• Ulrich Spiegl, Robert Pätzold, Stefan Glasmacher, Daniel Stephan, Christoph Josten, Volker Bühren, Oliver Gonschorek, and Peter Augat.
• *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.
• Spine. 2014 Apr 1;39(7):E427-33.

Study DesignA biomechanical calf cadaver study.ObjectiveThe 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 DataBisegmental 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.MethodsThe 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.ResultsAfter 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.ConclusionIn 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.

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