Abstract
BACKGROUND: A neck-specific exercise program has shown sustained clinically important changes in pain and disability for approximately 50% of individuals with chronic whiplash-associated disorders (WAD). However, there is limited information about factors related to treatment response. OBJECTIVE: The aim of this study is to identify factors related to changes in disability, neck pain, and physical function after a neck-specific exercise program delivered in 2 different ways for individuals with persistent WAD grade II or III, and to investigate whether any factors could predict those with clinically improved versus not improved disability, pain, and physical function. METHODS: This was a planned secondary analysis of a multicenter prospective randomized controlled trial. Participants (n=140) with persistent (between 6 mo and 5 y from injury) WAD grade II or III were randomized into a 12-week, internet-based neck-specific exercise program (NSEIT) with 4 physiotherapy visits or the same exercise program supervised by a physiotherapist (NSE) twice per week for 12 weeks. Multivariate data analyses and orthogonal partial least squares (OPLS) models were used to investigate change in psychological and physiological factors (independent factors) related to change in the dependent factors: neck-related disability measured with the Neck Disability Index (NDI), neck pain intensity measured with a visual analogue scale, and physical function measured with the Patient-Specific Functional Scale (PSFS). Outcomes were measured at baseline and at 3-month and 15-month follow-up. OPLS discriminant analysis was used to investigate differences between the two groups (NSEIT and NSE) by studying the change scores of the dependent and independent factors. OPLS discriminant analysis was also used to investigate whether background variables and baseline measurements of the independent factors could predict clinically significant improvement in the dependent factors NDI, neck pain, and PSFS. RESULTS: There were no significant differences between the groups. In both NSEIT and NSE, improvements in the following independent factors were related to improvements in NDI, pain, and PSFS at 3-month and 15-month follow-up: anxiety, depression, cognitive failures, pain catastrophizing, self-efficacy, fear avoidance beliefs, cervical range of motion, headache, and symptom satisfaction (R2=0.31-0.37; Q2=0.25-0.30; cross-validated ANOVA P<.001). No significant OPLS models could be built to distinguish clinically improved versus nonimproved patients as assessed by NDI, neck pain, or PSFS. CONCLUSIONS: Improvements in both psychological and physiological factors were related to improvements in disability, neck pain, and physical function after 12 weeks of NSEIT or NSE. The results indicate that these factors are interrelated and can be improved both with NSEIT and NSE. Known risk factors for poor outcomes of neck disability in WAD, such as low self-efficacy, fear avoidance beliefs, depressive symptoms, and catastrophizing, were improved, and we need to examine other factors not included in this study that can identify those who are not improved after NSEIT or NSE.