33 and 34 Moreover, these groups may have different expectations concerning RTW, which could lead to a higher dropout rate from rehabilitative interventions.35 In this study, they represented 50% of patients. Although, studies about the role of the mother language are scarce, 1 study36 reported that the mother language, among others, was a predictor for non-RTW. Additionally, a non-Swiss mother language is related to a low health literacy, which may cause a substantial burden to society and the injured person.37 Understanding the role of language in the development of chronic WADs may be crucial for developing effective work disability

prevention programs for patients with WADs. Predicting RTW in patients with chronic pain is difficult. Lifting tests explain 10% to 20% of the variance in RTW in patients with musculoskeletal disorders.38 Some authors reported an explained variance up to 27%,39 while others suggested that adding FCE tests find more to self-reported data would increase the explained variance from 9% to 16%.40 However, others reported a 10% explained variance, questioning the predictive value of FCE tests for RTW in patients with chronic musculoskeletal pain.41 and 42 These differences may be explained by differences in study design (eg, cross-sectional vs prospective) or sample size ranging from 5 to 20 events per prognostic association tested. Follow-up times may range from 1 to 12 months, statistical

models may use uni- or multivariate analysis that corrects for confounders.8 Moreover, buy PR-171 results between studies may Vasopressin Receptor differ based on the definition of RTW used, which can be measured by self-report or insurance data. Also social security systems between different countries may lead to different results. This study shows that the strength of the correlation between WC and FCE tests is related to the time point after the whiplash injury. Most of the patients in this study reached full WC within the 12-month follow-up period. This is in contrast to other studies1 and 2 showing that a substantial proportion of patients with WADs (40%–60%) still have varying levels of pain and self-reported disability after 1 year.

We hypothesized that WC over 12 months may not be indicative of perceived disability. In a post hoc analysis, we evaluated the correlation between WC and the available NDI scores at 3 and 12 months (50% of the study sample). The correlations were low (r<0.3; WC accounts for 9% of the explained variance of NDI), indicating that disability and WC are related but distinct constructs. While it may be methodologically correct to study FCE tests separately, in clinical work, FCE tests are used in conjunction with medical records, patient interviews, musculoskeletal evaluation, and job-specific observations.11 One may argue that predictive values would be higher if RTW can be predicted based on the full clinical package, including FCE tests. Results of this strategy are indeed positive.