Application of Advanced Biomechanical Methods in Studying Low Back Pain – Recent Development in Estimation of Lower Back Loads and Large-Array Surface Electromyography and Findings

Low back pain (LBP) is a major public health problem and the leading disabling musculoskeletal disorder globally. A number of biomechanical methods using kinematic, kinetic and/or neuromuscular approaches have been used to study LBP. In this narrative review, we report recent developments in two biomechanical methods: estimation of lower back loads and large-array surface electromyography (LA-SEMG) and the findings associated with LBP. The ability to estimate lower back loads is very important for the prevention and the management of work-related low back injuries based on the mechanical loading model as one category of LBP classification. The methods used for estimation of lower back loads vary from simple rigid link-segment models to sophisticated, optimization-based finite element models. In general, reviewed reports of differences in mechanical loads experienced in lower back tissues between patients with LBP and asymptomatic individuals are not consistent. Such lack of consistency is primarily due to differences in activities under which lower back mechanical loads were investigated as well as heterogeneity of patient populations. The ability to examine trunk neuromuscular behavior is particularly relevant to the motor control model, another category of LBP classification. LA-SEMG not only is noninvasive but also provides spatial resolution within and across muscle groups. Studies using LA-SEMG showed that healthy individuals exhibit highly organized, symmetric back muscle activity patterns, suggesting an orderly recruitment of muscle fibers. In contrast, back muscle activity patterns in LBP patients are asymmetric or multifocal, suggesting lack of orderly muscle recruitment. LA-SEMG was also shown capable of capturing unique back muscle response to manual therapy. In conclusion, estimation of low back load and LA-SEMG techniques demonstrated promising potentials for understanding LBP and treatment effects. Future studies are warranted to fully establish clinical validity of these two biomechanical methods

Biodynamic of the human spine

Back pain -- Back pain risk factors -- Functional Biomechanics of the spine -- Estimation of loads on the spine -- Biodynamic models of spine -- Spine stability -- Analysis of squat and stoop dynamic liftings -- muscle forces and internal spinal loads -- Spinal stability and role of passive stiffness in dynamic squat and stoop lifts -- Computation of trunk equilibrium and stability in free flexion-extension movements at different velocities -- Computation of trunk muscle forces, spinal loads and stability in whole body vibration

Changes in Lumbo-Pelvic Coordination of Individuals with and without Low Back Pain when Wearing a Hip Orthosis

Individuals with low back pain demonstrate an abnormal lumbo-pelvic coordination compared to back-healthy individuals. This abnormal coordination presents itself as a reduction in lumbar contributions and an increase in pelvic rotations during a trunk forward bending and backward return task. This study investigated the ability of a hip orthosis in correcting such an abnormal lumbo-pelvic coordination by restricting pelvic rotation and, hence increasing lumbar contributions. The effects of the hip orthosis on the lumbo-pelvic coordination were investigated in 20 low back pain patients and 20 asymptomatic controls. The orthosis reduced pelvic rotation by 12.7° and increased lumbar contributions by 11%. Contrary to our expectation, orthosis-induced changes in lumbo-pelvic coordination were smaller in patients; most likely because our relatively young patient group had smaller unrestricted pelvic rotations compared to asymptomatic individuals. Considering the observed capability of a hip orthosis in causing the expected changes in lumbo-pelvic coordination when there is a relatively large pelvic contribution to trunk motion, application of a hip orthosis may provide a promising method of correcting abnormal lumbo-pelvic coordination, particularly among patients who demonstrate larger pelvic rotation, that warrants further investigation

Application of advanced biomechanical methods in studying low back pain – recent development in estimation of lower back loads and large-array surface electromyography and findings

Babak Bazrgari,1 Ting Xia2 1F. Joseph Halcomb III, M.D. Department of Biomedical Engineering, University of Kentucky, Lexington, KY, 2Palmer Center for Chiropractic Research, Palmer College of Chiropractic, Davenport, IA, USA Abstract: Low back pain (LBP) is a major public health problem and the leading disabling musculoskeletal disorder globally. A number of biomechanical methods using kinematic, kinetic and/or neuromuscular approaches have been used to study LBP. In this narrative review, we report recent developments in two biomechanical methods: estimation of lower back loads and large-array surface electromyography (LA-SEMG) and the findings associated with LBP. The ability to estimate lower back loads is very important for the prevention and the management of work-related low back injuries based on the mechanical loading model as one category of LBP classification. The methods used for estimation of lower back loads vary from simple rigid link-segment models to sophisticated, optimization-based finite element models. In general, reviewed reports of differences in mechanical loads experienced in lower back tissues between patients with LBP and asymptomatic individuals are not consistent. Such lack of consistency is primarily due to differences in activities under which lower back mechanical loads were investigated as well as heterogeneity of patient populations. The ability to examine trunk neuromuscular behavior is particularly relevant to the motor control model, another category of LBP classification. LA-SEMG not only is noninvasive but also provides spatial resolution within and across muscle groups. Studies using LA-SEMG showed that healthy individuals exhibit highly organized, symmetric back muscle activity patterns, suggesting an orderly recruitment of muscle fibers. In contrast, back muscle activity patterns in LBP patients are asymmetric or multifocal, suggesting lack of orderly muscle recruitment. LA-SEMG was also shown capable of capturing unique back muscle response to manual therapy. In conclusion, estimation of low back load and LA-SEMG techniques demonstrated promising potentials for understanding LBP and treatment effects. Future studies are warranted to fully establish clinical validity of these two biomechanical methods. Keywords: low back pain, low back loads, large-array electromyography, narrative revie

A Model-Based Approach for Estimation of Changes in Lumbar Segmental Kinematics Associated with Alterations in Trunk Muscle Forces

The kinematics information from imaging, if combined with optimization-based biomechanical models, may provide a unique platform for personalized assessment of trunk muscle forces (TMFs). Such a method, however, is feasible only if differences in lumbar spine kinematics due to differences in TMFs can be captured by the current imaging techniques. A finite element model of the spine within an optimization procedure was used to estimate segmental kinematics of lumbar spine associated with five different sets of TMFs. Each set of TMFs was associated with a hypothetical trunk neuromuscular strategy that optimized one aspect of lower back biomechanics. For each set of TMFs, the segmental kinematics of lumbar spine was estimated for a single static trunk flexed posture involving, respectively, 40° and 10° of thoracic and pelvic rotations. Minimum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 0° to 0.7° and 0 mm to 0.04 mm, respectively. Maximum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 2.4° to 7.6° and 0.11 mm to 0.39 mm, respectively. The differences in kinematics of lumbar segments between each combination of two sets of TMFs in 97% of cases for angular deformation and 55% of cases for translational deformation were within the reported accuracy of current imaging techniques. Therefore, it might be possible to use image-based kinematics of lumbar segments along with computational modeling for personalized assessment of TMFs

Alterations in trunk bending stiffness following changes in stability and equilibrium demands of a load holding task

The contribution of the trunk neuromuscular system (TNS) to spine stability has been shown in earlier studies by characterizing changes in antagonistic activity of trunk muscles following alterations in stability demands of a task. Whether and/or how much such changes in the response of TNS to alteration in stability demand of the task alter spinal stiffness remains unclear. To address this research gap, a repeated measure study was conducted on twenty gender-balanced asymptomatic individuals to evaluate changes in trunk bending stiffness throughout the lumbar spine's range of flexion following alterations in both stability and equilibrium demands of a load holding task. Trunk bending stiffness was determined using trunk stiffness tests in upright posture on a rigid metal frame under different equilibrium and stability demands on the lower back. Increasing the stability demand by increasing the height of lifted load ∼30 cm only increased trunk bending stiffness (∼39%) over the lower range of lumbar flexion and under the low equilibrium demand condition. Similarly, increasing the equilibrium demand of the task by increasing the weight of lifted load by 3.5 kg only increased trunk bending stiffness (55%) over the low range of lumbar flexion and under the low stability demand condition. Our results suggest a non-linear relationship between changes in stability and equilibrium demands of a task and the contribution of TNS to trunk bending stiffness. Specifically, alterations in TNS response to changes in stability and equilibrium demand of a given task will increase stiffness of the trunk only if the background stiffness is low

Mechanical Demands on the Lower Back in Patients with Non-Chronic Low Back Pain During a Symmetric Lowering and Lifting Task

There is limited information in the literature related to the lower back loading in patients with LBP, particularly those with non-chronic LBP. Toward addressing such a research gap, a case-control study was conducted to explore the differences in lower back mechanical loads between a group of females (n=19) with non-chronic, non-specific LBP and a group of asymptomatic females (n=19). The differences in lower back mechanical loads were determined when participants completed one symmetric lowering and lifting of a 4.5 kg load at their preferred cadence. The axial, shearing, and moment components of task demand at the time of peak moment component as well as measures of peak trunk kinematics were analyzed. Patient vs. asymptomatic group performed the task with smaller peak thoracic rotation and peak lumbar flexion. While no differences in the moment component of task demand on the lower back between the patients and controls were found, the shearing (40–50 age group) and axial components of task demand were, respectively, larger and smaller in patients vs. controls. Whether alterations in lower back loads in patients with non-chronic LBP are in response to pain or preceded the pain, the long-term exposure to abnormal lower back mechanics may adversely affect spinal structure and increase the likelihood of further injury or pain. Therefore, the underlying reason(s) as well as the potential consequence(s) of such altered lower back mechanics in patients with non-chronic LBP should to be further investigated

Load-relaxation properties of the human trunk in response to prolonged flexion: measuring and modeling the effect of flexion angle

Experimental studies suggest that prolonged trunk flexion reduces passive support of the spine. To understand alterations of the synergy between active and passive tissues following such loadings, several studies have assessed the time-dependent behavior of passive tissues including those within spinal motion segments and muscles. Yet, there remain limitations regarding load-relaxation of the lumbar spine in response to flexion exposures and the influence of different flexion angles. Ten healthy participants were exposed for 16 min to each of five magnitudes of lumbar flexion specified relative to individual flexion-relaxation angles (i.e., 30, 40, 60, 80, and 100%), during which lumbar flexion angle and trunk moment were recorded. Outcome measures were initial trunk moment, moment drop, parameters of four viscoelastic models (i.e., Standard Linear Solid model, the Prony Series, Schapery\u27s Theory, and the Modified Superposition Method), and changes in neutral zone and viscoelastic state following exposure. There were significant effects of flexion angle on initial moment, moment drop, changes in normalized neutral zone, and some parameters of the Standard Linear Solid model. Initial moment, moment drop, and changes in normalized neutral zone increased exponentially with flexion angle. Kelvin-solid models produced better predictions of temporal behaviors. Observed responses to trunk flexion suggest nonlinearity in viscoelastic properties, and which likely reflected viscoelastic behaviors of spinal (lumbar) motion segments. Flexion-induced changes in viscous properties and neutral zone imply an increase in internal loads and perhaps increased risk of low back disorders. Kelvin-solid models, especially the Prony Series model appeared to be more effective at modeling load-relaxation of the trunk

Walking Speed Differentially Alters Spinal Loads in Persons with Traumatic Lower Limb Amputation

Persons with lower limb amputation (LLA) perceive altered motions of the trunk/pelvis during activities of daily living as contributing factors for low back pain. When walking (at a singular speed), larger trunk motions among persons with vs. without LLA are associated with larger spinal loads; however, modulating walking speed is necessary in daily life and thus understanding the influences of walking speed on spinal loads in persons with LLA is of particular interest here. Three-dimensional trunk-pelvic kinematics, collected during level-ground walking at self-selected (SSW) and two controlled speeds (~1.0 and ~1.4 m/s), were obtained for seventy-eight participants: 26 with transfemoral and 26 with transtibial amputation, and 26 uninjured controls (CTR). Using a kinematics-driven, non-linear finite element model of the lower back, the resultant compressive and mediolateral/anteroposterior shear loads at the L5/S1 spinal level were estimated. Peak values were extracted and compiled. Despite walking slower at SSW speeds (~0.21 m/s), spinal loads were 8–14% larger among persons with transfemoral amputation vs. CTR. Across all participants, peak compressive, mediolateral, and anteroposterior shear loads increased with increasing walking speed. At the fastest (vs. slowest) controlled speed, these increases were respectively 24–84% and 29–77% larger among persons with LLA relative to CTR. Over time, repeated exposures to these increased spinal loads, particularly at faster walking speeds, may contribute to the elevated risk for low back pain among persons with LLA. Future work should more completely characterize relative risk in daily life between persons with vs. without LLA by analyzing additional activities and tissue-level responses