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The Journal of Bone and Joint Surgery (American) 85:2184-2189 (2003)
© 2003 The Journal of Bone and Joint Surgery, Inc.

A Dynamic Study of Thoracolumbar Burst Fractures

Ruth K. Wilcox, PHD1, Thomas O. Boerger, FRCS2, David J. Allen, FRCS2, David C. Barton, PHD1, David Limb, BSC, FRCSED(ORTH)2, Robert A. Dickson, DSC2 and Richard M. Hall, PHD1

1 School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom. E-mail address for R.K. Wilcox: r.k.wilcox{at}leeds.ac.uk
2 Musculo-Skeletal Services, CSB, St. James's Hospital, Leeds LS9 7TF, United Kingdom

Investigation performed at the School of Mechanical Engineering, University of Leeds, and Musculo-Skeletal Services, St. James's Hospital, Leeds, United Kingdom

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from the Wish-bone Trust, Yorkshire Children's Spine Foundation, and the Engineering and Physical Sciences Research Council. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: The degree of canal stenosis following a thoracolumbar burst fracture is sometimes used as an indication for decompressive surgery. This study was performed to test the hypothesis that the final resting positions of the bone fragments seen on computed tomography imaging are not representative of the dynamic canal occlusion and associated neurological damage that occurs during the fracture event.

Methods: A drop-weight method was used to create burst fractures in bovine spinal segments devoid of a spinal cord. During impact, dynamic measurements were made with use of transducers to measure pressure in a synthetic spinal cord material, and a high-speed video camera filmed the inside of the spinal canal. A corresponding finite element model was created to determine the effect of the spinal cord on the dynamics of the bone fragment.

Results: The high-speed video clearly showed the fragments of bone being projected from the vertebral body into the spinal canal before being recoiled, by the action of the posterior longitudinal ligament and intervertebral disc attachments, to their final resting position. The pressure measurements in the synthetic spinal cord showed a peak in canal pressure during impact. There was poor concordance between the extent of postimpact occlusion of the canal as seen on the computed tomography images and the maximum amount of occlusion that occurred at the moment of impact. The finite element model showed that the presence of the cord would reduce the maximum dynamic level of canal occlusion at high fragment velocities. The cord would also provide an additional mechanism by which the fragment would be recoiled back toward the vertebral body.

Conclusions: A burst fracture is a dynamic event, with the maximum canal occlusion and maximum cord compression occurring at the moment of impact. These transient occurrences are poorly related to the final level of occlusion as demonstrated on computed tomography scans.

Clinical Relevance: In a thoracolumbar burst fracture, the final position of the fragments, as seen on computed tomography images at presentation, probably does not represent the maximum level of canal occlusion or peak cord pressure and therefore does not represent the probable damage to the cord tissue that occurred at the moment of impact.


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