Neck-related function and its connection with disability in chronic whiplash-associated disorders: secondary analysis of a randomized controlled study.

BACKGROUND: More than 40% of individuals with whiplash injury experience persistent neck pain and disability years later, called whiplash-associated disorders (WAD). A randomized controlled trial evaluated three exercise interventions in WAD and found that neck-specific exercise (NSE) and NSE with a behavioral approach (NSEB) significantly improve disability compared to prescribed physical activity (PPA). However, the relationship between neck-related function and disability is inconclusive and needs to be further investigated. AIM: The present study compares the effect of NSE, NSEB, and PPA on neck muscle endurance (NME), active cervical range of motion (AROM), grip strength, and pain intensity immediately before and after the physical tests, and neck disability in individuals who are below or above the cut-off for normative reference values regarding NME, AROM, and grip strength. DESIGN: Follow-up to a multicenter randomized clinical trial. SETTING: Primary healthcare centers and hospital outpatient services. POPULATION: The selected population of this study included 216 patients with persistent WAD grades II and III. METHODS: This is a secondary analysis including 12 months' follow-up. NME, AROM, grip strength, pain, and self-reported disability were recorded at baseline, 3, 6, and 12 months. Linear mixed models were used, and sub-group analyses evaluated by non-parametric tests. RESULTS: NSE and NSEB resulted in greater improvements compared to PPA (P<0.01) in ventral (only males) and dorsal NME, AROM, and pain intensity during testing. We found no significant between-group differences in grip strength and no significant differences between the NSE and NSEB groups. Improvement in disability was seen at the 12-month follow-up of NSE and/or NSEB for individuals both below and above the cut-off reference values for NME and AROM. Individuals in the PPA group below the reference values for NME and AROM reported increasing disability at 12 months compared to baseline. CONCLUSIONS: The results suggest that neck-specific exercises (i.e., NSE, NSEB) improve clinical function and decrease disability in chronic WAD compared to PPA, but PPA can increase disability for patients with low neck-related function. CLINICAL REHABILITATION IMPACT: Higher neck-related function seems to be important for reduced disability in persistent WAD grades II and III. Neck-specific exercises could lead to higher neck-related function.