 to 19.0 mm and -7.5 to 19.5 mm, respectively. The mean occlusal distance was identical on the left and right sides (4.6 [SD, 5.1 mm] and 4.7 mm [SD, 5.0 mm], respectively). The percentage of occlusion for the left and right transverse processes ranged from 0% to 80% and 0% to 100%, respectively. The mean percentage was 6.4% (SD, 16.4) on the left and 6.2% (SD, 16.3) on the right. CONCLUSION: This study shows that the occlusal distance for the left and right ranged from -7.1 to 19.0 mm and -7.5 to 19.5 mm, respectively. A total occlusion of the C1TP occurred in 1 side of 120 participants in this sample.

Relationships between joint motion and facet joint capsule strain during cat and human lumbar spinal motions.

OBJECTIVE: The lumbar facet joint capsule (FJC) is innervated with mechanically sensitive neurons and is thought to contribute to proprioception and pain. Biomechanical investigations of the FJC have commonly used human cadaveric spines, whereas combined biomechanical and neurophysiological studies have typically used nonhuman animal models. The purpose of this study was to develop mathematical relationships describing vertebral kinematics and FJC strain in cat and human lumbar spine specimens during physiological spinal motions to facilitate future efforts at understanding the mechanosensory role of the FJC. METHODS: Cat lumbar spine specimens were tested during extension, flexion, and lateral bending. Joint kinematics and FJC principal strain were measured optically. Facet joint capsule strain-intervertebral angle (IVA) regression relationships were established for the 3 most caudal lumbar joints using cat (current study) and human (prior study) data. The FJC strain-IVA relationships were used to estimate cat and human spine kinematics that corresponded to published sensory neuron response thresholds (5% and 10% strain) for low-threshold mechanoreceptors. RESULTS: Significant linear relationships between IVA and strain were observed for both human and cat during motions that produced tension in the FJCs (P < .01). During motions that produced tension in the FJCs, the models predicted that FJC strain magnitudes corresponding to published sensory neuron response thresholds would be produced by IVA magnitudes within the physiological range of lumbar motion. CONCLUSIONS: Data from the current study support the proprioceptive role of lumbar spine FJC and low-threshold mechanoreceptive afferents and can be used in interpreting combined neurophysiological and biomechanical studies of cat lumbar spines.

Performance and reliability of a variable rate, force/displacement application system.

OBJECTIVE: Spinal manipulation therapy (SMT), an intervention used to treat low back pain, has been demonstrated to affect the stiffness of the spine. To adequately quantify the effects of SMT on stiffness, a device capable of applying specific parameters of manipulation in addition to measuring force-displacement values has been developed previously. Previously developed indentation techniques that quantify stiffness have been modified for novel use in evaluating SMT parameters. The reliability of stiffness measurements performed by the newly adapted device was assessed in this study. METHODS: Seven springs of varying stiffness were each indented 10 times by a variable rate force/displacement (VRFD) device. Indentations were performed at a rate of 0.5 mm/s to a maximal displacement of 4 mm. The stiffness coefficients for a middle portion of the resulting force-displacement graph and the terminal instantaneous stiffness (stiffness at end displacement) were calculated. The intraclass correlation and confidence interval were calculated for these stiffness measurements to assess device reliability. RESULTS: Repeated spring stiffness measures yielded an intraclass correlation coefficient value of 1.0. The mean stiffness values had narrow 95% confidence intervals ranging from 0.01 N/mm to 0.06 N/mm and small coefficients of variation. CONCLUSION: This VRFD device provides highly reliable stiffness measurements in controlled conditions. Although in vivo reliability remains to be established, the results of this study support the use of the VRFD device in future trials investigating the impact of various SMT parameters on spinal stiffness.

Response of lumbar paraspinal muscles spindles is greater to spinal manipulative loading compared with slower loading under length control.

BACKGROUND CONTEXT: Spinal manipulation (SM) is a form of manual therapy used clinically to treat patients with low back and neck pain. The most common form of this maneuver is characterized as a high-velocity (duration <150 ms), low-amplitude (segmental translation <2 mm, rotation <4 degrees , and applied force 220-889 N) impulse thrust (high-velocity, low-amplitude spinal manipulation [HVLA-SM]). Clinical skill in applying an HVLA-SM lies in the practitioner's ability to control the duration and magnitude of the load (ie, the rate of loading), the direction in which the load is applied, and the contact point at which the load is applied. Control over its mechanical delivery is presumably related to its clinical effects. Biomechanical changes evoked by an HVLA-SM are thought to have physiological consequences caused, at least in part, by changes in sensory signaling from paraspinal tissues. PURPOSE: If activation of afferent pathways does contribute to the effects of an HVLA-SM, it seems reasonable to anticipate that neural discharge might increase or decrease in a nonlinear fashion as the thrust duration approaches a threshold value. We hypothesized that the relationship between the duration of an impulsive thrust to a vertebra and paraspinal muscle spindle discharge would be nonlinear with an inflection near the duration of an HVLA-SM delivered clinically (<150 ms). In addition, we anticipated that muscle spindle discharge would be more sensitive to larger amplitude thrusts. STUDY DESIGN/SETTING: A neurophysiological study of spinal manipulation using the lumbar spine of a feline model. METHODS: Impulse thrusts (duration: 12.5, 25, 50, 100, 200, and 400 ms; amplitude 1 or 2 mm posterior to anterior) were applied to the spinous process of the L6 vertebra of deeply anesthetized cats while recording single unit activity from dorsal root filaments of muscle spindle afferents innervating the lumbar paraspinal muscles. A feedback motor was used in displacement control mode to deliver the impulse thrusts. The motor's drive arm was securely attached to the L6 spinous process via a forceps. RESULTS: As thrust duration became shorter, the discharge of the lumbar paraspinal muscle spindles increased in a curvilinear fashion. A concave-up inflection occurred near the 100-ms duration eliciting both a higher frequency discharge compared with the longer durations and a substantially faster rate of change as thrust duration was shortened. This pattern was evident in paraspinal afferents with receptive fields both close and far from the midline. Paradoxically, spindle afferents were almost twice as sensitive to the 1-mm compared with the 2-mm amplitude thrust (6.2 vs. 3.3 spikes/s/mm/s). This latter finding may be related to the small versus large signal range properties of muscle spindles. CONCLUSIONS: The results indicate that the duration and amplitude of a spinal manipulation elicit a pattern of discharge from paraspinal muscle spindles different from slower mechanical inputs. Clinically, these parameters may be important determinants of an HVLA-SM's therapeutic benefit.

Development of an evidence-based application and rubric for evaluating applicants' qualifications for promotion to professor.

OBJECTIVE: Every promotion committee is challenged by the need to make value judgments on the quantity and quality of peer work. Decisions based upon subjective assessments may not do justice to the applicant's or the institution's needs. The purpose of this article is to (1) describe the process a college promotion committee used to increase the objectivity brought to this activity, (2) present the tools developed that facilitated the collection and evaluation of faculty work, and (3) describe their usage in a promotion cycle. METHODS: The Professor Promotion Committee met weekly for 6 months engaging in lengthy and comprehensive discourse to capture the breadth of scholastic and service activities normally engaged in by faculty. RESULTS: The committee's work culminated in the development of 4 electronic applications soliciting specific evidence aligned with faculty work and 1 scoring rubric tied directly to the e-applications. More than 55 activities were identified, divided into 4 levels of accomplishment using quantitative and qualitative criteria and weighted according to their centrality to faculty work and relative importance to the institution. Each activity was assigned to one of the following categories: teaching/academic support, scholarship/research, service, and professional development. A consensus score based upon the evidence was used to generate promotion discussions. CONCLUSIONS: The committee believes the online application aids applicants in recognizing the breadth and depth of promotable work. It provides them the opportunity to structure their work in ways that enhance their chances for promotion. The evidence-based rubric helps to reduce subjectivity in the evaluation process.

Paraspinal muscle spindle responses to the duration of a spinal manipulation under force control.

OBJECTIVE: More than 90% of chiropractic patients receive high-velocity, low-amplitude spinal manipulation (HVLA-SM) as part of their chiropractic care. The purpose of the current study was determine how the duration of a lumbar HVLA-SM given under force control affects the discharge of paraspinal muscle spindle afferents. METHODS: Experiments were performed on deeply anesthetized adult cats treated in accordance with the Guiding Principles in the Care and Use of Animals approved by the American Physiological Society. Muscle spindle afferents were identified in the dorsal roots. Neural activity was recorded from individual spindles located in the low back predominately from multifidus and longissimus muscles. Spinal manipulative loads were applied to the L6 vertebra. Force-time profiles were half-sine waves with impulse durations of 25, 50, 100, 200, 400, and 800 milliseconds, delivered at constant magnitudes of 33%, 66%, or 100% body weight. The relationships between spinal manipulation duration and muscle spindle responses were determined using a randomized block design. RESULTS: Mean instantaneous discharge frequency increased with decreasing impulse duration. There appeared to be a threshold effect for impulse duration below which the increase in muscle spindle discharge changed greatly with decreasing impulse duration and above which the discharge did not substantially change with decreasing impulse duration. This threshold was in the vicinity of the duration of an HVLA-SM applied clinically (

Spinal manipulation alters electromyographic activity of paraspinal muscles: a descriptive study.

OBJECTIVE: To examine the effect of spinal manipulation on electromyographic (EMG) activity in areas of localized tight muscle bundles of the low back. METHODS: Surface EMG activity was collected from 16 participants in 2 chiropractic offices during the 5 to 10 minutes of the treatment protocol. Electrodes were placed over the 2 sites of greatest paraspinal muscle tension as determined by manual palpation. Spinal manipulation was administered to 8 participants using Activator protocol; the other 8 were treated using Diversified protocol. RESULTS: Electromyographic activity decreased by at least 25% after treatment in 24 of the 31 sites that were monitored. There was less than 25% change at 3 sites and more than 25% increase at 4 sites. Multiple distinct increases and decreases were observed in many data plots. CONCLUSION: The results of this study indicate that manipulation induces a virtually immediate change, usually a reduction, in resting EMG levels in at least some patients with low back pain and tight paraspinal muscle bundles. In some cases, EMG activity increased during the treatment protocol and then usually, but not always, decreased to a level lower than the pretreatment level.