On associations between different factors and whiplash injury

Sammanfattning: The overall aim of this thesis was to evaluate associations between different factors and whiplash injury (defined as a soft tissue injury to the neck without fracture or dislocation), focusing on risk of initial and future complaints. The objectives in Paper 1 and II was to determine whether exposure to a rear-end collision, with or without whiplash injury, is associated with future neck or shoulder pain (Paper 1) and other health complaints, besides neck pain (Paper II). The purpose of the third article was to evaluate whether occupant- and crash-related factors, such as age, gender, seating position and type of motor vehicle crash (MVC) are associated with the risk of whiplash injury, given that an MVC had occurred and at least one occupant in the car has been injured. In the fourth paper, the aim was to estimate the effect of potential prognostic factors on the presence of neck pain over a 2-year period among subjects with whiplash injury. The first and the second paper were based on the same study population. Claim reports were collected from the period November 1987 to April 1988. Drivers exposed to a rear-end collision were divided into two subgroups: those with reported whiplash injury (n=232) and those without reported whiplash injury (n=204). For comparison, 3688 subjects who were unexposed to MVCs were selected, with consideration taken to the age and gender distribution in the exposed subgroups. The prevalence of different health complaints among the study subjects was estimated according to a mailed questionnaire at follow-up in 1994, 7 years after the rear-end collision. The age- and gender-adjusted relative risk (RR) of health complaints at follow-up was calculated for subjects in each exposed subgroup as compared with unexposed subjects, using the Mantel-Haenszel technique. In the third article a study of occupants in cars covered by motor insurance at one of the largest insurance companies in Sweden, was undertaken during a one-year period. The study population comprised all occupants in cars exposed to an MVC in which at least one occupant was injured (n=7120). Adjusted estimates of the relative risk of whiplash injury, associated with the different occupant- and crashrelated factors, were calculated by means of binomial regression analysis. In the fourth paper, the association between potential prognostic factors and the presence of neck pain at follow-up was estimated in subjects with whiplash injury at one month, six months, one year and two years after the MVC (n=2280), by calculating odds ratios (OR) together with 95% confidence intervals (Cl). The outcome, i.e., neck pain, was defined as a score of 60 mm and over on a 100 mm visual analogue scale (VAS). The simultaneous effect of several potential prognostic factors was calculated by means of logistic regression. A separate analysis was carried out for each of the four different follow-ups, respectively. In Paper I, it was shown that the relative risk of neck or shoulder pain at follow-up was 1.3 (95% Cl 0.8-2.0) in the exposed subjects without whiplash injury compared with the unexposed. The corresponding relative risk in subjects with whiplash injury was 2.7 (95% Cl 2.1-3.5). For this group, increased relative risks were also seen for headache, thoracic and low back pain, as well as for fatigue, sleep disturbances and ill health (RR in the range of 1.6- 3.7) (Paper 11). No corresponding increased risks were found among the exposed subjects without reported whiplash injury. In Paper Ill it was found that, considering different MVCs, rear-end collisions were associated with the highest relative risk of whiplash injury when compared with side impacts (1.82; 95% Cl 1.68-1.96), while drivers showed the strongest association with respect to seating position when compared with passengers in the rear seat (1.78; 95% Cl 1.60-1.97). Females had a somewhat higher risk of whiplash injury compared with males (RR 1.20; 95% Cl 1.16-1.25). No interaction between the studied factors was observed on the additive scale. In Paper IV, it was demonstrated that the most pronounced prognostic factor was neck pain intensity at baseline, with an OR in the range of 15 to 39 at the different followups, respectively. Compared with subjects with a low degree of perceived helplessness, the odds ratio increased with higher degrees of helplessness and the strength of the association remained relatively constant over time. The OR was 5.6 (95% Cl 2.8-11.2) and 5.1 (95% Cl 2.5-10.3) at the one- and twoyear follow-ups, respectively, for subjects reporting a high degree of helplessness at baseline. Females had an approximately twofold increased odds of having neck pain compared with men. The studies included in this thesis have added important knowledge regarding risk factors for whiplash injury, as well as for factors of relevance for future consequences due to whiplash injury.