Sue A. Ferguson

The role of dynamic three-dimensional trunk motion in occupationally-related low back disorders : the effects of workplace factors, trunk position, and trunk motion characteristics on risk of injury

Current ergonomic techniques for controlling the risk of occupationally-related low back disorder consist of static assessments of spinal loading during lifting activities. This may be problematic because several biomechanical models and epidemiologic studies suggest that the dynamic characteristics of a lift increase spine loading and the risk of occupational low back disorder. It has been difficult to include this motion information in workplace assessments because the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of low back disorder during occupational lifting in industry. More than 400 repetitive industrial lifting jobs were studied in 48 varied industries. Existing medical and injury records in these industries were examined so that specific jobs historically categorized as either high-risk or low-risk for reported occupationally-related low back disorder could be identified. A triaxial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers lifted in these high-risk or low-risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model was developed, based on biomechanical plausibility, and indicated that a combination of five trunk motion and workplace factors distinguished between high and low risk of occupationally-related low back disorder risk well (odds ratio: 10.7). These factors included 1)lifting frequency, 2) load moment, 3) trunk lateral velocity, 4) trunk twisting velocity, and 5) the trunk sagittal angle. This analysis implies that by suitably varying these five factors observed during the lift collectively, the odds of high-risk group membership may decrease by almost 11 times. The predictive power of this model was found to be more than three times greater than that of current lifting guidelines. This study though not proving causality, indicates an association between the biomechanical factors and low back disorder risk. This model could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally-related low back disorder is minimized.

Biomechanical risk factors for occupationally related low back disorders

A continuing challenge for ergonomists has been to determine quantitatively the types of trunk motion and how much trunk motion contributes to the risk of occupationally-related low back disorder (LBD). It has been difficult to include this motion information in workplace assessments since the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of LBD during occupational lifting in industry. Over 400 industrial lifting jobs were studied in 48 varied industries. The medical records in these industries were examined so that specific jobs historically categorized as either low, medium, or high risk for occupationally-related LBD could be identified. A tri-axial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers worked at these low, medium, or high risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model indicated that a combination of five trunk motion and workplace factors predicted well both medium risk and high risk occupational-related LBD. These factors included lifting frequency, load moment, trunk lateral velocity, trunk twisting velocity, and trunk sagittal angle. Increases in the magnitude of these factors significantly increased the risk of LBD. The analyses have enabled us to determine the LBD risk associated with combined changes in the magnitudes of the five factors. The results indicate that by suitably varying these five factors observed during the lift collectively, the odds of high risk group membership may decrease by over ten times. These results were related to the biomechanical, ergonomic, and epidemiologic literature. The five trunk motion and workplace factors could be used as quantitative, objective measures to redesign the workplace so that the risk of occupationally-related LBD is minimized.

Spine loading characteristics of patients with low back pain compared with asymptomatic individuals.

Study Design. Patients with low back pain and asymptomatic individuals were evaluated while performing controlled and free-dynamic lifting tasks in a laboratory setting. Objective. To evaluate how low back pain influences spine loading during lifting tasks. Summary of Background Data. An important, yet unresolved, issue associated with low back pain is whether patients with low back pain experience spine loading that differs from that of individuals who are asymptomatic for low back pain. This is important to understand because excessive spine loading is suspected of accelerating disc degeneration in those whose spines are damaged already. Methods. In this study, 22 patients with low back pain and 22 asymptomatic individuals performed controlled and free-dynamic exertions. Trunk muscle activity, trunk kinematics, and trunk kinetics were used to evaluate three- dimensional spine loading using an electromyography- assisted model in conjunction with a new electromyographic calibration procedure. Results. Patients with low back pain experienced 26% greater spine compression and 75% greater lateral shear (normalized to moment) than the asymptomatic group during the controlled exertions. The increased spine loading resulted from muscle coactivation. When permitted to move freely, the patients with low back pain compensated kinematically in an attempt to minimize external moment exposure. Increased muscle coactivation and greater body mass resulted in significantly increased absolute spine loading for the patients with low back pain, especially when lifting from low vertical heights. Conclusions. The findings suggest a significant mechanical spine loading cost is associated with low back pain resulting from trunk muscle coactivation. This loading is further exacerbated by the increases in body weight that often accompany low back pain. Patient weight control and proper workplace design can minimize the additional spine loading associated with low back pain.

The classification of anatomic- and symptom-based low back disorders using motion measure models

Study Design This study observed the trunk angular motion features of healthy subjects and those experiencing chronic low back disorders as they flexed and extanded their trunks in five symmetric and asymmetric planes of motion. Trunk angular positon, velocity, and acceleration were evaluated during several cycles of motion. Objective The trunk angular motion features of the low back disorder group were normalized relative to the healthy subjects and used to 1) evaluate the repeat-ability and reilability of trunk motion as a measure of trunk musculoskeletal status, 2) quantify the extent of the disorder, 3) determine the extent to which trunk motion measures might be used as quantifiable means to help classify low back disorders. Summary of Background Data Given the magnitude of the low back disorder problem, it is problematic that there are few quantitative methods for objectively documenting the extent of a disorder Impairment ratings of low back disorders can very by as much as 70% using current systems. Diagnoses and classification schemes are rarely based upon quantitative indicators and we are unable to easily assess and diagnose low back disorders so that proper treatment can be administered and the risk of exacerbating the problem can be minimized. Methods Three-hundred-thirty-nine men and women between 20 and 70 years old who had not experienced significant back pain were recruited as the healthy subjects in this study. One hundred-seventy one patients with various chronic low back disorders also were recruited and compared with the healthy group of subjects. All subjects wore a triaxial goniometar on their trunks that documented the angular position velocity, and acceleration of the trunk as the subjects flexed and extended their trunks in each of five planes of motion. Trunk motion features first were normalized for subject gender and age. Several two-stage eight-variable models that account for trunk motion interactions were developed to classify the 510 healthy and low back-injured subjects into one of 10 anatomic and sympton-based low back disorder classification categories. Results Using conservative cross-validation measures, it was found that the stage one eigth-variable model could correctly classify more than 94% of the subjects as either healthy or having a low back disorder. One of the stage two eight-variable models was able to reasonably classify the patients with low back disorders into one of 10 low back disorder classification groups. Conclusion The motion-related parameters may relate to biomechanical or learned sensitivities to spinal loading. This study suggests that higher-order trunk motion characteristics hold great promise as a quantitative indicator of the trunks musculoskeletal status and may be used as a measure of the extent of a disorder and as a measure of rehabilitative progress. Further more, once the interactive nature of these trunk motion characteristics is considered, the model could help diagnose low back disorders. However, independent data sets are needed to validate these findigs.

The quantification of low back disorder using motion measures : Methodology and validation

STUDY DESIGN Trunk angular motion features were used as a means to quantify the extent of a low back disorder in healthy people and patients with chronic low back disorders. OBJECTIVE To refine and validate a previously reported means of quantifying the extent of a low back disorder. SUMMARY AND BACKGROUND Many assessment tools of low back disorder are subjective. A quantitative assessment tool would facilitate the tracking of the recovery and help document the appropriateness of treatments. METHODS The trunk motion characteristics of 374 healthy people and 335 patients with chronic low back disorders of varying severity were documented as they flexed and extended their trunks in five different planes of motion. The trunk motion features were normalized as a function of age and gender. Four classification techniques were used to assess the ability of the quantitative motion measure to identify those with and without low back disorders. In addition, 31 patients were observed longitudinally to determine whether the motion measures agreed with observed changes in back pain symptoms. RESULTS The quantitative trunk motion measure distinguished between people with low back disorders and healthy people between 88% and 94% of the time, depending on which classification system was used. Sensitivity and specificity varied between 83% and 97%. The quantitative measure also showed promise as a means to distinguish between muscle-based and structure-based low back disorders. Prospective findings indicated that the quantification system agreed well with clinical observations of progress. CONCLUSIONS The quantification of trunk motion can serve as a measure of the extent of a low back disorder. When considered along with other clinical information, the ability to assess and treat low back disorders is enhanced.

The effectiveness of commonly used lifting assessment methods to identify industrial jobs associated with elevated risk of low-back disorders

Low-back disorders (LBD) continue to be the most costly and common musculoskeletal problem facing society today. Investigators have developed tools or measures that are intended to identify jobs that will probably be associated with an elevated risk of low-back disorders. However, an important and not widely discussed issue associated with these tools and procedures has been that of the validity or effectiveness of the tools. Therefore the objective of this study was to evaluate the validity and effectiveness of two commonly used types of LBD assessment methods in terms of their ability to correctly associate jobs with LBD risk. The 1981 NIOSH Work Practices Guide for Manual Lifting and the 1991 NIOSH revised lifting equation, along with psychophysical measures were assessed for their ability to correctly identify high-, medium-, and low-risk (of LBD) jobs. Risk was defined according to a database of 353 industrial jobs representing over 21 million person-hours of exposure. The results indicated that both NIOSH measures were predictive and resulted in odds ratios between 3.1 and 4.6. Higher odds ratios were found when the maximum horizontal distance was used to assess a job compared to the average horizontal distance. Further analyses indicated that the two NIOSH assessment methods classified risk in very different ways. The 1981 NIOSH Guide demonstrated good specificity (91%) in that it identified low-risk jobs well but it also displayed low sensitivity by only correctly identifying 10% of the high-risk jobs. The 1993 NIOSH revised lifting equation, on the other hand, had better sensitivity. It correctly identified 73% of the high-risk jobs but did not identify low- and medium-risk jobs well. Using psychophysical criteria it was observed that 60% of the high-risk jobs would be judged to be acceptable, whereas, 64% and 91% of the medium- and low-risk jobs, respectively, would be judged to be acceptable. This study indicates that the different measures have various strengths and weaknesses. When controlling for occupational LBD it should be recognized that a variety of measures exist and that the measure that most appropriately assesses risk depends upon the characteristics of the job.

Spine loading in patients with low back pain during asymmetric lifting exertions

BACKGROUND CONTEXT Recurrent low back pain (LBP) is a common and costly problem that might be related to increased spine loads in those with LBP. However, we know little about how the spine is loaded when those with LBP perform lifting exertions. PURPOSE Document spine loading patterns of patients with LBP performing symmetric and asymmetric lifting exertions compared with asymptomatic individuals performing the same tasks. STUDY DESIGN Spine loadings during lifting exertions that varied in asymmetric origin as well as horizontal and vertical distance from the spine were compared between asymptomatic subjects and patients with LBP. METHODS Sixty-two patients with LBP and 61 asymptomatic individuals performed a variety of lifting exertions that varied in lift origin horizontal and vertical position (region), lift asymmetry position and weight lifted. An electromyography-assisted model was used to evaluate spine loading in each subject during the lifting exertions. Differences in spine loading between the LBP and asymptomatic subjects were noted as a function of the experimental variables. RESULTS Patients with LBP experienced greater spine compression and shear forces when performing lifting tasks compared with asymptomatic individuals. The least taxing conditions resulted in some of the greatest differences between LBP and asymptomatic individuals. CONCLUSIONS Greater levels of antagonistic muscle coactivation resulted in increases in spine loading for patients with LBP. Specific lifting conditions that tend to exacerbate loading can be identified by means of physical workplace requirements. These findings may impact acceptable return-to-work conditions for those with LBP.

Low back pain recurrence in occupational environments.

Study Design. Prospective assessment of return to work after low back pain. Objective. To determine which factors or combination of factors best predict recurrence of low back pain (defined 4 different ways) when returning to full-duty work. Summary of Background Data. Recurrent back pain is one of the more costly health problems facing industry today. Few systematic evaluations of the various factors suspected of exacerbating low back pain have been reported in the literature. Methods. A total of 206 workers who reported low back pain were evaluated as they returned to full-duty work. Five types of assessments were performed including: 1) a low back kinematic functional assessments, 2) evaluation of job physical demands, 3) psychosocial assessment of the job environment, 4) self-reported impairment including perception of symptoms and psychological measures, and 5) personal (individual) factors. One year after return to full duty workers were interviewed to assess who had a recurrence of low back pain according to 4 different definitions of low back pain (symptom reports, medical visits, self-reported lost days, and employer-reported lost days due to back pain). Multiple logistic regression models were developed to assess the best combinations of predictors. Results. The most liberal definition of recurrence, recurrent symptoms, had a significantly greater recurrence rate at 58% than all other outcome measures (P = 0.0001). The medical visit recurrence rate of 36% was significantly greater than the more conservative lost time measures (P = 0.0001). The recurrence rate for self-reported lost time was 15%, whereas the more conservative employer confirmed lost time measure was significantly lower at 10% (P = 0.0077). Multivariate predictive models associated with the various recurrence definitions yielded sensitivities varying between 78% and 80% and specificity between 73% and 80%. Conclusion. Recurrence is greatly dependent on how one defines recurrence with symptom reporting yielding 5.5 times as many recurrences compared with employer confirmed lost time. In general, more quantitative measures of worker musculoskeletal function yielded the best predictions of recurrence when predicting the more restrictive definitions of recurrence (employer confirmed lost time).

Lumbar spine forces during manoeuvring of ceiling-based and floor-based patient transfer devices

Patient handling continues to represent a high risk task for low back pain (LBP) among health caregivers. Previous studies indicated that manual transfers of patients impose unacceptable loads on the spine even when two caregivers perform the transfer. Patient lift devices are considered a potential intervention; however, few biomechanical analyses have investigated the spine loads and LBP risk associated with these transfer devices. This study analysed the 3-D spine forces imposed upon the lumbar spine when 10 subjects manipulated ceiling-based and floor-based patient lifts through various patient handling conditions and manoeuvres. The results indicated that ceiling-mounted patient lift systems imposed spine forces upon the lumbar spine that would be considered safe, whereas floor-based patient handling systems had the potential to increase anterior/posterior shear forces to unacceptable levels during patient handling manoeuvres. Given these findings, ceiling-based lifts are preferable to floor-based patient transfer systems.

Longitudinal quantitative measures of the natural course of low back pain recovery.

Study Design. A prospective study was developed to quantify acute low back pain recovery. Objective. To compare traditional self-report measures of low back pain recovery with a quantitative measure of recovery. Summary of Background Data. The magnitude of low back disorders in society continues to be a problem. To prevent secondary injuries, an understanding of recovery must be gained by comparing the natural course of recovery using several outcome measures. Methods. For this study, 16 occupational and 16 nonoccupational patients with low back pain were recruited. Recovery was monitored prospectively every 2 weeks for 3 to 6 months, using subjective work status, pain symptoms, activities of daily living, and objective functional performance probability (trunk kinematics). Results. Return to work underestimated the percentage of subjects impaired, as compared with all other outcome measures. Symptoms, activities of daily living, and functional performance probability all showed similar patterns of recovery for 0 to 12 weeks. At 14 weeks, there was a lag in functional performance recovery. Both symptoms and activities of daily living indicated that 80% of the population was recovered, whereas functional performance indicated the figure to be 68%. Conclusion. This prospective study demonstrates the natural course of recovery using several outcome measures. The objective kinematic functional performance measure of recovery quantifies a different aspect of impairment not evaluated by traditional subjective measures. Use of several outcome measures may lead to a better understanding of low back pain recovery or residual impairment, which may minimize the risk of recurrent injury.