Study objective: This study estimates trends in impairment before and after the 1992 California Mandatory Helmet Use Law using the injury impairment Scale (IIS).
Methods: We linked medical records and police reports for a cohort of 4,790 nonfatally injured motorcycle riders who crashed between January 1, 1991, and December 31, 1993, and were treated for injuries in 1 of 18 hospitals in 10 California counties. All injuries were coded according to the Abbreviated Injury Scale and matched to corresponding codes in the IIS. The IIS provides an estimate of the likelihood of impairment from any given injury. Impairment is not directly measured.
Results: After implementation of the law, the proportion of riders likely to sustain head injury-related impairments decreased by 34.1%. Impairments resulting from head injuries were the most common type before passage of the law, but they were surpassed by leg injury-related impairments after passage. Helmet nonuse, speeding, and drinking were among variables associated with increased odds ratios of head injury estimated to cause impairment.
Conclusion: The proportion of motorcycle riders with head injury impairment as estimated with the IIS decreased significantly after the introduction of mandatory motorcycle helmet legislation.