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The Influence of Distraction Force on the Intradiscal Pressure Gradient in the Bridged Lumbar Spine: A Biomechanical Investigation Using a Calf Model

Spiegl, Ulrich MD*; Pätzold, Robert MD†,‡; Glasmacher, Stefan MD*; Stephan, Daniel PhD*,§; Josten, Christoph Prof.*; Bühren, Volker Prof.; Gonschorek, Oliver MD; Augat, Peter‡,§

doi: 10.1097/BRS.0000000000000213

Study Design. A biomechanical calf cadaver study.

Objective. The purpose of this study was to determine the intradiscal pressure gradient of bridged healthy intervertebral segments in correlation with intraoperative distraction force.

Summary of Background Data. Bisegmental dorsal stabilization and anatomic reduction is a common treatment option for incomplete burst fractures of the lumbar spine. However, it remains unknown to what extent bridging and intraoperative distraction compromises an intact intervertebral disc.

Methods. The L2–L3 intervertebral disc level was evaluated in 6 freshly frozen calf cadaver spines. Pressure measurements were obtained with the spine uninstrumented, after dorsal segmental instrumentation from L1 to L3, and after distraction with 400 N and 800 N. Pressure gradient measurements were accomplished with a balloon pressure sensor placed within the nucleus pulposus of the L2–L3 intervertebral disc. Pressure data were recorded by computer data acquisition. Flexion, extension, and lateral bending moments were applied continuously by a testing machine up to a load moment of 7.5 N·m. The pressure gradients were compared with respect to the effects of added instrumentation and distraction.

Results. After segmental bridging the mean pressure gradients were significantly reduced in all movement directions (P < 0.001). However, after dorsal stabilization a continuously rising intervertebral disc pressure was recordable. In contrast, no relevant additional reduction of the intradiscal pressure gradient was detectable after applying distraction forces of 400 N or 800 N.

Conclusion. In a calf model, a distraction force of up to 800 N leads to no additional reduction of the pressure gradient of bridged healthy lumbar segments under flexion and extension moments.

Level of Evidence: N/A

The aim of this study was to evaluate the effect of distraction on intradiscal pressure in bridged healthy intervertebral lumbar discs. After segmental bridging fixation, we observed a significant reduction of the intradiscal pressure under flexion and lateral bending loads. No further change in the pressure gradients was visible under distraction force of 800 N.

*Department of Trauma and Reconstructive Surgery, Spine Center, University of Leipzig, Germany

BG Trauma Center, Murnau, Germany

Institute of Biomechanics, BG Trauma Center, Murnau, Germany; and

§Institute of Biomechanics, Paracelsus Medical University Salzburg, Austria.

Address correspondence and reprint requests to Ulrich Spiegl, MD, University of Leipzig, Department of Trauma and Reconstructive Surgery, Spine Center, Liebigstr. 20, 04103 Leipzig, Germany; E-mail:

Acknowledgment date: August 8, 2013. Revision date: December 19, 2013. Acceptance date: December 27, 2013.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work.

Relevant financial activities outside the submitted work: consultancy, grants.

© 2014 by Lippincott Williams & Wilkins