Introduction

1. Effects of Spinal Manipulation on Peak Loading and Trunk Displacement During Unanticipated Trunk Perturbations of Participants with and without Chronic Low Back Pain Matt Linsenmayer1,Andrew J. Ross1, Malissa Corbett1, Terrence Schwing1, Stevan Walkowski2, Brian C. Clark2,3, David A. Goss Jr.3, James S. Thomas1,2,3 1School of Rehabilitation and Communication Sciences, Division of Physical Therapy, Ohio University, 2 Ohio Musculoskeletal & Neurological Institute, 3Department of Biomedical Sciences College of Osteopathic Medicine, Ohio University, Athens, OH Introduction • ▪ Manipulative treatment has been speculated to increase range of motion and relieve pain through modulation of excitability of the sensory and motor portions of the central nervous system. • ▪ While clinical evidence supporting the effectiveness of manual therapies has emerged, less scientific evidence has been offered to explain the effects and mechanisms underlying these treatments limiting the development of rational strategies for using manipulative therapies (Hurwitz et al.,2002; MacDonald & Bell, 1990). • ▪ However, this hypothesis has received few systematic investigations particularly in relation to chronic low back pain (LBP). Accordingly, we systematically examined the short term effects of joint manipulation on motor control through both cortical and spinal reflex properties. We used a combination of biomechanical and electrophysiological techniques (e.g., motion analysis, surface electromyography). • ▪ Primary aim: To determine the effects of chronic LBP and a single high velocity, low amplitude (HVLA) thrust manipulation to a selected segment of the lumbar spine on trunk displacement during unanticipated trunk perturbations in a half-kneeling position. • However, we wish to be able to further explain the reason for the potential change in trunk displacement. • Secondary aim: To examine changes in the peak load, peak impulse, and specific electromyographic (EMG) data (i.e., muscle onset latency, motor-evoked potential) during unanticipated trunk perturbations to further explain the reason for the change in trunk displacement. Figure 3: A participant is depicted prior to a single HVLA thrust manipulation to a selected segment of the lumbar spine. Results Figure 2: A skeletal reconstruction of the participant using Motion Monitor software (version 7.78, Chicago, IL). Figure 1: A participant is depicted secured in the reference frame prior to a perturbation. • Trunk Displacement • ▪ As shown in Figure 4, hip flexion displacement was significantly greater in subjects with chronic LBP (mean= 8.5 ±1.7o) compared to healthy controls (mean= 3.2 ±1.2o)(p= <.02) during a series of unexpected trunk flexion perturbations. • ▪ There was no main effect of time (i.e., pre-HVLA manipulation versus post-HVLA manipulation) on hip flexion displacement (p= .397). • There was no main effect of group (i.e., chronic LBP versus control) (p= .569) or time (p= .133) on the lumbar flexion displacement during a series of unexpected trunk flexion perturbations. • Applied Load • ▪ As shown in Figure 5, the mean peak load during the series of perturbations was significantly greater in healthy controls (mean= 127.3 ±2.10 N) compared to subjects with chronic LBP (mean= 120.6 ±2.96 N) (p= .03). • ▪ There was no main effect of time on the peak load (p= .727) • ▪ There was no main effect of group (p= .539) or time (p= .392) on impulse during the unexpected perturbations (Figure 6). • ElectromyographicData • ▪ No difference in lumbar paraspinal muscle onset latency exists between each group (i.e., chronic LBP versus control) (p= .853) or within subjects when comparing pre- HVLA manipulation data to post-HVLA manipulation data (p= .382) during unexpected trunk flexion perturbations (Figure 7). Methods ▪ A total of eighteen adults (9 male, 9 female) participated in the study. Participants were recruited by flyers posted in the local university community. Chronic LBP ▪ Eight adult participants (3 male, 5 female) ▪ Mean age of 28.5 ±1.25 years ▪ Mean height of 166.7 ±.92 cm ▪ Mean mass of 67.1 ±1.36 kg ▪ McGill Pain Questionnaire- Present Pain Intensity ▪ Mild = 4 participants ▪ Discomforting = 4 participants ▪ Tampa Scale for Kinesiophobia ▪ Mean score = 33.5 Healthy Controls ▪ Ten adult participants (6 male, 4 female) ▪ Mean age of 22.9 ±1.61 years ▪ Mean height of 174.6 ±.73 cm ▪ Mean mass of 69.9 ±1.01 kg ▪ No history of LBP • ▪ All participants provided written informed consent and the protocol was approved by the Institutional Review Board of Ohio University. • ▪ The test setup is depicted in Figure 1. Participants were positioned in the center of a reference frame in a half-kneeling position with proximal thigh secured to isolate trunk movement. A harness on each participant’s thorax served as an attachment for four cables each connected to a 58N weight stack through a low friction pulley at each corner of the reference frame. Each cable had a load cell in series in order to determine the load and impulse during each perturbation. • ▪ Joint movements and excursions following the perturbation were tracked using Vicon Nexus software (version 1.7, Centennial, CO, USA). • ▪ Surface EMG data were recorded bilaterally from four muscles or muscle groups including; 1) the erector spinae, 2) rectus abdominis, 3) external abdominal oblique, and 4) internal abdominal oblique. • Unexpected perturbations were performed by simultaneously releasing a select pair of the weight stacks causing a perturbing force into trunk flexion, extension, side bending (i.e., right and left) or rotation (i.e., right and left). The order of the direction of perturbation was randomized and counterbalanced. • ▪ Twelve perturbations (i.e., two in each of six directions) were performed. Following the initial twelve perturbations, a single HVLA thrust manipulation to a selected lumbar segment was performed outside of the reference frame. • ▪ Twelve perturbations (i.e., two in each of six directions) were randomly repeated. Conclusion Figure 4: The difference in group hip flexion displacement is shown.* indicates a significant difference between groups. Error bars represent the standard error of the mean. Figure 6: Depicted are the mean peak impulses by group and by time (i.e., pre-HVLA manipulation and post-HVLA manipulation) during perturbations. Error bars represent the standard error of the mean. Figure 5: Depicted is the mean peak load during perturbations in each group.* indicates a significant difference between groups. Error bars represent the standard error of the mean. ▪ Our results indicate that a single HVLA thrust manipulation to a segment of the lumbar spine had no effect on 1) lumbar or hip flexion displacement, 2) peak load, 3) impulse, or 4) onset latency of the erector spinae during trunk flexion perturbations. It is unknown if increased dosage of manual or manipulative therapy would have led to significant changes post-HVLA manipulation due to mechanical and/or neurophysiological effects. ▪ Participants with chronic LBP were found to have a significantly greater hip flexion displacement during trunk flexion perturbations. ▪ However, there was no difference between groups in onset latency of the erector spinae during trunk flexion perturbations. This finding, along with findings that the presence of chronic LBP does not systematically alter cortical excitability impacting the motor evoked potential of the erector spinae (Figure 8) (Clark et al., 2011), show that initially there may be no difference in activation of the erector spinae musculature between groups. However, further work is required to determine if there is a difference in motor control or quality of muscle activity (specifically of the hip extensors) after initial activation. ▪ Additionally, the peak load in participants with chronic LBP was significantly less than the peak load in healthy controls. ▪ This difference cannot be explained by a difference in impulse between groups as there was no significant difference found. Since participants with chronic LBP had greater hip excursion during flexion perturbations, it seems likely that these individuals experienced the load over a longer duration leading to a lower peak load. ▪ Quantitative data to confirm explanations for our results requires further study. Specifically, EMG data will be further explored including the duration and amplitude of muscle activation. The activity of the gluteus maximi and hamstring musculature must be assessed to analyze motor control of the hip. In addition, the dosage of manual or manipulative therapy must be increased in order to determine if main effects of time were limited solely due to lack of an adequate intervention. Figure 8: Depicted are motor-evoked potentials in the erector spinae during single-pulse transcranial magnetic stimulation to cortical areas representing the paraspinal musculature. Error bars represent the standard error of the mean. Figure 7:Depicted are mean onset latencies in the erector spinae during trunk flexion perturbation trials. Error bars represent the standard error of the mean.