Biomechanical response of the lumbar spine in dynamic compression.

The purpose of this study was to investigate the biomechanical properties of the human lumbar spine subjected to dynamic compression. A series of six experiments using the lumbar spines from four human cadavers was performed. The first two tests utilized the entire lumbar spine while the remaining four tests used lumbar functional joints to separate the differences in stability. A high rate material testing machine was used to produce the dynamic compression at a displacement rate of 1 m/s. Custom mounting plates were developed to ensure proper anatomical position of the lumbar spine sections. Both tests with the whole lumbar spines resulted in compression fractures at T12 due to combined axial loads of 5009 N and 5911 N and bending moments of 237 Nm and 165 Nm respectively. These failures occurred as the spine behaved in first order buckling which resulted in concentrated loading and bending of the anterior aspects of the vertebral bodies. All tests with functional units resulted in endplate fractures and recorded substantially higher axial loads between 11,203 N and 13,065 N and substantially lower bending moments between 47 Nm and 88 Nm. The results indicate that the mechanical stability of the lumbar spine is critical component in relation to the tolerable compressive loads.