Significant spinal injury resulting from low-level accelerations: a case series of roller coaster injuries.

OBJECTIVES To describe a cohort of significantly injured roller coaster riders and the likely levels of acceleration at which the injuries occurred, and to compare these data with contemporary efforts to define a lower limit of acceleration below which no significant spinal injury is likely to occur. DESIGN A retrospective case series of roller coaster ride-induced significant spinal injuries. SETTING Injury incident records and emergency medical service records for the Rattler roller coaster in San Antonio, TX, were evaluated for a 19-month period in 1992 and 1993. Medical records for the more significant injuries were also reviewed and the specific injuries were tabulated, along with the demographics of the cohort. PARTICIPANTS There were 932,000 riders of the Rattler roller coaster, estimated to represent between 300,000 and 600,000 individual riders. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Injury incident reports and medical record review. RESULTS It is estimated that there were a total of 656 neck and back injuries during the study period, and 39 were considered significant by the study inclusion criteria. Seventy-two percent (28/39) of the injured subjects sustained a cervical disk injury; 71% of these injuries were at C5-6 (15 disk herniations, 5 symptomatic disk bulges) and 54% were at C6-7 (11 disk herniations, 4 symptomatic disk bulges). In the lumbar spine, the most frequent injury was a symptomatic disk bulge (20% of the cohort), followed by vertebral body compression fracture (18%), and L4-5 or L5-S1 disk herniation (13%). Accelerometry testing of passengers and train cars indicated a peak of 4.5 to 5g of vertical or axial acceleration and 1.5g of lateral acceleration over approximately 100ms (0.1s) on both. CONCLUSIONS The results of this study suggest that there is no established minimum threshold of significant spine injury. The greatest explanation for injury from traumatic loading of the spine is individual susceptibility to injury, an unpredictable variable.