Why do Femur Fractures Occur in Relatively Low-Velocity Frontal Car Crashes?
Allan F. Tencer, PhD; Rob Kaufman, BSc; K. Ryan; David Grossman, MD; M. Bradford Henley, MD; F. Mann; C. Mock; F. Rivara, University of Washington, Seattle, WA (all authors a-National Highway Traffic Safety Administration, US Department of Transportation) Introduction: Femur fractures are a common occurrence in frontal motor vehicle collisions, usually resulting from axial compression and bending loads caused by direct contact of the occupant’s knees with the knee bolster (the energy absorbing stiffener behind the dashboard). Knee-to-knee bolster contact reduces the force of the shoulder belt against the occupant’s chest. In standardized frontal crash tests at 55 kph (35 mph) (New Car Assessment Program, U.S. Department of Transportation), the femoral forces recorded by crash dummies are required to fall below the estimated fracture strength of the femur, about 8900 N. However, in a sample of frontal crashes that we investigated, with speed changes about 40 kph (25 mph), the only maj
