Document Detail

The effect of design parameters of dynamic pedicle screw systems on kinematics and load bearing: an in vitro study.
MedLine Citation:
PMID:  21110209     Owner:  NLM     Status:  MEDLINE    
As an alternative treatment for chronic back pain due to disc degeneration motion preserving techniques such as posterior dynamic stabilization (PDS) has been clinically introduced, with the intention to alter the load transfer and the kinematics at the affected level to delay degeneration. However, up to the present, it remains unclear when a PDS is clinically indicated and how the ideal PDS mechanism should be designed to achieve this goal. Therefore, the objective of this study was to compare different PDS devices against rigid fixation to investigate the biomechanical impact of PDS design on stabilization and load transfer in the treated and adjacent cranial segment. Six human lumbar spine specimens (L3-L5) were tested in a spine loading apparatus. In vitro flexibility testing was performed by applying pure bending moments of 7.5 Nm without and with additional preload of 400 N in the three principal motion planes. Four PDS devices, "DYN" (Dynesys(®), Zimmer GmbH, Switzerland), "DSS™" (Paradigm Spine, Wurmlingen, Germany), and two prototypes of dynamic rods, "LSC" with a leaf spring, and "STC" with a spring tube (Aesculap AG, Tuttlingen, Germany), were tested in comparison to a rigid fixation device S(4) (Aesculap AG, Tuttlingen, Germany) "RIG", to the native situation "NAT" and to a defect situation "DEF" of the specimens. The instrumented level was L4-L5. The tested PDS devices comprising a stiffness range for axial stiffness of 10 N/mm to 230 N/mm and for bending stiffness of 3 N/mm to 15 N/mm. Range of motion (ROM), neutral zone (NZ), and intradiscal pressure (IDP) were analyzed for all instrumentation steps and load cases of the instrumented and non-instrumented level. In flexion, extension, and lateral bending, all systems, except STC, showed a significant reduction of ROM and NZ compared to the native situation (p < 0.05). Furthermore, we found no significant difference between DYN and RIG (p > 0.1). In axial rotation, only DSS and STC reduced the ROM significantly (p < 0.005) compared to the native situation, whereas DYN and LSC stayed at the level of the native intersegmental rotation (p > 0.05). A correlation was found between axial stiffness and intersegmental stabilization in the sagittal and frontal plane, but not in the transversal plane where intersegmental stabilization is mainly governed by the systems' ability to withstand shear loads. Furthermore, we observed the systems' capacity to reduce IDP in the treated segment. The adjacent segment does not seem to be affected by the stiffness of the fixation device under the described loading conditions.
C Schilling; S Krüger; T M Grupp; G N Duda; W Blömer; A Rohlmann
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Publication Detail:
Type:  Journal Article     Date:  2010-11-26
Journal Detail:
Title:  European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society     Volume:  20     ISSN:  1432-0932     ISO Abbreviation:  Eur Spine J     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2011-01-31     Completed Date:  2011-06-30     Revised Date:  2013-07-03    
Medline Journal Info:
Nlm Unique ID:  9301980     Medline TA:  Eur Spine J     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  297-307     Citation Subset:  IM    
Research and Development, Biomechanical Research, Aesculap AG, Am Aesculap Platz, 78532, Tuttlingen, Germany.
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MeSH Terms
Biomechanics / physiology
Bone Screws*
Internal Fixators
Lumbar Vertebrae / physiology,  surgery*
Middle Aged
Orthopedic Procedures / instrumentation*,  methods
Range of Motion, Articular
Weight-Bearing / physiology

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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