Exploring sex as a moderator of other prognostic variables in whiplash associated disorder: An observational study

Background: Prognostic variables for assessing people with whiplash associated disorder (WAD) following a motor vehicle collision (MVC) have been evaluated in numerous studies. However, there is minimal evidence assessing how these variables may differ between males and females.

Question/purpose: 1) To assess if the sex of a person interacts with known prognostic variables within the development of chronic WAD. 2) To determine if commonly used outcome measures used in the assessment of chronic WAD differ between sexes.

Methods: The study was a secondary analysis of an observational study with an inception cohort immediately following an MVC in an emergency department in Chicago, IL, USA. Ninety-seven adults aged 18 to 60 (mean 34.7 years old; 74% female) participated in the study. The primary outcome was long-term disability as determined by Neck Disability Index (NDI) scores at 52-weeks post-MVC. Data was collected at baseline (less than 1-week), 2, 12, 52-weeks post MVC. Hierarchal linear regression was used to determine significance (ΔF-score, p < 0.05) and R2 for each of the variables. The primary variables of interest were sex of the participant, age, baseline scores on the numeric pain rating scale (NPRS) and NDI and created interaction terms for sex x z-baseline NPRS and sex x z-NDI.

Results: From analysis 1, both NDI (R2 = 8.7%, p < 0.01) and NPRS (R2 = 5.7%, p = 0.02) collected at baseline predicted significant variance in NDI score at 52-weeks. The interaction term of sex x z-NPRS was also significant (R2 = 3.8%, p = 0.04). In analysis 2 the regression models when disaggregated by sex showed that baseline NDI was the significant predictor of 52-week outcome in males (R2 = 22.4%, p = 0.02) while it was the NPRS as the significant predictor in females (R2 = 10.5%, p < 0.01).