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.     

Procedure Selection and Patient Positioning Influence Spine Kinematics During High-Velocity,Low-Amplitude Spinal Manipulation Applied to the Low Back

Objectives

This investigation compared indirect 3-dimensional angular kinematics (position, velocity, and acceleration) of the lumbar spine for 2 different high-velocity, low-amplitude (HVLA) spinal manipulation procedures (lumbar spinous pull or push), and altered initial patient lower limb posture.

Evaluation of Peak Force of a Manually Operated Chiropractic Adjusting Instrument With an Adapter for Use in Animals

Objective

This study was designed to assess the peak force of a manually operated chiropractic adjusting instrument, the Activator Adjusting Instrument 4 (AAI 4), with an adapter for use in animals, which has a 3- to 4-fold smaller contact surface area than the original rubber tip.

Methods

Peak force was determined by thrusting the AAI 4 with the adapter or the original rubber tip onto a load cell. First, the AAI 4 was applied perpendicularly by a doctor of chiropractic onto the load cell. Then, the AAI 4 was fixed in a rigid framework and applied to the load cell. This procedure was done to prevent any load on the load cell before the thrust impulse. In 2 situations, trials were performed with the AAI 4 at all force settings (settings I, II, III, and IV, minimum to maximum, respectively). A total of 50 000 samples per second over a period of 3 seconds were collected.

Results

In 2 experimental protocols, the use of the adapter in the AAI 4 increased the peak force only with setting I. The new value was around 80% of the maximum value found for the AAI 4. Nevertheless, the peak force values of the AAI 4 with the adapter and with the original rubber tip in setting IV were similar.

Conclusion

The adapter effectively determines the maximum peak force value at force setting I of AAI 4.     

Manipulation Peak Forces Across Spinal Regions for Children Using Mannequin Simulators

Objective

The purpose of this work was to create an exploratory database of manipulation treatment force variability as a function of the intent of an experienced clinician sub-specializing in the care of children to match treatment to childhood category. Data of this type are necessary for realistic planning of dose–response and safety studies on therapeutic benefit.

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.     

Vertebral Displacements and Muscle Activity During Manual Therapy: Distinct Behaviors Between Spinal Manipulation and Mobilization

Objective

The purpose of this study was to compare vertebral displacements (absolute and relative) and muscle responses induced by spinal manipulative therapy of short (spinal manipulation) and long (spinal mobilization) impulse duration.

Spinal manipulative therapy for elderly patients with chronic obstructive pulmonary disease: a case series

Objective

The objective of this case series is to report the results of spinal manipulative therapy (SMT) for people with chronic obstructive pulmonary disease (COPD) who were older than 65 years.

Methods

The study design was a prospective case series. Six patients of a long-term care center who were older than 65 years and having COPD underwent a course of 12 SMT sessions over a 4-week period. Each SMT session consisted of manually applied spinal manipulation and instrument-assisted spinal manipulation delivered by a doctor of chiropractic. Lung function measurements were recorded at baseline and at 2 and 4 weeks. The occurrence and type of any adverse events (AEs) related to SMT were recorded at each SMT session.

Results

One male and 5 female patients took part in the study. The average age was 79.1 years (range, 68-89 years). There was a clinically significant increase in forced expiratory volume in the first second after SMT in 4 of the 6 patients at 2 weeks. This was sustained in only 1 patient at 4 weeks. No clinically significant changes were observed for forced vital capacity at 2 or 4 weeks. One hundred forty-four manually applied spinal manipulations and 72 instrument-assisted spinal manipulations were administered during the intervention period. No major or moderate AEs were reported. Only minor AEs were reported after 29% of the intervention sessions, with 1 AE being reported for each patient. All AEs resolved within 48 hours.

Conclusions

This case series offers preliminary evidence that SMT may have the potential to benefit lung function in patients with COPD who are older than 65 years.     

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.     

Evaluating the relationship among cavitation, zygapophyseal joint gapping, and spinal manipulation: an exploratory case series

Objective

This project determined the feasibility of conducting larger studies assessing the relationship between cavitation and zygapophyseal (Z) joint gapping following spinal manipulative therapy (SMT).

Methods

Five healthy volunteers (average age, 25.4 years) were screened and examined against inclusion and exclusion criteria. High-signal magnetic resonance imaging (MRI) markers were fixed to T12, L3, and S1 spinous processes. Scout images were taken to verify the location of the markers. Axial images of the L4/L5 and L5/S1 levels were obtained in the neutral supine position. Following the first MRI, accelerometers were placed over the same spinous processes; and recordings were made from them during side-posture positioning and SMT. The accelerometers were removed, and each subject was scanned in side-posture. The greatest central anterior to posterior Z joint spaces (gap) were measured from the first and second MRI scans. Values obtained from the first scan were subtracted from those of the second, with a positive result indicating an increase in gapping following SMT (positive gapping difference). Gapping difference was compared between the up-side (SMT) joints vs the down-side (non-SMT) joints and between up-side cavitation vs up-side noncavitation joints.

Results

Greater gapping was found in Z joints that received SMT (0.5 ± 0.6 mm) vs non-SMT joints (−0.2 ± 0.6 mm), and vertebral segments that cavitated gapped more than those that did not cavitate (0.8 ± 0.7 vs 0.4 ± 0.5 mm).

Conclusions

A future clinical study is quite feasible. Forty subjects (30 in an SMT group and 10 in a control group) would be needed for appropriate power (0.90).     

The Role of Preload Forces in Spinal Manipulation: Experimental Investigation of Kinematic and Electromyographic Responses in Healthy Adults

Objectives

Previous studies have identified preload forces and an important feature of skillful execution of spinal manipulative therapy (SMT) as performed by manual therapists (eg, doctors of chiropractic and osteopathy). It has been suggested that applying a gradual force before the thrust increases the spinal unit stiffness, minimizing displacement during the thrust. Therefore, the main objective of this study was to assess the vertebral unit biomechanical and neuromuscular responses to a graded increase of preload forces.

Methods

Twenty-three participants underwent 4 different SMT force-time profiles delivered by a servo-controlled linear actuator motor and varying in their preload forces, respectively, set to 5, 50, 95, and 140 N in 1 experimental session. Kinematic markers were place on T6, T7, and T8 and electromyographic electrodes were applied over paraspinal muscles on both sides of the spine.

Results

Increasing preload forces led to an increase in neuromuscular responses of thoracic paraspinal muscles and vertebral segmental displacements during the preload phase of SMT. Increasing the preload force also yielded a significant decrease in sagittal vertebral displacement and paraspinal muscle activity during and immediately after the thrust phase of spinal manipulation. Changes observed during the SMT thrust phase could be explained by the proportional increase in preload force or the related changes in rate of force application. Although only healthy participants were tested in this study, preload forces may be an important parameter underlying SMT mechanism of action. Future studies should investigate the clinical implications of varying SMT dosages.

Conclusion

The present results suggest that neuromuscular and biomechanical responses to SMT may be modulated by preload through changes in the rate of force application. Overall, the present results suggest that preload and rate of force application may be important parameters underlying SMT mechanism of action.     

Best Practices for Chiropractic Care for Older Adults: A Systematic Review and Consensus Update

Objective

The purpose of this study was to update evidence-based recommendations on the best practices for chiropractic care of older adults.

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.     

An experimental study of chest compression during chiropractic manipulation of the thoracic spine using an anthropomorphic test device

Purpose

Chiropractic manipulation of the thoracic spine may induce chest deformations in the anterior-posterior direction. Yet, few studies have examined the biomechanical response of the chest associated with these manipulations. Consequently, an experimental analysis was undertaken to quantify chest compressions resulting from chiropractic thoracic spine manipulations and to estimate amount of risk for injury.

Methods

A 2-part study approach was used with a Hybrid III anthropomorphic test dummy. In part 1, the dummy was positioned prone on a chiropractic table and subjected to thoracic spine manipulation by 2 experienced doctors of chiropractic. Chest compressions were quantified in the anterior-posterior direction. Manipulation forces were self-selected, with “typical” and “maximum” efforts examined. In part 2, the dummy was positioned beneath a force-instrumented mechanical piston device. Using the piston, chest compressions were induced with magnitudes identical to those recorded during chiropractic manipulation as well as magnitudes sufficient to induce injury. In all trials, force measurements were recorded.

Results

Thoracic manipulations incorporating the typical and maximum efforts by the chiropractors resulted in maximum chest compressions attaining 1.8% and 4.5% of total chest depth, respectively. According to previously developed correlations between chest compression and injury severity defined using the Abbreviated Injury Scale (AIS), maximum chest compression measured during this study was only 22.7% of the compression required for greater than 10% risk of an AIS 1 injury. Abbreviated Injury Scale 1 level injuries are graded as minor severity and correspond to sternum contusion or fracture of a single rib.

Conclusions

Results from this preliminary study showed that maximum chest compression during thoracic spine manipulation corresponded to minimal risk of AIS 1 level injuries.     

Comparison of Forces Exerted by a Chiropractor on Children and Adults During High-Speed,Low-Amplitude Spinal Manipulations: A Feasibility Study

ObjectiveThe aim of this study was to demonstrate that quantification of the forces exerted by a single chiropractor on children and adults during high-velocity, low-amplitude spinal manipulations and the correlation of forces to age was feasible.MethodsThe force-time profiles of high-velocity, low-amplitude spinal manipulations were measured in 48 children (109 manipulations) ranging from 14 weeks to 17 years of age, and 20 adults (49 manipulations) in a clinical setting. The measurements were taken using a thin, flexible pressure pad. Outcome variables (peak forces, preload forces, thrust forces, thrust durations, rates of force application, and thrust impulses) were quantified and compared across age groups using Kruskal-Wallis testing with Dunn post hoc analysis. Outcome variables were fitted with best-fitting linear regressions with age as the dependent variable. The level of significance for all statistical tests was set a priori at α = 0.05.ResultsMost outcome variables increased with the age of the patient. Specifically, peak forces, thrust forces, and the rate of force application were positively correlated with age, while thrust durations remained constant across all ages and preload forces decreased slightly with patient age for cervical spine manipulations.ConclusionFor this single chiropractor in private practice, the forces he used increased with the age of the patient, and he thus used lower forces in children than adults. This study shows that measuring the forces used by a chiropractor in clinical practice on patients with a range of ages was feasible.     

A Pilot Randomized Controlled Trial of Flexion-Distraction Dosage for Chiropractic Treatment of Lumbar Spinal Stenosis

Objective

The purpose of this pilot clinical trial was to assess the feasibility of recruiting older adults with lumbar spinal stenosis (LSS) into a clinical trial that used different dosages of flexion-distraction manipulation.

Methods

This randomized controlled trial used a 4-group design. Three groups consisted of chiropractic flexion-distraction manipulation applied at different dosages (8, 12, or 18 treatments). The fourth group was given 8 treatments of placebo care. Feasibility measures included recruitment goals, adherence to various treatment schedules, credibility of the placebo treatment, and rates of adverse events. The primary outcome measure was the Swiss Spinal Stenosis Questionnaire, a validated self-report of LSS symptom severity and physical function.

Results

The recruitment and adherence goals of the study were met with a total of 60 subjects randomized (n = 15 per group) and most subjects attending at least 75% of their scheduled visits. No adverse events were reported by any of the subjects in the trial. Our placebo treatment did not appear to be credible; most subjects correctly guessed that they were receiving a placebo treatment. Between-group effect size estimates were small, indicating larger samples are needed for future studies.

Conclusion

This pilot study showed that it is feasible to recruit patients with LSS and that most subjects will adhere to a 6-week treatment schedule. The information gained from this trial will be useful to inform the design of larger trials.     

Physiological Responses to Spinal Manipulation Therapy: Investigation of the Relationship Between Electromyographic Responses and Peak Force

Objective

It is believed that systematic modulation of spinal manipulative therapy (SMT) parameters should yield varying levels of physiological responses and eventually a range of clinical responses. However, investigation of SMT dose–physiological response relationship is recent and has mostly been conducted using animal or cadaveric models. The main objective of the present study is to investigate SMT dose–physiological response relation in humans by determining how different levels of force can modify electromyographic (EMG) responses to spinal manipulation.

Methods

Twenty-six participants were subjected to 2 trials of 4 different SMT force-time profiles using a servo-controlled linear actuator motor. Normalized EMG activity of paraspinal muscles (left and right muscles at level T6 and T8) was recorded during and after SMT, and EMG values were compared across the varying levels of force.

Results

Increasing the level of force yielded an increase in paraspinal muscle EMG activity during the thrust phase of SMT but also in the two 250-millisecond time windows after the spinal manipulation impulse. These muscle activations quickly attenuated (500 milliseconds after spinal manipulation impulse).

Conclusion

The study confirmed the presence of a local paraspinal EMG response after SMT and highlighted the linear relationship between the SMT peak force and paraspinal muscle activation.     

Outcomes for Chronic Neck and Low Back Pain Patients After Manipulation Under Anesthesia: A Prospective Cohort Study

Background

The purpose of this study was to investigate outcomes of chronic patients unresponsive to previous spinal manipulative therapy subsequently treated with manipulation under anesthesia (MUA).

Methods

A prospective outcome cohort study was performed on 30 patients who had not improved with previous treatment and who underwent a single MUA by a doctor of chiropractic. The numeric rating scale for pain (NRS) and Bournemouth Questionnaire (BQ) were collected at 2 weeks and 1 day before MUA. At 2 and 4 weeks after MUA, the Patient's Global Impression of Change, NRS, and BQ were collected. The intraclass correlation coefficient evaluated stability before treatment. Percentage of patients “improved” was calculated at 2 and 4 weeks. Wilcoxon test compared pretreatment NRS and BQ scores with posttreatment scores. Mann-Whitney U test compared individual questions on the BQ between improved and not improved patients. Logistic regression compared BQ questions to “improvement.”

Results

Good stability of NRS and BQ scores before MUA (intraclass correlation coefficient = 0.46-0.95) was found. At 2 weeks, 52% of the patients reported improvement with 45.5% improved at 4 weeks. Significant reductions in NRS scores at 4 weeks (P = .01) and BQ scores at 2 (P = .008) and 4 weeks (P = .001) were reported. Anxiety/stress levels were significantly different at 2 and 4 weeks between improved and not improved patients (P = .007). None of the BQ questions were predictive of improvement.

Conclusion

Approximately half of patients previously unresponsive to conservative treatment reported clinically relevant improvement at 2 and 4 weeks post-MUA.