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Risk of injuries increased by improper use of seatbelts   Using automatic shoulder belt systems without using manual lap belts, while better than no restraint use, is associated with an increased risk of serious chest and abdominal injuries, according to a recent article in The Journal of the American Medical Association (JAMA).   Frederick P. Rivara, M.D., MPH, and colleagues from Harborview Injury Prevention and Research Center, Seattle, examined the relationship between automatic shoulder belt systems and risk of injury and death among front-seat passenger vehicle occupants.   The authors analyzed data from the 1993-1996 National Highway Traffic Safety Administration Crashworthiness Data System on front-seat occupants involved in 25,811 tow-away crashes of passenger cars, light trucks, vans, and sport utility vehicles. Among these occupants, 21.9 percent were unrestrained, 60.3 percent were restrained with a manual three-point system, 15.1 percent were restrained with an automatic shoulder belt and a manual automatic lap belt, and 2.7 percent were using an automatic shoulder belt without the lap belt.   The researchers found that users of automatic shoulder belts without lap belts had a risk of head injury in all crashes and in frontal crashes that was not significantly different from that of unbelted occupants, but had a 2.7-fold higher risk of chest injury in all crashes and more than 7-fold higher risk of chest injury in frontal crashes compared with no belt use.    The researchers also found similar patterns in relation to risk of abdominal injury with the risk of injury 2-fold higher in all crashes and more than 3.7-fold higher in frontal crashes. Based on the data, the researchers found there was no significant difference between restraint systems in the risk of injuries to the spine or the extremities.   According to background information in the article, various strategies have been developed to improve motor vehicle occupant protection, including an automatic shoulder belt, combined with a manual lap belt. Since 1987 more than 27 million cars have been manufactured with automatic 2-point belt systems, with more than 10 million still in use. Previous studies found that 50 percent to 71 percent of drivers do not use the manual lap belt.   The authors also found that the use of automatic shoulder belts without lap belts was associated with a decreased  risk of death compared with no restraint use.    The authors conclude that, “given the still widespread use of these automatic systems, educational programs that encourage vehicle occupants to buckle up their lap belts may be warranted.”