Difference in severity and distribution of bodily injuries following collision between drivers of K-cars and standard vehicles.

Background: Although K-cars, small four-wheeled vehicles with an engine capacity of <660 cc, have been used almost exclusively in Japan, they have recently become increasingly popular in other countries. Therefore, reporting the characteristics of bodily injuries sustained by K-car drivers after road traffic accidents (RTAs) may be important not only for health professionals but also for car manufacturers.

Methods: A single-center, retrospective observational study was conducted using prospectively acquired data. Between January 2010 and December 2017, 494 restrained drivers (331 men/163 women with a mean age of 45.1 years) whose vehicles had been severely damaged in RTAs underwent whole-body computed tomography prospectively. They were subsequently dichotomized into 221 K-car drivers and 273 standard vehicle drivers and compared for severity and distribution of bodily injuries.

Results: K-car drivers tended to be older and were significantly more likely to be female than standard vehicle drivers. The frequency of subjects with severe bodily injuries significantly higher among K-car drivers than among standard vehicle drivers (21.7% vs. 14.3%; p = 0.04), and the frequency of bowel/mesentery injuries tended to be higher in the former (9.0% vs. 4.4%; p = 0.06). However, the frequency of abdominal solid viscus injuries did not differ significantly between the two groups. Multivariable regression analysis showed that age [odds ratio (OR): 1.022; 95% confidence interval (CI): 0.998-1.047; p = 0.07] and K-cars (OR: 3.708; 95% CI: 0.984-6.236; p =  0.05) tended to be associated with bowel/mesentery injuries in restrained drivers. The frequency of pelvic/hip fractures also tended to be higher in K-car drivers than in standard vehicle drivers (5.9% vs. 2.6%; p =  0.10). By contrast, the severity and frequency of the upper torso injuries were similar between the two groups.

Conclusions: Compared to standard vehicle drivers, K-car drivers seem to experience more severe bodily injuries after severe RTAs. Despite there being no answer for the increased frequency of only hollow viscus injuries but not solid viscus injuries among restrained K-car drivers, advanced age may, at least in part, be responsible. Given the limitations inherent to this study's single-center, retrospective design, multi-center prospective studies are warranted to verify our findings.