Fidelity of a stratified vocational advice intervention for improving return to work for workers on sick leave due to musculoskeletal disorders

PURPOSE: To develop a fidelity score for the Stratified Vocational Advice Intervention (SVAI), and to evaluate associations between level of fidelity to the SVAI and number of sick leave days and work ability at six months follow-up in workers on sick leave due to musculoskeletal disorders (MSDs). METHODS: The SVAI was provided by physiotherapists (PTs) who documented delivery in individual participant logs. A fidelity score was developed based on the number of follow-up sessions held, core questions documented, and a written action plan. Data were extracted from the logs and fidelity to the SVAI was categorised as “fully delivered", “partially delivered, or “not delivered” based on predetermined criteria. The number of sick leave days was calculated from registry data, and work ability was assessed using a question from the Work Ability Index on current work ability compared with the lifetime best (0–10). RESULTS: 148 SVAI logs were available for fidelity evaluation (87%). The SVAI was fully delivered to 87 (56%) participants and partially delivered to 61 (39%) participants. There was no statistically significant association between level of fidelity and sick leave days (B = 5.8, 95% confidence interval (CI) –6.2, 17.7, p = 0.34) or lower work ability (B = –0.2, 95% CI –1.4, 1.1, p = 0.77). CONCLUSION: A three-category fidelity score was developed and the SVAI was generally delivered according to protocol. There were no statistically significant associations between level of fidelity and number of sick leave days or work ability in participants at six months follow-up.