The biomechanical responses of 48 lumar motion segments exposed to loads similar to those in frontal car accidents were determined by means of a new method of applying dynamic (transient) flexion-shear loads. The applied loads caused flexion - distraction injuries in the specimens, so-called lap seat belt injuries. The peak values of the applied load pulses in the present experiments varied between 5-12 g, with a rise time between 5-30 ms and a duration between 150-250 ms. The specimens could withstand loads up to 225 Nm and 720 N in flexion before obvious fractures occurred. Signs of injury in the bony structure were observed at lower load levels. The results showed that the magnitude of the applied load pulse and the loading rate determined the degree and severity of spinal injury. The duration of the load pulse did not affect the load and injury response. The specimens could withstand higher loads and absorb more energy when the loading rate was increased, but the deformations at injury were smaller when the loading rate was high. The biological parameters bone mineral content, anterior-posterior length and height of the specimen showed high correlations with the dynamic load response of the lumbar spine.
Abstract