Occlusion of the lumbar spine canal during high-rate axial compression.

Abstract

While burst fracture is a well-known cause of spinal canal occlusion with dynamic, axial spinal compression, it is unclear how such loading mechanisms might cause occlusion without fracture. To determine how spinal canal occlusion during dynamic compression of the lumbar spine is differentially caused by fracture or mechanisms without fracture and to examine the influence of spinal level on occlusion. A cadaveric biomechanical study. Twenty sets of three-vertebrae specimens from all spinal levels between T12 and S1 were subjected to dynamic compression using a hydraulic loading apparatus up to a peak velocity between 0.1 and 0.9 m/s. The presence of canal occlusion was measured optically with a high-speed camera. This was repeated with incremental increases of 4% compressive strain until a vertebral fracture was detected using acoustic emission measurements and computed tomographic imaging. For axial compression without fracture, the peak occlusion (O_max) was 29.9±10.0%, which was deduced to be the result of posterior bulging of the intervertebral disc into the spinal canal. O_max correlated significantly with lumbar spinal level (p<.001), the compressive displacement (p<.001) and the cross-sectional area of the vertebra (p=.031). Spinal canal occlusion observed without vertebral fracture involves intervertebral disc bulging. The lower lumbar spine tended to be more severely occluded than more proximal levels. Clinically, intermittent canal occlusion from disc bulging during dynamic compression may not show any radiographic features. The lower lumbar spine should be a focus of injury prevention intervention in cases of high-rate axial compression.