Deborah Burr

Gender differences in prevalence of upper extremity musculoskeletal disorders.

A literature review was conducted on the current literature base to determine the strength of support for the hypothesis that women experience higher prevalences of upper extremity musculoskeletal disorders (UEMSDs) than men. Fifty-six articles were reviewed for data on gender differences in frequency, incidence or prevalence rates for musculoskeletal disorders specific to the upper extremities. These articles included both general and working populations. The majority of the studies showed that women had significantly higher incidences of various types of UEMSDs than men. This trend was consistently observed in studies based on self-report or plant/workers compensation records, with and without physical examination, and after adjusting for potential confounders such as age and physical work factors. With men as the referent, the odds ratio (OR) or prevalence ratio (PR) for UEMSDs ranged from 0.85 to 10.05 for self report. For self report combined with physical examination, the OR/PR ranged from 0.66 to 11.4. The OR/PR for carpal tunnel syndrome (CTS) ranged from 0.6 to 2.87 with confounder adjustment. These findings suggest that women do have significantly higher prevalences than men for many types of UEMSDs, even after controlling for the type of data source and confounders such as age or work factors.

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).

Torso flexion loads and the fatigue failure of human lumbosacral motion segments

Study Design. Spine loads associated with lifting a 9-kg weight were estimated at three torso flexion angles (0°, 22.5°, and 45°), and lumbosacral motion segments were cyclically loaded using these loads until failure or to a maximum of 10,020 cycles. Objectives. To simulate the postures and loads experienced by the lumbar spine during repetitive lifting of moderate weights in different torso flexion postures, and to analyze the fatigue failure response of lumbosacral motion segments. Summary of Background Data. Previous fatigue failure studies of lumbar motion segments have not reproduced the combination of spinal postures, loads, and load rates anticipated in different torso flexion postures during lifting tasks characteristic of those in occupational settings. Methods. Twelve fresh human lumbosacral spines were dissected into three motion segments each (L1–L2, L3–L4, and L5–S1). Motion segments within each spine were randomly assigned to a simulated torso flexion angle (0°, 22.5°, or 45°) using a partially balanced incomplete block experimental design. Spinal load and load rate were determined for each torso flexion angle using previously collected data from an EMG-assisted biomechanical model. Motion segments were creep loaded for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). Specimens were inspected to determine failure mechanisms. Results. The degree of torso flexion had a dramatic impact on cycles to failure. Motion segments experiencing the 0° torso flexion condition averaged 8,253 cycles to failure (±2,895), while the 22.5° torso flexion angle averaged 3,257 (±4,443) cycles to failure, and motion segments at the 45° torso flexion angle lasted only 263 cycles(±646), on average. The difference was significant at P < 0.0001, and torso flexion accounted for 50% of the total variance in cycles to failure. Conclusions. Fatigue failure of spinal tissues can occur rapidly when the torso is fully flexed during occupational lifting tasks; however, many thousands of cycles canbe tolerated in a neutral posture. Future lifting recommendations should be sensitive to rapid development of fatigue failure in torso flexion.

Measuring trunk motions in industry: variability due to task factors, individual differences, and the amount of data collected.

The focus of this study was to determine the amount of data needed to ensure sufficient accuracy in estimating mean trunk motions of employees performing industrial manual materials handling tasks. Over 450 tasks were selected, in which the load weight and the vertical start and destination heights of the activity remained constant throughout the task. Data were collected as employees did their work at the job site, using the Lumbar Motion Monitor. Variance components were estimated in a hierarchical design and used to compute standard errors of mean trunk kinematic measures. These analyses found task-to-task variation to be much larger than the variability due to either multiple employees performing the same task or to repetitive movements within a task. Also, it was found that no significant reduction in the standard errors occurred when data were gathered for more than three employees and three repetitions of each task by an employee. This study indicates that the vast majority of variability in mean trunk motions is accounted for by the design of work tasks, and variations due to repeated cycles of a task or to employees are rather minor. It is also important as a basis for future work on modelling low-back disorder risk based on a jobs trunk kinematic measures.

Smoking, environmental tobacco smoke, and risk of renal cell cancer: a population-based case-control study

BackgroundKidney and renal pelvis cancers account for 4% of all new cancer cases in the United States, among which 85% are renal cell carcinomas (RCC). While cigarette smoking is an established risk factor for RCC, little is known about the contribution of environmental tobacco smoke (ETS) to RCC incidence. This study assesses the role of smoking and ETS on RCC incidence using a population-based case-control design in Florida and Georgia.MethodsIncident cases (n = 335) were identified from hospital records and the Florida cancer registry, and population controls (n = 337) frequency-matched by age (+/- 5 years), gender, and race were identified through random-digit dialing. In-person interviews assessed smoking history and lifetime exposure to ETS at home, work, and public spaces. Home ETS was measured in both years and hours of exposure. Odds ratios and 95% confidence intervals were calculated using logistic regression, controlled for age, gender, race, and BMI.ResultsCases were more likely to have smoked 20 or more pack-years, compared with never-smokers (OR: 1.35, 95% CI: 0.93 – 1.95). A protective effect was found for smoking cessation, beginning with 11–20 years of cessation (OR: 0.39, 95% CI: 0.18–0.85) and ending with 51 or more years of cessation (OR: 0.11, 95% CI: 0.03–0.39) in comparison with those having quit for 1–10 years. Among never-smokers, cases were more likely to report home ETS exposure of greater than 20 years, compared with those never exposed to home ETS (OR: 2.18; 95% CI: 1.14–4.18). Home ETS associations were comparable when measured in lifetime hours of exposure, with cases more likely to report 30,000 or more hours of home ETS exposure (OR: 2.37; 95% CI: 1.20–4.69). Highest quartiles of combined home/work ETS exposure among never-smokers, especially with public ETS exposure, increased RCC risk by 2 to 4 times.ConclusionThese findings confirm known associations between smoking and RCC and establish a potential etiologic role for ETS, particularly in the home. Differences in methods of retrospective measurement of lifetime smoking and ETS exposure may contribute to discrepancies in measures of associations across studies, and should be addressed in future research.

Food groups and renal cell carcinoma: results from a case-control study.

BACKGROUND The role of diet in renal cell carcinoma risk has been inconclusive. This study uses an integrative approach to assess the role of food groups and food items in renal cell carcinoma risk. DESIGN A case-control study was conducted from 2003-2006. SUBJECTS/SETTING Incident cases (n=335) were identified from hospital records and the Florida cancer registry, and population controls (n=337) frequency matched by age (+/-5 years), sex, and race were identified through random-digit dialing. Eating habits were assessed through the use of the 70-item Block food frequency questionnaire. STATISTICAL ANALYSES Odds ratios (ORs), 95% confidence intervals (CIs), and tests for trends were calculated using logistic regression, controlled for age, sex, race, income, body mass index, and pack-years of smoking. RESULTS Decreased renal cell carcinoma risk was observed among the total sample and for men for vegetable consumption (all subjects: OR 0.56, 95% CI 0.35, 0.88; men: OR 0.49, 95% CI 0.25, 0.96) but not for fruit consumption. Tomato consumption decreased renal cell carcinoma risk for the total population and for men (all subjects: OR 0.50, 95% CI 0.31, 0.81; men: OR 0.47, 95% CI 0.24, 0.95). Increased risk of renal cell carcinoma was observed among all subjects and among women with increased consumption of red meat (all subjects: OR 4.43, 95% CI 2.02, 9.75; women: OR 3.04, 95% CI 1.60, 5.79). White bread consumption increased renal cell carcinoma risk among women only (OR 3.05, 95% CI 1.50, 6.20), as did total dairy consumption (OR 2.36, 95% CI 1.21, 4.60). CONCLUSIONS The protective role of vegetables and the increased risk of renal cell carcinoma with meat consumption are supported. The protective role of fruits is not. Novel findings include the increased risk of renal cell carcinoma with white bread and white potato consumption and the decreased risk of renal cell carcinoma with tomato consumption.

Functional Impairment as a Predictor of Spine Loading

Study Design. Spine loadings during a variety of lifting exertions were compared with individual torso kinematic abilities. Relationships were evaluated between these measures. Objective. To determine if trunk kinematic status (functional impairment) is indicative of spine loading increases in patients with low back pain (LBP) compared to asymptomatic individuals. Summary of Background Data. Recurrent LBP is a common and costly problem that may be related to increased spine loads in those individuals with LBP. Previous studies suggest that patients with LBP had greater loading than their asymptomatic counterparts when performing work. However, we know little about how to identify when a patient with LBP can resume lifting tasks without having exaggerated spine loading. Methods. Sixty-two patients with LBP and 61 who were asymptomatic were evaluated for signs of kinematic compromise (i.e., inability to generate normal trunk kinematic patterns) during a prelift test. All subjects were then asked to perform a variety of lifting exertions that varied in lift origin (region), lift asymmetry position, and weight lifted. An electromyography-assisted model was used to evaluate spine loading in each subject during the lifting exertions. Statistical models were used to assess the relationship between kinematic compromise and spine loading. Results. Patients with LBP had greater spine loading as well as greater kinematic compromise. The degree of kinematic compromise was related to the degree of spine loading increases in those individuals with LBP. A statistical model was developed that was able to describe 87% of the variability in compression, 61% in anteroposterior shear, and 65% in lateral shear. Conclusions. Those patients with greater kinematic compromise used higher levels of antagonistic muscle coactivation that not only reduced trunk motion but also resulted in increases in spine loading. Given the degree of kinematic compromise and the lifting task conditions, a method has been devised to predict the increase in spine loading above and beyond that of an asymptomatic individual when performing typical materials handling tasks.

A comparison of fatigue failure responses of old versus middle-aged lumbar motion segments in simulated flexed lifting

Study Design. Survival analysis techniques were used to compare the fatigue failure responses of elderly motion segments to a middle-aged sample. Objectives. To compare fatigue life of a middle-aged sample of lumbosacral motion segments to a previously tested elderly cohort. An additional objective was to evaluate the influence of bone mineral content on cycles to failure. Summary of Background Data. A previous investigation evaluated fatigue failure responses of 36 elderly lumbosacral motion segments (average age, 81 ± 8 years) subjected to spinal loads estimated when lifting a 9-kg load in 3 torso flexion angles (0°, 22.5°, and 45°). Results demonstrated rapid fatigue failure with increased torso flexion; however, a key limitation of this study was the old age of the specimens. Methods. Each lumbosacral spine was dissected into 3 motion segments (L1–L2, L3–L4, and L5–S1). Motion segments within each spine were randomly assigned to a spinal loading condition corresponding to lifting 9 kg in 3 torso flexion angles (0°, 22.5°, or 45°). Motion segments were statically loaded and allowed to creep for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). Results. Compared with the older sample of spines, the middle-aged sample exhibited increased fatigue life (cycles to failure) in all the torso flexion conditions. Increased fatigue life of the middle-aged specimens was associated with the increased bone mineral content (BMC) in younger motion segments (mean ± SD, 30.7 ± 11.1 g per motion segment vs. 27.8 ± 9.4 g). Increasing bone mineral content had a protective influence with each additional gram increasing survival times by approximately 12%. Conclusion. Younger motion segments survive considerably longer when exposed to similar spine loading conditions that simulate repetitive lifting in neutral and flexed torso postures, primarily associated with the increased bone mineral content possessed by younger motion segments. Cycles to failure of young specimens at 22.5° flexion were similar to that of older specimens at 0° flexion, and survivorship of young specimens at 45° flexion was similar to the older cohort at 22.5°.

The influence of lift frequency, lift duration and work experience on discomfort reporting

Discomfort surveys are commonly used to assess risk in the workplace and prioritize jobs for interventions before an injury or illness occurs. However, discomfort is a subjective measure and the relationship of discomfort to work-related factors is poorly understood. The objective of this study was to understand how reports of discomfort relate to work-related risk factors for the low back. A total of 12 novice and 12 experienced manual materials handlers performed repetitive, asymmetric lifts at different load levels and at six different lift frequencies throughout an 8-h exposure period. Discomfort was recorded hourly throughout the day. Analyses were performed to determine which experimental factors influenced reporting of discomfort and if discomfort trends matched spine loading trends. Novice lifters reported significantly higher discomfort levels than experienced subjects. They also reported increases in discomfort as moment exposure increased and as the exposure time increased. Novices lifting at 8 Nm load moment level reported increased discomfort from 0.07 to 0.63 by the end of the day, at 36 Nm they reported an increase from 0.04 to 0.40 and at 85 Nm they reported an increase from 0.37 to 3.06. Experienced subjects, on the other hand, reported low levels of discomfort regardless of moment exposure, lift frequency or exposure duration. The reported discomforts were generally unrelated to the biomechanical loading on the spine. Discomfort reporting appears to be more a reflection of experience than of work risk factor exposure. Experienced subjects may have more efficient motor patterns, which reduce spinal load and thus discomfort. Novice subjects seemed to have a lower threshold of discomfort. Caution is needed when using discomfort reporting as a means to identify jobs in need of interventions, in that biomechanical loading may not be accurately represented. Discomfort should only be used as a supplement to objective measures, such as spinal loading, to assess the risk of low back disorders.