Work disability prevention research: current and future prospects.

Work disability prevention has evolved from being a component of disease outcomes studies, to a separate and growing research discipline. In part, this is due to recognition that work outcomes often do not correlate with other health outcomes; the causes of work disability are multiple, complex, and often distinct from associated health conditions or treatments; and that work disability creates an important personal, economic and social burden that is often preventable. Conceptual frameworks, measures, research methods and interventions specific to this area have been developed, many have been validated across different contexts, and an international community of researchers and trainees in work disability prevention has formed. The articles included in this special section exemplify the breadth of current research in this field, and future opportunities for greater cross- disciplinary collaboration and translation of research to practical implementation and policy interventions.

Can cross country differences in return-to-work after chronic occupational back pain be explained? An exploratory analysis on disability policies in a six country cohort study.

INTRODUCTION: There are substantial differences in the number of disability benefits for occupational low back pain (LBP) among countries. There are also large cross country differences in disability policies. According to the Organization for Economic Cooperation and Development (OECD) there are two principal policy approaches: countries which have an emphasis on a compensation policy approach or countries with an emphasis on an reintegration policy approach. The International Social Security Association initiated this study to explain differences in return-to-work (RTW) among claimants with long term sick leave due to LBP between countries with a special focus on the effect of different disability policies. METHODS: A multinational cohort of 2,825 compensation claimants off work for 3-4 months due to LBP was recruited in Denmark, Germany, Israel, the Netherlands, Sweden, and the United States. Relevant predictors and interventions were measured at 3 months, one and 2 years after the start of sick leave. The main outcome measure was duration until sustainable RTW (i.e. working after 2 years). Multivariate analyses were conducted to explain differences in sustainable RTW between countries and to explore the effect of different disability policies. RESULTS: Medical and work interventions varied considerably between countries. Sustainable RTW ranged from 22% in the German cohort up to 62% in the Dutch cohort after 2 years of follow-up. Work interventions and job characteristics contributed most to these differences. Patient health, medical interventions and patient characteristics were less important. In addition, cross-country differences in eligibility criteria for entitlement to long-term and/or partial disability benefits contributed to the observed differences in sustainable RTW rates: less strict criteria are more effective. The model including various compensation policy variables explained 48% of the variance. CONCLUSIONS: Large cross-country differences in sustainable RTW after chronic LBP are mainly explained by cross-country differences in applied work interventions. Differences in eligibility criteria for long term disability benefits contributed also to the differences in RTW. This study supports OECD policy recommendations: Individual packages of work interventions and flexible (partial) disability benefits adapted to the individual needs and capacities are important for preventing work disability due to LBP.

Margin of manoeuvre indicators in the workplace during the rehabilitation process: a qualitative analysis.

INTRODUCTION: The task of evaluating workers' capacity to return to their pre-injury employment or other jobs continues to pose a daily challenge for clinicians. In this study, a concept frequently used in the field of ergonomics, the margin of manoeuvre (MM), was applied during the rehabilitation process. The study identified the indicators of the MM taken into account during the return to work of workers with musculoskeletal disorders. METHODS: This study used a multiple-case design. A case was defined as a dyad comprising a worker admitted to a work rehabilitation program and the clinician who was managing the return-to-work process. The results were then validated with investigators and expert ergonomists, through group interviews. Content analyses were performed using the conceptual framework for the work activity model adapted from Vézina and the procedures recommended by Miles and Huberman. RESULTS: A total of 11 workers, five clinicians, two experts and two investigators participated in this study. The interview analysis process resulted in a more detailed definition of the MM and the identification of 50 indicators. The indicators were classified according to six dimensions: (1) work context; (2) employer's requirements and expectations; (3) means and tools; (4) worker's personal parameters; (5) work activity; and (6) impacts of the work situation. CONCLUSIONS: The more specific indicators identified in this study will allow for more systematic observation of the MM. Subsequent studies will seek to link each indicator described in the model with a specific method of observation.

Workplace interventions for workers with musculoskeletal disabilities: a descriptive review of content.

BACKGROUND: Despite the convergence of scientific data to the effect that interventions in the workplace promote a healthy return to work, the interventions carried out in the real work environment appear to be very heterogeneous and ill-defined. OBJECTIVE: The goal of this review is to identify the different objectives pursued through the workplace interventions carried out in the context of a rehabilitation program, and to describe the activities involved. METHODS: A descriptive review of the literature, including various research designs, was carried out. RESULTS: This review reveals great heterogeneity in the content of interventions offered in the workplace to workers with musculoskeletal disabilities. The objectives of workplace interventions may range from gathering information in order to reproduce work demands in a clinical setting, to gradually exposing workers to the demands of the real work environment, or permanently reducing the demands of the work situation. A descriptive analysis of the literature also brings to light the diversity of actions carried out, human resources used, and workplace environments involved, while highlighting the few documented process outcome evaluations that have been done of workplace interventions. CONCLUSION: It is recommended that in future research in this area, efforts be made to better describe the components of the interventions, to develop process outcomes representing the multidimensional results obtained in the workplace, and to differentiate between temporary and permanent modifications made to the work situation.

Measurement properties of a new quality of life measure for patients with work disability associated with musculoskeletal pain.

INTRODUCTION: The Quality of Life Systemic Inventory (QLSI) measures patients' goal attainment based on the system control theory. It quantifies the perceived impact of the disorder and the gap between the present and aspired states. PURPOSE: To evaluate concurrent validity and responsiveness of the QLSI among workers on sick leave due to musculoskeletal disorders (MSDs). METHODS: Participants (10 women; 29 men) were recruited at a work rehabilitation centre and had more than 4 weeks of absence from work due to MSDs compensated by the Workers' Compensation Board. Concurrent validity and external responsiveness were based on baseline and post-treatment measures of external criteria. Criteria and related instruments were the following: perception of disability (Roland-Morris Disability Questionnaire); health-related quality of life (SF-12); stress (Psychological Stress Measure) and distress (Psychological Distress Index). RESULTS: Regression analyses revealed significant correlations between QLSI scores and the Psychological Distress Index (r2 = .11 to .19 and .66; p < .001), with either the SF-12 mental component scale (r2 = .18 and .11; p < .01) or the Roland-Morris Disability Questionnaire (r2 = .04 and .10; p < .05). All measures showed highly significant change over time. CONCLUSION: Results support the concurrent validity and responsiveness of the QLSI, with an MSD population. SIGNIFICANCE: This instrument could serve in future research as an outcome measurement instrument in the evaluation of more long-term effects of rehabilitation programs.

[Effectiveness of interventions for low-back-pain sufferers: the return to work criterion]. / Efficacité des interventions s'adressant à des sujets lombalgiques, du point de vue du retour au travail.

BACKGROUND: Return to work is considered as a major effectiveness criterion for interventions dedicated to subacute or chronic low-back-pain sufferers. Moreover, return to work, beyond the economic and social Issues, is regarded more and more as having a therapeutic dimension. This review aims to describe the various interventions which are effective in returning patients to work. METHODS: The presentation is based on existing reviews supplemented by a selection of recent studies. RESULTS: "Cognitive-behavioral therapy", "reassurance" and "back exercises" are some suggested approaches. Some of these techniques are geared specifically towards work. Others, such as "back schools" or "multidisciplinary interventions" combine different approaches. CONCLUSION: Promoting return to work at an appropriate stage (subacute stage) could help low-back-pain sufferers to avoid prolonged disability.

Cost-benefit and cost-effectiveness analysis of a disability prevention model for back pain management: a six year follow up study.

AIMS: To test the long term cost-benefit and cost-effectiveness of the Sherbrooke model of management of subacute occupational back pain, combining an occupational and a clinical rehabilitation intervention. METHODS: A randomised trial design with four arms was used: standard care, occupational arm, clinical arm, and Sherbrooke model arm (combined occupational and clinical interventions). From the Quebec WCB perspective, a cost-benefit (amount of consequence of disease costs saved) and cost-effectiveness analysis (amount of dollars spent for each saved day on full benefits) were calculated for each experimental arm of the study, compared to standard care. RESULTS: At the mean follow up of 6.4 years, all experimental study arms showed a trend towards cost benefit and cost effectiveness. These results were owing to a small number of very costly cases. The largest number of days saved from benefits was in the Sherbrooke model arm. CONCLUSIONS: A fully integrated disability prevention model for occupational back pain appeared to be cost beneficial for the workers' compensation board and to save more days on benefits than usual care or partial interventions. A limited number of cases were responsible for most of the long term disability costs, in accordance with occupational back pain epidemiology. However, further studies with larger samples will be necessary to confirm these results.

Evaluation of measurement strategies to increase the reliability of EMG indices to assess back muscle fatigue and recovery.

The purpose of this study was to assess different measurement strategies to increase the reliability of different electromyographic (EMG) indices developed for the assessment of back muscle impairments. Forty male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three sessions at least 2 days apart within 2 weeks. Surface EMG signals were recorded from four pairs (bilaterally) of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10) while the subjects performed, in a static dynamometer, two static trunk extension tasks at 75% of the maximal voluntary contraction separated by a 60 s rest period: (1) a 30 s fatigue task and (2) a 5 s recovery task. Different EMG indices (based on individual muscles or averaged across bilateral homologous muscles or across all muscles) were computed to evaluate muscular fatigue and recovery. Intra-class correlation coefficient (ICC) and standard error of measurement (SEM) in percentage of the grand mean were calculated for each EMG variable. Reliable EMG indices are achieved for both healthy and chronic low back pain subjects when (1) electrodes are positioned on medial back muscles (multifidus at the L5 level and longissimus at L1) and (2) measures are averaged across bilateral muscles and/or across two fatigue tests performed within a session. The most reliable EMG indices were the bilateral average of medial back muscles (ICC range: 0.68-0.91; SEM range: 5-35%) and the average of all back muscles (ICC range: 0.77-0.91; SEM range: 5-30%). The averaging of measures across two fatigue tests is predicted to increase the reliability by about 13%. With regards to EMG indices of fatigue, the identification of the most fatigable muscle also lead to satisfactory results (ICC range: 0.74-0.79; SEM range: 21-26%). The assessment of back muscle impairments through EMG analysis necessitates the use of multiple electrodes to achieve reliable results.

Effect of step and ramp static contractions on the median frequency of electromyograms of back muscles in humans.

The purpose of this study was to compare the electromyogram median frequency (MF) values from two contraction modes (ramp vs step) at different force levels of eight back muscles. A group of 20 healthy male subjects stood in a dynamometer with the trunk in a vertical position and performed trunk extension contractions using the displayed L5/S1 extension moment as visual feedback. The electromyogram (EMG) signals from four pairs of back muscles were collected at 4,096 Hz using active surface electrodes during two 7 s static ramp contractions ranging from 0% to 100% of the maximal voluntary contraction (MVC) and two 5 s static step contractions performed at five forces (10%, 20%, 40%, 60% and 80% MVC). The root mean square (RMS) and MF of the EMG signals corresponding to 250 ms windows were computed at each force level for both contraction modes. The RMS from the ramp contractions were significantly higher than from the step contractions in six muscles. The corresponding MF showed a significant (alpha = 0.05) contraction mode x force interaction in four muscles. A significant contraction mode main effect was obtained in four muscles having higher MF during step than during ramp contractions. These differences were more obvious (10-15 Hz) and more frequent at the lower (10%, 20% and 40% MVC) forces. It was suggested that mechanisms not related to motor unit recruitment might influence MF in contraction modes. These unknown mechanisms contaminate any possible relationship between the MF measurements and muscle composition.

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.

Implementation of a participatory ergonomics program in the rehabilitation of workers suffering from subacute back pain.

This paper describes a participatory ergonomics program aimed at early return to regular work of workers suffering from subacute occupational back pain and assesses the perceptions of the participants on the implementation of ergonomic solutions in the workplace. The participatory ergonomics program was used in the rehabilitation of workers suffering from subacute back pain for more than 6 weeks, a program that was associated with an increased rate of return to work. The perceptions of the participatory ergonomics participants were assessed 6 months after completion of the ergonomic intervention through a questionnaire sent to employer representatives, union representatives and injured workers of participating workplaces. About half of the ergonomic solutions were implemented according to the perception of the participants, with a substantial agreement between respondents.

Median frequency of the electromyographic signal: effect of time-window location on brief step contractions.

The purpose of this study was to determine, for different back muscles, if the median frequency (MF) of the electromyographic (EMG) power spectrum changes according to the position of the time window during a 5 s step contraction. Twenty males with no known back problems were standing upright in a dynamometer allowing lower limb and pelvis stabilization. Trunk extension efforts were performed by pushing on a force platform positioned at the T4 level while the extension moment at L5/S1 was displayed as visual feedback. The EMG signals from four homologous back muscles (multifidus at L5, ilicostalis lumborum at L3, and longissimus at L1 and T10) were collected using active surface electrodes during two 5 s static step contractions performed at five force levels (10, 20, 40, 60 and 80% of the maximal voluntary contraction). The root mean square (RMS) and MF values of the EMG signals corresponding to three 250 ms time windows (beginning, middle and end of each step contraction) were computed. The RMS values of several back muscles increased from the first to the third time window for contractions performed at high force levels only. However, a concomitant decrease in the MF values was observed only for the left multifidus muscle. It was concluded that muscle fatigue does not generally manifest itself during 5 s step contractions through the EMG signal. However, it is recommended to use step contractions lasting less than 5 s and to choose a time window located in the first 1-3 s to completely eliminate the possible effects of fatigue.

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.

Physical impairments in cervicogenic headache: traumatic vs. nontraumatic onset.

In order to quantify the physical impairments associated with different types of headache, 77 subjects belonging to four different groups (postmotor vehicle accident cervicogenic headache subjects, cervicogenic headache subjects nontraumatic, migraine patients and control subjects) were evaluated using the following variables: posture, cervical range of motion, strength of the neck flexors and extensors, endurance of the short neck flexors, manual segmental mobility, proprioception of the neck, and pain (McGill Pain Questionnaire and the skin roll test). The results of this study showed that postmotor vehicle accident cervicogenic patients have significantly limited active cervical range of motion (in flexion/extension and rotations), present decreased strength and endurance of neck flexors and decreased strength of the extensor muscles. Our results suggest that there are enough differences between the postmotor vehicle accident and nontraumatic cervicogenic headache subjects to warrant caution when analysing the data of these two subgroups together, as several studies have done in the past. The onset of headache is therefore an important variable that should be controlled for when attempting to characterize the physical impairments associated with cervicogenic headache.

Disability measurement in persons with back pain: a validity study of spinal range of motion and velocity.

OBJECTIVE: To evaluate the criterion validity and responsiveness to change of spine kinematic variables to assess disability in patients with low back pain. DESIGN: Blinded comparison between spine kinematic variables, Oswestry disability questionnaire scores, and work status. SETTING: Multidisciplinary occupational rehabilitation clinic of a university hospital. PATIENTS: Population-based cohort of 111 patients with subacute work-related back pain who were absent from regular work for more than 4 weeks because of back pain. INTERVENTIONS: This study was part of a population-based randomized clinical trial. Patients were randomized to 4 different methods of management: usual care, rehabilitation, ergonomics, or rehabilitation and ergonomics. MAIN OUTCOME MEASURES: Oswestry disability questionnaire, kinematic analysis of the spine during flexion and extension of the trunk, and work status were collected at weeks 4, 12, 24, and 52 after the back accident. RESULTS: Kinematic variables were poorly to moderately related to work status and Oswestry questionnaire scores. Kinematic variables were also unresponsive to change in work status and Oswestry questionnaire scores over time. CONCLUSION: Spine kinematics during flexion and extension of the trunk do not appear to be a valid measure of disability in patients with subacute and chronic back pain.

An application of pattern recognition for the comparison of trunk muscles EMG waveforms between subjects with and without chronic low back pain during flexion-extension and lateral bending tasks.

The purpose of the study was twofold: (1) to evaluate the reliability of distance measures computed from a principal component analysis (PCA) of electromyographic (EMG) waveforms of trunk muscles recorded during standardized trunk movements and (2) to evaluate their sensitivity to the load lifted, the trunk range of motion (ROM) and to low back status. Thirty-three male subjects (18 normals, 15 suffering from non specific CLBP) aged between 35-45 years participated. The EMG signals from 12 trunk muscles and the kinematics of trunk segments were recorded during 12 tasks. The subjects performed flexion-extension and lateral bending (left and right) tasks (three complete cycles) with and without a 12 kg load and at different trunk ROM (maximal or at defined submaximal angles). Distance measures locating each subject relative to a reference PCA model were computed for each muscle and task. The reliability of these distance measures was evaluated for 10 subjects (five normals and five CLBP) who performed two tasks on three different days. The reliability of distance measures was acceptable for agonist muscles only. The distance measures were sensitive to the load lifted and to the trunk ROM for different muscles and tasks but poorly sensitive to low back status. Several reasons that could explain the low sensitivity of these measures to low back status are discussed and potential solutions are proposed. A procedure based on a reliability analysis is proposed to select the number of principal components to include in the reference PCA model. It is expected that the refinement of the method used in this study could provide an effective clinical tool to assess EMG waveforms of trunk muscles during dynamic tasks.

The effect of load on the coordination of the trunk for subjects with and without chronic low back pain during flexion-extension and lateral bending tasks.

OBJECTIVE: To evaluate if patients move their trunk sections differently than normal subjects and to determine if these differences increase when lifting a load. DESIGN: Comparative study using a repeated measures design. BACKGROUND: Many studies demonstrate a modification of the lumbar-pelvic rhythm for chronic low back pain patients but the large variability of the results impair the discrimination power. It was hypothesized that the lifting of a load would magnify the manifestation of lumbar impairments. METHODS: Fifteen chronic low back pain patients and 18 normal subjects performed maximal flexion-extension and lateral bending of the trunk with and without a 12 kg load. The pelvic, lumbar and thoracic motions were measured with a motion analysis system. RESULTS: During flexion-extension tasks, a significant decrease in lumbar flexion and increase in thoracic flexion were observed for the patients. The load effect was significant for all trunk sections but did not allow a better discrimination between groups. CONCLUSIONS: Lifting a 12 kg load during flexion-extension of the trunk did confirm alteration in trunk section coordination but did not help to better discriminate patients from normal subjects. However, it was demonstrated for the first time that chronic low back pain patients compensate for a loss of lumbar flexion by increasing their thoracic flexion. RELEVANCE: The lumbar-pelvic rhythm is routinely used to evaluate low back impairments. The use of kinematic measures enhance the objectivity of the examination but the large variability of the results impair the discrimination power. Lifting a load during such an evaluation might magnify the low back impairments and increase the discrimination power of this measure.

The comparison of trunk muscles EMG activation between subjects with and without chronic low back pain during flexion-extension and lateral bending tasks.

The purpose of the study was to compare the electromyographic (EMG) activity of the trunk muscles between normal subjects and chronic low back pain (CLBP) patients during standardized trunk movements. Thirty-three male subjects (18 normals, 15 suffering from non specific CLBP) aged between 35 and 45 yr participated. A biomechanical analysis involving the recording of EMG signals from 12 trunk muscles, the kinematics of trunk segments and the computation of L5/S1 moments was performed. The subjects performed flexion-extension and lateral bending (left and right) tasks (three complete cycles) with and without a 12 kg load. Between group comparisons were performed on the full cycle average pattern of all biomechanical variables for each task. The reliability of EMG variables was evaluated for 10 subjects (5 normals and 5 CLBP) who performed the tasks on three different days. The reliability of EMG amplitude values was generally excellent for agonist muscles but poor to moderate for antagonists. The EMG amplitude analysis revealed significant differences between groups for some muscles (left lumbar and thoracic erector spinae). The abnormal (asymmetric) EMG patterns detected among CLBP patients were not explained by postural asymmetries.

Is work status of low back pain patients best described by an automated device or by a questionnaire?

STUDY DESIGN: A prospective cohort study of patients with subacute occupational back pain. OBJECTIVES: To study the relation between a marketed opto-electric device measuring trunk kinematics, a widely used specific functional capacity questionnaire, and work status in back pain patients, and to assess the responsiveness to change in work status of the opto-electric device and the questionnaire. SUMMARY OF BACKGROUND DATA: Several instruments have been developed to evaluate the functional capacities of patients with back pain, but the relation between these instruments and work status has rarely been studied. METHODS: The relation between the opto-electric device, the questionnaire, and work status in patients with back pain was evaluated. The study population was a prospective cohort of patients with subacute back pain who were absent from regular work for more than 4 weeks. All data were compiled blindly on the same day, at study entry (4 weeks after work accident), and at 12, 24, and 52 weeks after the work accident. The validity of the questionnaire and opto-electric device scores was assessed with partial correlation analyses, standardized response mean, logistic regression analyses, and receiver operating characteristics curves. RESULTS: The correlation between the questionnaire and opto-electric device scores was low. The questionnaire scores were significantly related to work status, but the opto-electric device scores were not. The questionnaire was responsive to change in work status, whereas the opto-electric device was not. CONCLUSIONS: The opto-electric device scores were not related to either functional capacity scores (questionnaire) or work status in patients with low back pain, and the opto-electric device was not responsive to change in work status. Conversely, the questionnaire was related to work status and was responsive to change in work status.