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

Abstract 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 (R 2 = 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 (R 2 = 0.26, Q 2 = 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).