Factors associated with 1-year health-related quality of life after neck-specific exercise in chronic whiplash-associated disorders: an exploratory secondary analysis of a randomized controlled trial

Background: Factors associated with changes in health-related quality of life (HRQoL) outcomes in neck disorders have not been investigated after internet-based support for exercise. The purpose of the study was to investigate baseline and short-term outcome factors associated with changes in HRQoL (EQ-5D-3L and EQ-VAS) at 3 and 15 months, respectively, after a neck-specific exercise programme (NSE) for individuals with chronic whiplash-associated disorders grades 2 and 3. Methods: This was a secondary analysis of a prospective randomized controlled multi-centre trial with concealed allocation. Participants (n = 140) were randomized to NSE at a physiotherapy clinic or internet-based NSE with four physiotherapy visits (NSEIT). Assessor-blinded investigators obtained measurements at baseline and at 3- and 15-month follow-up. Orthogonal partial least square (OPLS) and OPLS discriminant statistical analyses (OPLS-DA) were used. Results: There were no significant differences between the exercise programmes. Improvement in psychosocial measures, pain, disability and several objective measures were associated with improvements in HRQoL in OPLS models (R2 = 0.20 to 0.27, Q2 = 0.06 to 0.12, p < 0.05 to < 0.001). Higher baseline score on adverse psychosocial measures and disability, together with lower dizziness, self-efficacy, and neck-muscle endurance in extension, were associated with clinically relevant improvement in EQ-5D-3L at 15-month follow-up (R2 = 0.26, Q2 = 0.13, p < 0.01). The other models were non-significant. Conclusions: Several factors, including adverse psychosocial measures, may be clinically relevant for HRQoL after neck-specific exercise interventions. Given the models’ weak predictive ability, the findings should be regarded as exploratory and hypothesis-generating. Trial registration: The study was registered before data collection started, ClinicalTrials.gov Protocol ID: NCT03022812, initial release 12/20/2016. The study was approved by the regional ethical review board in Linköping, Sweden (Dnr 2016/135–31; 2016/526–32; 2017/45–32).