Can functional capacity tests predict future work capacity in patients with whiplash-associated disorders?

Abstract

To determine whether functional capacity evaluation (FCE) tests predict future work capacity (WC) of patients with whiplash-associated disorders (WADs) grades I and II who did not regain full WC 6 to 12 weeks after injury. Prospective cohort study. Rehabilitation center. Workers (N=267) listed on workers' compensation with grade I or II WADs 6 to 12 weeks after injury. Patients performed 8 work-related FCE tests. WC (0-100%) measured at baseline and 1, 3, 6, and 12 months after testing. Correlation coefficients between FCE tests and WC were calculated. A linear mixed-model analysis was used to assess the association between FCE and future WC. Mean ± SD WC increased over time from 20.8%±27.6% at baseline to 32.3%±38.4%, 51.3%±42.8%, 65.6%±42.2%, and 83.2%±35.0% at the 1-, 3-, 6-, and 12-month follow-ups, respectively. Correlation coefficients between FCE tests and WC ranged from r=.06 (lifting low at 12-mo follow-up) to r=.39 (walking speed at 3mo). Strength of the correlations decreased over time. FCE tests did not predict WC at follow-up. The predictors of WC were ln (time) (β=23.74), mother language (β=5.49), WC at baseline (β=1.01), and self-reported disability (β=-.20). Two interaction terms, ln (time) × WC (β=-.19) and ln (time) × self-reported disability (β=-.21), were significant predictors of WC. FCE tests performed within 6 to 12 weeks after WADs injury grades I and II are associated with WC at baseline but do not predict future WC, whereas time course, mother language, WC at baseline, and self-reported disability do predict future WC. Additionally, the interaction between time course WC at baseline and self-reported disability predicted future WC.