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Factors Influencing Results of Functional Capacity Evaluations in Workers' Compensation Claimants With Low Back Pain

Douglas P Gross, Michele C Battié

Abstract

Background and Purpose. Physical and psychosocial factors are hypothesized to influence performance-based assessment. The purpose of this study was to evaluate the association between performance on the Isernhagen Work System Functional Capacity Evaluation (IWS-FCE) and various clinical and psychosocial factors. Subjects. The sample consisted of 170 workers' compensation claimants who were undergoing functional capacity evaluations (FCEs) for low back injuries. Methods. In this cross-sectional study, claimants completed a battery of work-related measures, including the IWS-FCE, the Pain Disability Index (PDI), a workplace organizational policies and practices scale, and a recovery expectations questionnaire. Functional capacity evaluation performance indicators were the number of tasks in which subjects did not meet work demands and weight lifted on the floor-to-waist lift. Analysis included multivariable regression. Results. Only the PDI, pain intensity, age, and sex independently contributed to floor-to-waist lift performance. The PDI, pain intensity, and duration of injury contributed to the number of failed tasks. Discussion and Conclusion. The results indicate that performance on FCEs is influenced by physical factors, perceptions of disability, and pain intensity. However, perceptions of workplace organizational policies and procedures were not associated with FCE results for workers' compensation claimants with chronic back pain disability. Functional capacity evaluations should be considered behavioral tests influenced by multiple factors, including physical ability, beliefs, and perceptions.

Rehabilitation professionals frequently use performance-based functional measures to determine degree of functional impairment, evaluate success with intervention, and predict future ability.1 When compared with self-report measures, performance-based tests have traditionally been considered more accurate and free from bias because muscle force, joint mobility, cardiovascular endurance, and other physical traits are considered the main performance-limiting factors as opposed to patient beliefs or perceptions.13 However, greater attention is being paid to psychological and broader contextual factors when interpreting the results of functional tests, especially those performed within the context of a workers' compensation or other insurance system.4,5

Functional capacity evaluations (FCEs) are examples of clinical measures using performance-based testing.6 They are standardized batteries of functional measures commonly used to determine injured workers' abilities to perform work-related activities. Recommendations are made based on FCE results regarding employability, including whether a person can safely return to preinjury or modified employment. Although many FCE batteries include both performance-based and self-report measures, observation of a person's physical abilities by a trained FCE administrator is highly valued.7 In some FCEs, including the Isernhagen Work Systems'* assessment protocol (IWS-FCE), only rater observations of participant physiological and biomechanical responses to testing are used to determine effort levels and judge maximal performance.2

Individual physical traits are commonly believed to influence performance-based testing, and men, due to their larger muscle mass, consistently outperform women on tests of muscle force.810 Geisser et al,4 however, recently published a narrative review related to FCE practice in which they posited that performance-based FCE testing also is influenced by various nonphysical factors, including pain perceptions, self-efficacy beliefs, and work-related perceptions such as job satisfaction and workplace support, among others. If psychosocial factors influence performance during FCEs, the validity of data obtained with FCEs as tests of strictly physical function would be questioned. Although Geisser et al acknowledged that little research has been done to elucidate the presence, magnitude, or causal mechanisms of the specific relationships discussed, the available evidence in the area of FCE appears to support some of their conclusions.

Several authors9,11,12 have reported that performance on FCEs by subjects with chronic low back pain is moderately associated with pain intensity ratings, with subjects reporting higher pain levels consistently performing at lower levels. Moderate relationships also have consistently been reported between perceived disability measures and FCE lifting performance in subjects with chronic low back pain, with subjects reporting higher levels of disability consistently lifting at lower levels.11,13,14 Additionally, Lackner and colleagues9,15 have reported that functional self-efficacy (or the confidence a person has that a particular behavior can be performed independently) influences FCE performance. In a sample of 100 patients with work disabilities, Lackner and Carosella9 found that the patients' ratings of their confidence in performing lifting tasks independently predicted actual lifting ability. Results related to other psychological factors hypothesized to be associated with performance-based functional testing, such as kinesiophobia, have been inconsistent and warrant further research.16,17

To our knowledge, the relationship between performance-based functional testing and work-related psychological factors, such as perceptions of support in the workplace, has not been investigated. Additionally, we were unable to locate research on the relationship between performance-based testing and work-related recovery expectations. However, both negative occupational perceptions and recovery expectations are important prognostic factors that have been associated with delayed recovery following work-related injury.1820 We theorized that low levels of perceived support at work and poor expectations regarding the consequences of return to work might diminish a person's motivation to perform and thus result in lower functional performance levels.

In the present study, we examined the relationship between various clinical and psychosocial factors and a performance-based functional assessment, the Isernhagen Work System Functional Capacity Evaluation (IWS-FCE). Because we were investigating associations among abstract constructs, we judged the magnitude of a relationship to be low if correlation coefficients varied between 0 and .29, moderate if coefficients were between .3 and .59, and strong if coefficients were above .6, as recommended by Innes and Straker21 for FCE construct validity investigations. We hypothesized that higher levels of perceived disability, increasing ratings of pain severity, more negative work-related recovery expectations, and lower perceptions of workplace support would each be moderately and independently associated with decreasing functional performance levels on FCEs. We also hypothesized that age and sex, due to their association with muscle force, would be independently associated with FCE performance, because greater muscle force is anticipated to result in higher physical performance levels.

Method

Design

A cross-sectional study design was used. Information on FCE and the self-report measures were obtained during administration of a work assessment battery in a clinical setting. Information obtained from the work assessment battery was being used for purposes of claims decision making, including determination of fitness to return to work. Data on primary measures of interest and descriptive characteristics, including subject age, sex, diagnosis, duration of injury, Human Resources Development Canada's National Occupational Classification physical demands code (sedentary, light, medium, or heavy manual work),22 and employment status (whether or not they had a job to return to) were extracted from a clinical database. Data collection was performed as part of a larger project approved by the University of Alberta's Health Research Ethics Board.

Subjects

Subjects were all claimants who met the study inclusion criteria and were seen for FCE testing between April 1, 2001, and March 31, 2002, at the major workers' compensation rehabilitation facility in Alberta, Canada. Specific inclusion criteria were: compensated work-related injuries with ICD-9 codes indicative of injury to the lower back, medical clearance to participate in FCE, and not discharged for further medical investigation or treatment. Claimants referred for FCE testing within the Alberta workers' compensation environment are usually those who have met or surpassed expected injury healing times and have plateaued with medical and rehabilitative interventions, yet report ongoing difficulties related to their compensable condition. Such claimants are evaluated with FCE for purposes of determining fitness to return to work and employability.

Performance-Based Functional Measures

The IWS-FCE protocol is used throughout Alberta's Workers' Compensation Board's health care provider network. Isernhagen Work Systems representatives trained all clinicians performing FCEs at the center from which data were obtained. All clinicians were either licensed physical therapists or occupational therapists. The IWS-FCE protocol includes a battery of physical performance tests representing the physical demands of work outlined in the Dictionary of Occupational Titles23,24 (Figure) and has been described in detail elsewhere.23,24 For our analysis, 2 FCE performance measures were used: the floor-to-waist lift and the number of failed tasks.

Figure.

Test items within the Isernhagen Work Systems Functional Capacity Evaluation.

Floor-to-waist lift.

The maximum amount of weight lifted (in kilograms) during the floor-to-waist lift in the IWS-FCE protocol was recorded for each subject. The IWS-FCE protocol recommends testing lifting ability with sets of 5 repetitions, and the criteria for determining safe, maximal effort have been discussed elsewhere.25 We selected this task because it has been found to yield data that have good interrater and test-retest reliability25,26 and adequate construct validity as a measure of work-related function11 and that are weakly associated with future return to work.27,28 Higher lift scores are indicative of better performance.

Number of failed tasks.

Although Isernhagen7 suggested that a return-to-work recommendation should be made following FCE when a client demonstrates performance that meets or exceeds all job requirements, our previous investigations have demonstrated that very few clients (∼5%) actually pass all items in the IWS-FCE protocol.28 For this reason, the number of tasks rated as failed by the administering clinician (out of 25) was recorded for each subject. These ratings are central to individual determinations of readiness to return to work. Higher scores are indicative of worse performance. A clinician rating of the number of failed tasks as an indicator of FCE performance has been reported to have adequate construct validity and is weakly associated with future recovery.11,28

Self-Report Measures

Pain Disability Index.

The Pain Disability Index (PDI) is a measure of perceived disability due to pain. It has been tested in a variety of patient populations, including those with chronic back pain.2931 The PDI asks patients to rate their level of disability on a 0-to-10 scale on 7 areas of activity. A person's scores on these 7 items are summed for a total score between 0 and 70, with higher scores indicative of higher levels of perceived disability. Percentage PDI, calculated as an individual's total score divided by the total possible score for only the items completed, has been recommended to overcome problems with missing data.32 Gronblad et al33 found both overall PDI score and percentage score correlated strongly and nearly equivalently with scores on the Oswestry Disability Questionnaire, and our research group has reported similar findings when comparing the overall PDI score and percentage score with indicators of FCE performance.11 Percentage PDI was used in the present analysis.

Previous investigators32,33 have reported good test-retest reliability, high internal consistency, and good concurrent validity for the PDI when tested against the Oswestry Disability Questionnaire in a group of subjects with low back pain. The PDI has been shown to accurately discriminate between patients who had just undergone back surgery and patients with low back pain maintaining full-time work.34 Scores on the PDI also have been reported to correlate moderately with both weight lifted during FCE and the number of failed FCE tasks.11

Pain visual analog scale.

The pain visual analog scale (VAS) is a measure of perceived pain severity that is reported to yield reliable and valid data.1 The scale used in the present study is anchored at both ends, with 0 (“no pain”) at one end and 10 (“unbearable pain”) at the other end. Higher pain intensity ratings have been reported as moderately associated with lower FCE lifting ability.9,11,12 In the work assessment battery, both the VAS and the PDI are typically administered either prior to FCE testing or during the protocol while the client performs the 30-minute stand or sit tests, prior to a verbal debriefing in which the clinician discusses with the client his or her overall performance on the FCE.

Work-related recovery expectations questionnaire.

As previously mentioned, injured workers' beliefs regarding their likelihood of returning to work have been found to be associated with future recovery in several studies.19,20,35 Recovery expectations appear to influence both functional and symptomatic recovery in addition to return to work and, therefore, may influence demonstrated performance on performance-based functional testing.20 Various measures of recovery expectations have been used,19,20 ranging from simple questions to more detailed questionnaires. At the time this study was undertaken, however, no well-investigated or widely used measure of recovery expectations existed. We, therefore, created a measure consisting of 3 items (Appendix) on which subjects rated their level of agreement with statements regarding their beliefs about current and future work abilities on a 5-point Likert scale (1=“strongly disagree,” 5=“strongly agree”). The first item's response direction is reversed compared with the other 2 items to allow us to evaluate whether subjects read and comprehended each item. Prior to implementing this measure widely at the rehabilitation facility, we undertook pilot testing of the tool using 2 focus groups to ensure that the items would be clear and acceptable to injured workers. We also evaluated this measure's internal consistency using the Cronbach alpha and judged it to be adequate (α=.75).

Organizational policies and practices.

Amick et al18 developed a workplace organizational policies and practices (OPP) scale designed to measure individuals' perceptions of support at the workplace. The measure consists of 22 statements, on which people are asked to rate their level of agreement using a 5-point Likert scale ranging from 1 (“strongly disagree”) to 5 (“strongly agree”). Four factors have been identified in the OPP scale: unique constructs of people-oriented culture, safety climate, ergonomic practices, and disability management policies and practices. Intraclass correlation coefficients for test-retest reliability have been reported to range between .78 and .88, supporting the ability of workers to consistently respond over time to the items in the OPP scale.18 Additionally, the measure has some predictive ability in patients who are off work due to carpal tunnel syndrome.18

We confirmed the construct validity of data for the OPP scale using factor analysis with Promax rotation and a factor-loading criterion of 0.4 to replicate findings of the scale's developers.18 We found a factor structure remarkably similar to that reported by Amick et al18; therefore, we used the same 4 OPP scale factors and item-inclusion strategy recommended by the scale's developers. Subjects completed both the OPP scale and the work-related recovery expectations questionnaire when they first arrived at the clinic to undergo FCE testing.

Data Analysis

Univariate Pearson correlation coefficients were calculated between all variables in the work assessment battery. To examine the associations between the clinical and psychosocial factors and FCE performance while simultaneously controlling for possible confounding factors, multivariable linear regression models were created for floor-to-waist lifting and the number of failed tasks.36 All self-report variables in the assessment battery along with subject age, sex, employment status, and duration of injury were entered as independent variables. An alpha level of .05 was chosen to judge significance and entry into final models. All calculations were performed using the computer application SPSS 11.0.

Results

Of the 251 subjects who met the inclusion criteria, 170 (68%) had information on all measures except the VAS, and their data were included in subsequent analyses. Subjects with missing data were older (44 versus 41 years), had a longer time between injury and FCE (1,289 versus 450 days), and lifted less on the FCE floor-to-waist lift (10 versus 15 kg). Twenty-four (14%) of these 170 subjects had missing VAS scores and were more likely to speak English as a second language. All analyses incorporating the pain VAS measure were performed on the smaller subset of 146 subjects with available VAS data. Language, although an important potential determinant of FCE performance, was not investigated due to the small number of subjects (n=9) in our sample who did not speak English as a primary language.

The majority of subjects were men with a nonspecific diagnosis, primarily sprain or strain, who were evaluated more than 6 months following their injury (Tab. 1). Mean, median, and standard deviation scores for the FCE, PDI, and VAS measures indicated that the subjects had moderate levels of disability and pain.

Table 1.

Subject Characteristics (N=170)

In univariate analysis, moderate correlations were observed between the number of failed FCE tasks and scores on the PDI, VAS, and work-related recovery expectations questionnaire (Tab. 2). Moderate correlations also were observed between weight on the floor-to-waist lift and the PDI and VAS scores. Nonsignificant, low correlations (r=.03–.08) were observed between the FCE performance indicators and subject ratings on the 4 factors of the OPP scale.

Table 2.

Correlation Matrixa

In both multivariable linear regression analyses, collinearity was observed between the PDI and VAS variables (tolerance=0.4). Analyses, therefore, were performed with these variables entered separately. Final multivariable models are shown in Table 3. Standardized regression coefficients for the work-related recovery expectations measure became very low (β=0.07) after controlling for the PDI. When the pain VAS scores were entered as opposed to the PDI scores, the VAS scores remained significant in all final models. The adjusted R2 for the PDI (R2∼.20) and pain VAS (R2∼.10) were similar in both regressions.

Table 3.

Final Multivariable Linear Regression Models (n=170)

The PDI, VAS, age, and sex were determined to have significant, independent influences on floor-to-waist lifting, with the PDI explaining the largest amount of variation. Younger, male subjects who reported lower levels of perceived disability and pain intensity lifted at higher levels. The PDI, VAS, and duration of injury had significant, independent influences on the number of failed tasks, and again the PDI explained the largest amount of variation in the outcome. Subjects with shorter durations of injury who reported lower levels of perceived disability and pain intensity had a lower number of failed FCE tasks.

Discussion and Conclusion

In our sample of workers with compensable back injuries, self-reported ratings of perceived disability on the PDI and pain intensity using a VAS were moderately associated with both performance-based functional indicators, weight lifted on the floor-to-waist lift tasks and the number of failed FCE tasks. These findings were anticipated given that the majority of claimants undergoing FCE for low back disorders have nonspecific low back pain, a pain-mediated disability condition.28 Our results lend support to theories of functional performance in pain-mediated conditions that consider self-perceptions of disability and pain to be important influences on functional ability.5,9,37 Clinically, these factors should be measured and acknowledged in performance-based testing.

Work-related expectations of recovery also were associated with the number of failed FCE tasks. However, important confounding of the work-related recovery expectations variable was observed when the PDI scores were entered into the model. No significant influence of the expectations variable remained when simultaneously controlling for perceptions of disability, as measured with the PDI. This finding indicates that the significant univariate association between subject expectations regarding work-related recovery and FCE is mediated and explained primarily by the subjects' perceptions of what they can and cannot do as reflected through the PDI scores.

Although subject perceptions of workplace support have been theorized to influence functional testing, nonsignificant, low correlations were observed between a measure of workplace support and both our self-report and performance-based functional measures. Thus, the study results do not support the hypothesis that positive or negative perceptions of the work environment, as measured through the OPP scale, and associated motivations influence FCE performance.

The finding that younger age and male sex were associated with the floor-to-waist lift, but not the number of failed FCE tasks, is not surprising considering that the latter measure also takes into consideration the subjects' physical job demands, which are not necessarily related to individual physical capabilities. Our findings related to age and sex lend support to the view that FCE testing reflects physical capacity to some degree, even when performed within a workers' compensation context. However, we were unable to explain large amounts of the variation in FCE performance, indicating that some important determinants of performance were not measured in this study.

We previously reported that performance on one item of the IWS-FCE, floor-to-waist lifting, is as predictive of timely recovery as the number of failed tasks in the entire IWS-FCE protocol.28 In the current study, both FCE indicators (number of failed tasks and floor-to-waist lifting) were influenced to a similar magnitude by subject perceptions of disability (adjusted R2∼.20) and pain intensity ratings (R2∼.10). Potentially, these and other unmeasured factors influence subject performance on both the broader protocol and the individual lift test. This may explain the comparable predictive ability of these variables and make testing of a larger number of items redundant, because much of the meaningful information in a larger protocol can be obtained through an abbreviated version of testing. Because the entire IWS-FCE protocol appears to have limited validity for predicting sustained return to work in subjects with low back pain,38 an abbreviated test with comparable predictive power for timely return to work could make testing more cost-efficient and increase clinical utility.

The study findings are limited to workers' compensation claimants with diagnoses related to the lower back who are undergoing testing with the IWS-FCE protocol for purposes of claims decision making. Claimants undergoing FCE testing within the Alberta workers' compensation system represent a group of individuals for whom FCE is most commonly requested: those who have met or surpassed expected musculoskeletal injury healing times and are no longer progressing with intervention, yet report ongoing difficulties related to their compensable condition. The magnitude of the associations observed may not apply to all claimants on total temporary disability or those with other musculoskeletal injuries. Additionally, the work-related recovery expectations questionnaire used in this study is newly developed, and its psychometric properties beyond internal consistency have not been fully studied.

Poorer FCE performance was moderately associated with higher ratings of perceived disability and pain intensity. The FCE floor-to-waist lift performance also was independently associated with subject age and sex. Performance on the FCE appears to be influenced by both physical factors and self-perceptions of disability and pain. However, perceptions of the workplace, in terms of organizational policies, practices, and support, did not influence FCE performance in claimants with chronic low back injuries who were undergoing testing to determine fitness for work. Functional capacity evaluations should be considered behavioral tests influenced by multiple factors, including physical ability, beliefs, and perceptions.

Appendix

Appendix.

Work-Related Recovery Expectations Questionnaire

Footnotes

  • Both authors provided concept/idea/research design, writing, data analysis, and fund procurement. Dr Gross provided data collection and project management. This research was financially supported by a grant from the Alberta Heritage Foundation for Medical Research. The Workers' Compensation Board of Alberta/Millard Health facilitated data acquisition.

  • * Isernhagen Work Systems, 11 E Superior St, Suite 370, Duluth, MN 55802.

  • SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.

  • Received February 20, 2004.
  • Accepted September 8, 2004.

References

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