Six-month cost-effectiveness of adding motivational interviewing or a stratified vocational advice intervention to usual case management for workers with musculoskeletal disorders: the MI-NAV economic evaluation.

Objectives: This study evaluates the six-month cost-effectiveness and cost-benefits of motivational interviewing (MI) or a stratified vocational advice intervention (SVAI) added to usual case management (UC) for workers on sick leave due to musculoskeletal disorders.

Methods: This study was conducted alongside a three-arm RCT including 514 employed workers on sick leave for at least 50% for ≥ 7 weeks. All participants received UC. The UC + MI group received two MI sessions, and the UC + SVAI group received 1-4 SVAI sessions. Sickness absence days, quality-adjusted life-years (QALYs), and societal costs were measured between baseline and six months.

Results: Adding MI to UC, resulted in incremental cost-reduction of -2580EUR (95%CI -5687;612), and a reduction in QALYs of -0.001 (95%CI -0.02;0.01). Secondly, adding MI to UC resulted in an incremental cost-reduction of -538EUR (95%CI -1358;352), and reduction of 5.08 (95%CI -3.3;13.5) sickness-absence days. Financial return estimates were positive, but not statistically significant. Adding SVAI to UC, resulted in an incremental cost-reduction of -2899 EUR (95% CI -5840;18), and a reduction in QALYs of 0.002 (95% CI -0.02;0.01). Secondly, adding SVAI to UC resulted in an statistically significant incremental cost-reduction of -695 EUR (95% CI -1459;-3), and a reduction of 7.9 (95% CI -0.04;15.9) sickness absence days. Financial return estimates were positive and statistically significant. The probabilities of cost-effectiveness for QALYs were high for adding MI or SVAI (ceiling ratio 0.90).

Conclusions: In comparison to UC only, adding MI to UC tends to be cost-effective. Adding SVAI to UC is cost-effective for workers on sick leave due to musculoskeletal disorders.

Trial Registration: ClinicalTrials.gov (identifier: NCT03871712).