Christian Larivière

Disability Prevention: New Paradigm for the Management of Occupational Back Pain

Occupational back pain is a widespread self-limited but recurring disease that generates major societal costs and impairs workplace productivity. However, this societal impact is mostly accounted for by a small fraction of patients with back pain who have prolonged absence from work, i.e. prolonged disability.Evidence from research from the past 2 decades has progressively shown that most efforts to prevent or cure the disease have limited results, explaining the expanding number of disability cases from back pain. However, recent evidence has also shed light on the causes of disability that are not only due to the patients’s personal characteristics (physical and psychosocial), but also stem from the patients’s environment in the disability problem — the workplace, the compensation system and even the healthcare delivery system.In addition, successful intervention studies have used an approach to disability prevention through patient reassurance and interventions linked to the workplace, instead of using a medical model of back pain treatment. It is evident that the present disease treatment paradigm should be replaced by a disability prevention paradigm for patients with subacute or chronic back pain to avoid unnecessary evolution towards prolonged disability.We propose a disability prevention management model to encourage clinicians, employers, unions and insurers, as well as researchers in the field, to work within the perspective of the disability paradigm.

Surface electromyography assessment of back muscle intrinsic properties

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.

Comparison of trunk muscle forces and spinal loads estimated by two biomechanical models

BACKGROUND Comparative studies between single-joint electromyography (EMG)- and optimization-driven models of the human spine in estimating trunk muscle and spinal compression forces have not been conclusive. Due to associated implications in ergonomic applications as well as prevention and treatment managements of low-back disorders, there is a need to critically compare existing single- and multi-joint spine models. METHODS A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5-S1 or L4-L5) EMG-driven model (EMGAO) and a multi-joint (T1-S1) Kinematics-driven finite element model (KD) of the spine under different static lifting activities in upright standing posture is carried out. Identical geometry for the spine and trunk musculature as well as passive properties are used in both models. Required model inputs including kinematics, force plate and surface EMG data are collected from one asymptomatic male subject. FINDINGS Contrary to somewhat similar external moments (with differences <11 Nm) as well as comparable compression forces at the L4-S1 joints (<20% except in the heaviest task with 52% difference) and sum of all trunk muscle forces (<26% except in the heaviest task with 44% difference), both models recruited trunk global and local lumbar muscles in markedly different proportions (ratio of total global over total local muscle forces in cases with load in hands remained >2.4 in the KD model whereas <1.0 in the EMGAO model) which in turn led to significantly different shear force estimates. Results of the EMGAO model were level dependent. Estimated L4-L5 intradiscal pressures were comparable to the measured data except for the heaviest task in which case the EMGAO model overestimated the measured pressure by 67%. INTERPRETATION Differences in predictions between these modeling approaches vary depending on the task simulated and the joint considered in the single-joint models of the spine. Such studies are essential to critically evaluate relative performance of existing models and to propose modifications to improve accuracy in estimations. Ergonomic and clinical applications of such model studies should, hence, be carried out with due attention to associated underlying assumptions and shortcomings.

Comparative ability of EMG, optimization, and hybrid modelling approaches to predict trunk muscle forces and lumbar spine loading during dynamic sagittal plane lifting.

OBJECTIVE To compare the ability of three modelling approaches to resolve the muscle and joint forces in a lumbar spine model during dynamic sagittal plane lifting. DESIGN Trunk muscle forces, spine compression, and coactivity predicted through double linear optimization, EMG-assisted, and EMG assisted by optimization approaches were compared.Background. The advantages of EMG-based approaches are known from static task analyses. Limited assessment has been made for dynamic lifting. METHODS Eleven male subjects performed sagittal plane lifting-lowering at fixed cadence from 0 degrees to 45 degrees of trunk flexion with and without an external load of 12 kg. Three-dimensional kinematics and dynamics as well as surface EMG provided inputs to a 12 muscle lumbar spine model. RESULTS Trunk muscle coactivity was different between the modelling approaches but spine compression was not. Both EMG-based approaches were sensitive to trunk muscle coactivity and imbalance in left-right muscle forces during sagittal plane lifting. Overall, the best correlations between predicted forces and EMG as well as between forces predicted by different modelling approaches were obtained with the EMG-based models. Only the EMG assisted by optimization approach simultaneously satisfied mechanical and physiological validity. CONCLUSIONS Both EMG-based approaches demonstrated their potential to detect individual trunk muscle strategies. A more detailed trunk anatomy representation would improve the EMG-assisted approach and reduce the adjustment to muscle force gain through EMG assisted by optimization. RELEVANCE Injury to the lumbar spine could command alternative strategies of motion to attenuate pain and damage. To understand these strategies, the ideal lumbar spine model should predict individual muscle force patterns and satisfy mechanical equilibrium.

A comparative study of two trunk biomechanical models under symmetric and asymmetric loadings

Despite recent advances in modeling of the human spine, simplifying assumptions are still required to tackle complexities. Such assumptions need to be scrutinized to assess their likely impacts on predictions. A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5-S1) optimisation-assisted EMG-driven (EMGAO) and a multi-joint Kinematics-driven (KD) model of the spine under symmetric (symmetric trunk flexion from neutral upright to maximum forward flexion) and asymmetric (holding a load at various heights in the right hand) activities is carried out. Regardless of the task simulated, the KD model predicted greater activities in extensor muscles as compared to the EMGAO model. Such differences in the symmetric tasks was due mainly to the distinct approaches to resolve the redundancy while in the asymmetric tasks they were due also to the different methods used to estimate joint moments. Shear and compression forces were generally higher in the KD model. Differences in predictions between these modeling approaches varied depending on the task simulated and the joint considered in the single-joint EMGAO model. The EMGAO model should incorporate a multi-joint strategy to satisfy equilibrium at different levels while the KD model should benefit from recorded EMG activities of the antagonistic muscles to supplement input measured kinematics.

Psychological influences on repetition-induced summation of activity-related pain in patients with chronic low back pain.

Abstract This study examined the role of pain catastrophizing, fear of movement and depression as determinants of repetition‐induced summation of activity‐related pain. The sample consisted of 90 (44 women and 46 men) work‐disabled individuals with chronic low back pain. Participants were asked to lift a series of 18 canisters that varied according to weight (2.9 kg, 3.4 kg, 3.9 kg) and distance from the body. The canisters were arranged in a 3 × 6 matrix and the weights were distributed such that each ‘column’ of three canisters was equated in terms of physical demands. Participants rated their pain after each lift, and in a separate trial, estimated the weight of each canister. Mean activity‐related pain ratings were computed for each Column of the task. An index of repetition‐induced summation of pain was derived as the change in pain ratings across the six ‘columns’ of the task. Pain catastrophizing, fear of movement and depression were significantly correlated with condition‐related pain (e.g., MPQ) and activity‐related pain ratings. Women rated their pain as more intense than men, and estimated weights to be greater than men. A repetition‐induced summation of pain effect was observed where pain ratings increased as participants lifted successive canisters. Fear of movement, but not pain catastrophizing or depression, was associated with greater repetition‐induced summation of pain. The findings point to possible neurophysiological mechanisms that could help explain why fear of pain is a robust predictor of pain‐related disability. Mechanisms of repetition‐induced summation of activity‐related pain are discussed.

Predictive equations to estimate spinal loads in symmetric lifting tasks

Response surface methodology is used to establish robust and user-friendly predictive equations that relate responses of a complex detailed trunk finite element biomechanical model to its input variables during sagittal symmetric static lifting activities. Four input variables (thorax flexion angle, lumbar/pelvis ratio, load magnitude, and load position) and four model responses (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) are considered. Full factorial design of experiments accounting for all combinations of input levels is employed. Quadratic predictive equations for the spinal loads at the L4-S1 disc mid-heights are obtained by regression analysis with adequate goodness-of-fit (R(2)>98%, p<0.05, and low root-mean-squared-error values compared with the range of predicted spine loads). Results indicate that intradiscal pressure values at the L4-L5 disc estimated based on the predictive equations are in close agreement with available in vivo data measured under similar loadings and postures. Combinations of input (posture and loading) variable levels that yield spine loads beyond the tolerance compression limit of 3400 N are identified using contour plots. Ergonomists and bioengineers, faced with the dilemma of using either complex but more accurate models on one hand or less accurate but simple models on the other hand, have thereby easy-to-use predictive equations that quantifies spinal loads and risk of injury under different occupational tasks of interest.

Assessment of the paraspinal muscles of subjects presenting an idiopathic scoliosis: an EMG pilot study.

BackgroundIt is known that the back muscles of scoliotic subjects present abnormalities in their fiber type composition. Some researchers have hypothesized that abnormal fiber composition can lead to paraspinal muscle dysfunction such as poor neuromuscular efficiency and muscle fatigue. EMG parameters were used to evaluate these impairments. The purpose of the present study was to examine the clinical potential of different EMG parameters such as amplitude (RMS) and median frequency (MF) of the power spectrum in order to assess the back muscles of patients presenting idiopathic scoliosis in terms of their neuromuscular efficiency and their muscular fatigue.MethodsL5/S1 moments during isometric efforts in extension were measured in six subjects with idiopathic scoliosis and ten healthy controls. The subjects performed three 7 s ramp contractions ranging from 0 to 100% maximum voluntary contraction (MVC) and one 30 s sustained contraction at 75% MVC. Surface EMG activity was recorded bilaterally from the paraspinal muscles at L5, L3, L1 and T10. The slope of the EMG RMS/force (neuromuscular efficiency) and MF/force (muscle composition) relationships were computed during the ramp contractions while the slope of the EMG RMS/time and MF/time relationships (muscle fatigue) were computed during the sustained contraction. Comparisons were performed between the two groups and between the left and right sides for the EMG parameters.ResultsNo significant group or side differences between the slopes of the different measures used were found at the level of the apex (around T10) of the major curve of the spine. However, a significant side difference was seen at a lower level (L3, p = 0.01) for the MF/time parameter.ConclusionThe EMG parameters used in this study could not discriminate between the back muscles of scoliotic subjects and those of control subject regarding fiber type composition, neuromuscular efficiency and muscle fatigue at the level of the apex. The results of this pilot study indicate that compensatory strategies are potentially seen at lower level of the spine with these EMG parameters.

A triaxial dynamometer to monitor lateral bending and axial rotation moments during static trunk extension efforts

OBJECTIVE The purpose of the study was to describe a new static triaxial dynamometer designed to monitor the lateral bending and axial rotation moments during trunk extension efforts. BACKGROUND Most studies on back muscle function using electromyographic spectral analysis have not controlled moments produced about the three orthopaedic axes during trunk extension efforts. Criteria to control lateral bending and axial rotation moments during extension efforts have not been proposed in the literature. METHODS Fourteen healthy subjects performed three trunk extension ramp contractions (0-100% of the maximal voluntary contraction). Triaxial L5/S1 moments at 20%, 40%, 60% and 80% of the maximal voluntary contraction in extension were extracted. RESULTS During the extension efforts, the lateral bending and axial rotation moments at L5/S1 increased significantly across the force levels and reached 6.2 Nm (SD: 6.6) and 6.1 Nm (SD: 4.5), respectively, at 80% of the maximal voluntary contraction. Tolerance limits were proposed to control these associated efforts in the context of the electromyographic analysis of back muscles. Relevance. Simultaneous measurement of lateral bending and axial rotation moments at L5/S1 during extension efforts might help to explain and control load sharing between back muscles during extension efforts.

Biomechanical analysis of a posterior transfer maneuver on a level surface in individuals with high and low-level spinal cord injuries

OBJECTIVE The purpose of this study was to determine the movement patterns and the muscular demand during a posterior transfer maneuver on a level surface in individuals with spinal cord injuries. DESIGN Six participants with high-level spinal cord injury (C7 to T6) were compared to five participants with low-level spinal cord injury (T11 to L2) with partial or complete control of abdominal musculature. BACKGROUND Developing an optimal level of independence for transfer activities figures among the rehabilitation goals of individuals with spinal cord injury. There has been no biomechanical study which specifically describes the posterior transfer maneuver. METHODS Tridimensional kinematics at the elbow, shoulder, head and trunk, as well as surface electromyographic data of the biceps, triceps, anterior deltoid, posterior deltoid, pectoralis major, latissimus dorsi, trapezius and rectus abdominus muscles were recorded during the posterior transfer. To quantify the muscular demand, the electromyographic data were amplitude normalized to the peak value obtained from maximum voluntary contractions. The transfer was divided into pre-lift, lift, and post-lift phases for analysis. RESULTS The duration of the lift phase was significantly shorter (P<0.05) for the high-level spinal cord injury (1.24; SD, 0.37 s) when compared to the low-level spinal cord injury (1.74; SD, 0.39 s). The patterns and magnitudes of the angular displacements were found similar between groups (P values: 0.45-0.98). However, the high-level spinal cord injury initiated the task from a forward flexed posture, whereas the low-level spinal cord injury adopted an almost upright alignment of the trunk. Higher muscular demands were calculated for all muscles among high-level spinal cord injury participants during the transfer when compared to the low-level spinal cord injury. However, only the anterior deltoid (high level=92.4%; low level=34.2%) and the pectoralis major (high level=109.8%; low level=25.6%) reached statistical significance during the lift phase.Conclusions. Participants with high-level spinal cord injury presented different movement characteristics and higher muscular demands during the posterior transfer than low-level spinal cord injury ones. This is probably to compensate for the additional trunk and upper limb musculature impairment. RELEVANCE The findings of this study may help to develop guidelines of specific strengthening programs for the thoracohumeral, scapulothoracic and shoulder muscles designed to restore optimal transfer capacity in individuals with spinal cord injury. Furthermore, innovative rehabilitation programs targeting the ability to control the trunk could be beneficial for these individuals.