Complex sentence: Pediatric trauma accounted for 59.5% of all mortality for children under 18 in 2004, injury is the leading cause of death in this age group in the United States--more than all other causes combined.
Split into simpler sentences: Pediatric trauma accounted for 59.5% of all mortality for children under 18 in 2004. Injury is the leading cause of death in this age group in the United States--more than all other causes combined.