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Eur Spine J (2013) 22:4653 DOI 10.1007/s00586-012-2461-2
ORIGINAL ARTICLE
Comparison of revision strategies for failed C2-posterior cervical pedicle screws: a biomechanical study
Michael Mayer Juliane Zenner Robert Bogner Wolfgang Hitzl
Markus Figl Arvind von Keudell Daniel Stephan Rainer Penzkofer
Peter Augat Gundobert Korn Herbert Resch Heiko Koller
Received: 7 September 2011 / Revised: 13 May 2012 / Accepted: 24 July 2012 / Published online: 28 August 2012 Springer-Verlag 2012
AbstractStudy purpose With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs.
Materials and methods Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion
accuracy was veried by uoroscopy. C2 vertebrae were potted and xed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%).
Results The POR of primary 3.5-mm CPSs was 1,140.5 539.6 N for Group-1 and 1,007.7 362.5 N for Group-2; the difference was not signicant. In the revision setting, the POR in Group-1 was 705.8 449.1 N, representing a reduction of 38.1 32.9 % compared with that of primary screw xation. For Group-2, the POR was 875.3 367.9 N, representing a reduction of 13.1 23.4 %. A statistical analysis showed a signicantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a signicantly reduced POR for both revision strategies compared with primary xation (p \ 0.001/
p = 0.001), the loss of POR (in %) in Group-1 was...