The influence of distraction force on the intradiscal pressure gradient in the bridged lumbar spine: a biomechanical investigation using a calf model.
METHODS
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.


BACKGROUND
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.


CONCLUSIONS
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.
*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.
Ulrich
U
Spiegl
Robert
R
Pätzold
Stefan
S
Glasmacher
Daniel
D
Stephan
Christoph
C
Josten
Volker
V
Bühren
Oliver
O
Gonschorek
Peter
P
Augat
D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D007403:Intervertebral Disc / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D023421:Models, Animal; D009068:Movement / Q000502:physiology; D011187:Posture / Q000502:physiology; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology