Accepted Manuscript Can functional capacity tests predict future work capacity in patients with whiplashassociated disorders? Maurizio A. Trippolini, MSc Pieter U. Dijkstra, PhD Pierre Côté, PhD Stefan M. Scholz-Odermatt, PhD Jan H.B. Geertzen, PhD Michiel F. Reneman, PhD PII:
S0003-9993(14)00934-4
DOI:
10.1016/j.apmr.2014.07.406
Reference:
YAPMR 55923
To appear in:
ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION
Received Date: 3 March 2014 Revised Date:
30 June 2014
Accepted Date: 16 July 2014
Please cite this article as: Trippolini MA, Dijkstra PU, Côté P, Scholz-Odermatt SM, Geertzen JHB, Reneman MF, Can functional capacity tests predict future work capacity in patients with whiplashassociated disorders?, ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION (2014), doi: 10.1016/j.apmr.2014.07.406. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Title page
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Title
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Can functional capacity tests predict future work capacity in patients with whiplash-associated disorders?
5 Authors
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Maurizio A. Trippolini, MSc
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, Pieter U. Dijkstra, PhD
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PhD , Jan H. B. Geertzen, PhD , Michiel F. Reneman, PhD
, Pierre Côté, PhD 2
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, Stefan M. Scholz-Odermatt,
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Affiliations
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Department of Work Rehabilitation, Rehaklinik Bellikon, Suva Care, Bellikon, Switzerland
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Department of Rehabilitation Medicine, Center for Rehabilitation, University Medical Center Groningen, University of Groningen,
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Department of Oral and Maxillofacial Surgery, University Medical Center Groningen, University of Groningen, Groningen, The
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Division of Epidemiology, Della Lana School of Public Health, University of Toronto, Toronto, Canada
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University of Ontario, Institute of Technology, Faculty of Health Sciences, Oshawa, Canada
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Central Office for Statistics in Accident Insurance (SSUV), Lucerne, Switzerland
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Author disclosures:
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Part of the study was funded by the Swiss Accident Insurance Fund, SUVA (Schweizerische
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Unfallversicherungsanstalt)
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Two authors (MAT, SSO) are employed by the SUVA. However, no funding bodies had any role in study
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design, data collection and analysis, decision to publish, or preparation of the manuscript.
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This work has not been presented elsewhere.
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Groningen, The Netherlands
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Netherlands
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For correspondence and reprints, contact:
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M. A. Trippolini, Department of Work Rehabilitation, Rehaklinik Bellikon, 5454 Bellikon, Switzerland. Tel.
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+41 56 485 56 10; E-mail:
[email protected]
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Acknowledgements
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The authors thank the physiotherapists and the physicians of the Department of Work Rehabilitation, Rehaklinik
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Bellikon who participated in this study.
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Tables: 2 count. Figures: 2 count. Text box: 1 count
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Short running head: predictive ability of functional capacity tests for future work capacity
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Abstract
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Objective: To determine whether Functional Capacity Evaluation (FCE) tests predict future work capacity of
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patients with whiplash-associated disorders (WAD) grades I and II who did not regain full work capacity 6-12
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weeks after injury.
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Design: Prospective cohort study.
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Setting: Rehabilitation center.
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Participants: Workers listed as sick with WAD 6 to 12 weeks after injury.
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Interventions: Patients performed 8 work-related FCE tests.
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Main Outcome Measures: Work capacity (WC; 0-100%) measured at baseline and 1, 3, 6, and 12 months after
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testing. Correlation coefficients between FCE tests and WC were calculated. A linear mixed model analysis was
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used to assess the association between FCE and future WC.
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Results: In total, 267 patients with grade I or II WAD participated in the study. Mean WC increased over time
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from 20.8 (SD 27.6) at baseline to 32.3 (SD 38.4), 51.3 (SD 42.8), 65.6 (SD 42.2), and 83.2 (SD 35.0) at the 1, 3,
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6, and 12-month follow-up respectively. Correlation coefficients between FCE tests and WC ranged from r=0.06
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(lifting low at 12-month follow-up) to r=0.39 (walking speed at 3 months). Strength of the correlations decreased
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over time. FCE tests did not predict WC at follow-up. The predictors of WC were ln (time) (β = 23.74), mother
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language (β=5.49), work capacity at baseline (β=1.01), and self-reported disability (β=-0.20). Two interaction
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terms ln (time) x workcapacity (β=-0.19), and ln (time) x self-reported disability (β=-0.21) were significant
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predictors of WC.
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Conclusion: FCE tests performed within 6-12 weeks after WAD injury grades I and II are associated with WC
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at baseline, but do not predict future WC, whereas time course, mother language, WC at baseline, and self-
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reported disability do predict future WC. Additionally, the interaction between time course WC at baseline and
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self-reported disability predicted future WC.
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Keywords: Disability Evaluation, Whiplash injury, Neck pain, Prognosis, Prediction
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List of abbreviations
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FCE
functional capacity evaluation
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WAD
whiplash-associated disorders
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WC
work capacity is the proportion of workability as a percent of the current work as determined
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RTW
return-to-work
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LBP
low back pain
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by the physician
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The prognosis of whiplash-associated disorders (WAD) is generally favorable, with recovery rates of 40-60%
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within the first year. However, many individuals with WAD report symptoms and disability one year after the
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initial injury1, 2 . Due to long term sickness absence and work disability, delayed recovery from WAD causes a
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substantial burden to individuals and society3. Several studies have investigated prognostic factors for the
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clinical course of WAD4, 5. Established prognostic actors include post-injury pain intensity and self-reported
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disability1. Psychosocial factors such as fear of movement, self-efficacy beliefs, poor recovery expectation, pain
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catastrophizing, passive coping and depression predict poor recovery2, 4, 6, 7. Studying the prognosis of whiplash
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is complicated and the validity of previous studies has been limited by small sample size, inclusion of patients
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>6 months after injury onset, short follow-up periods (0.05).
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significantly related to the outcome variable and the time course were explored. Residuals of the linear mixed
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model analyses were plotted in a graph and visually assessed for normality. Data were analyzed in SPSS version
Finally, two-way interactions between the predictors that were
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Results
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Descriptive statistics of the study population
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A total of N=267 patients were included. Patient characteristics are displayed in Table 1.
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Table 1.
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Mean WC was 20.8 (SD 27.6) at baseline and 32.3 (SD 38.4), 51.3 (SD 42.8), 65.6 (SD 42.2), 83.2 (SD 35.0) at
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the 1, 3, 6, and 12-month follow-up respectively (Figure 1). In a post-hoc analysis, we compared the patients’
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WC and corrected for the region of the insurance to which they were referred; no regional differences were
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observed.
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Figure 1.
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Bivariate analysis
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Correlation coefficients between FCE tests and WC decreased over time for most variables (Figure 2). The
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correlation coefficients ranged from r=0.06 (lifting low at 12-month follow-up) to r=0.39 (walking speed at 3
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months). At follow-up, walking speed and SED showed the highest correlations with WC.
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Figure 2.
2 Mixed model analysis
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The results of the mixed model analysis for all follow up times at the 1, 3, 6 and 12-month follow-up are
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presented in Table 2. In step 1 the following 3 FCE tests predicted WC: repetitive reaching, walking speed and
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the SED score (data from step 1 are available on request). The regression coefficients of the three FCE tests in
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the model decreased from step 2 to step 3 by -0.05 for repetitive reaching, -5.45 for walking speed, and -1.76 for
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SED score. From all 18 predictor variables, nine (age, gender, BMI, marital status, duration since injury, attorney
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involved, work status, education, and physical work demands) did not change regression coefficients of the three
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FCE tests variables by >10%, and were therefore not considered for the next step. In step 4 the remaining nine
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predictor variables (work capacity at baseline, mother language, number of prior injuries, pain level, perceived
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recovery, perceived functional ability, disability, anxiety and depression), together with the three FCE tests and
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Ln (weeks+1) were entered in the model (table 2, step 3). None of the FCE tests remained significant predictors
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of future WC. Therefore, FCE tests were excluded from the final model. The final prognostic model included;
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Ln (weeks+1) (β=23.74), mother language (β=5.49), work capacity at baseline (β=1.01) and self-reported
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disability (β= -0.20). All the two-ways interactions between these four predictors were explored. Two
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interactions terms were significant: Time course mediates work capacity and self-reported disability, as those
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two interaction terms remained significant. Overall, time course and mother language were the predictors with
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the highest regression coefficients. To facilitate interpretation of the results of the linear mixed model analysis,
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two clinical examples were calculated (Appendix 2).
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Appendix 2.
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Discussion
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We conducted a prospective cohort study to determine the prognostic ability of FCE tests to predict WC and
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developed a predictive model in a cohort of patients with WAD. Correlation coefficients between FCE tests and
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WC were
