Oral Presentation ANZBMS-MEPSA-ANZORS 2022

Lumbar spinal canal occlusion due to bulging of intervertebral disc (#80)

Dale L Robinson 1 , Melanie Franklyn 2 , David C Ackland 1 , Peter Vee Sin Lee 1
  1. University of Melbourne, Parkville, VIC, Australia
  2. Defence Science and Technology Group, Melbourne, VIC, Australia

During spinal fractures, occlusion of the spinal canal presents a high risk of neurological deficit due to bone fragments being retropulsed into the canal. There is evidence that bulging of the intervertebral disc can also result in neurological compression [1], yet no previous studies have examined how this alternative mechanism in detail. For example, it is unclear to what extent the spinal canal may be occluded by the disc or whether occlusion is influenced by morphometric variation. These questions are relevant to understanding spinal injuries encountered in military scenarios, where there are disproportionately high rates of spinal injuries below the thoracolumbar junction. The aim of this study was to quantify how lumbar spine canal occlusion induced by disc bulging is influenced by vertebral fracture or morphometic variation between different spinal positions.

Twenty sets of three-vertebra specimens with centre vertebra encompassing L1 to L5 were compressed at 1m/s. Canal occlusion was measured optically with a high-speed camera (Figure 1). The compression test was repeated with incremental increases in displacement until a bone fracture was identified using acoustic emission sensors and computed tomographic imaging. For axial compression prior to fracture, the peak occlusion was 29.9+/-10.0%, which was deduced to result from posterior bulging of the intervertebral disc. The maximum occlusion correlated significantly with lumbar spinal level (p<.001) and the cross-sectional area of the vertebra (p=.031). It may be concluded that disc bulging can cause significant amounts of lumbar spinal canal occlusion, which is more severe at distal levels. This finding is of clinical relevance because occlusion from disc bulging may not be apparent radiographically. Further, the lower lumbar spine's greater susceptibility to occlusion suggests that this location ought to be the focus of new injury mitigation technologies in situations at risk of high-rate axial compression.

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Figure 1: Experimental setup

 

  1. [1] Fredericson M, et al. Spine J 2001;1(1):10–7.