gms | German Medical Science

54. Jahrestagung der Norddeutschen Orthopädenvereinigung e. V.

Norddeutsche Orthopädenvereinigung

16.06. bis 18.06.2005, Hamburg

Segmental spine stability after pedicle screw loosening

Meeting Abstract

  • corresponding author O. Diedrich - Rheinische Friedrich-Wilhelms Universität zu Bonn, Klinik und Poliklinik für Orthopädie, Bonn
  • C.N. Kraft - Bonn
  • C. Lühring - Bad Abbach
  • L. Perlick - Bad Abbach
  • P. Pennekamp - Bonn

Norddeutsche Orthopädenvereinigung. 54. Jahrestagung der Norddeutschen Orthopädenvereinigung e.V.. Hamburg, 16.-18.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05novW3.04

Die elektronische Version dieses Artikels ist vollständig und ist verfügbar unter: http://www.egms.de/de/meetings/nov2005/05nov042.shtml

Veröffentlicht: 13. Juni 2005

© 2005 Diedrich et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielf&aauml;ltigt, verbreitet und &oauml;ffentlich zug&aauml;nglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Introduction

In spinal surgery postoperative failure of pedicle screw instrumentation due to loosening of the implant at the bone-screw interface is a clinically relevant problem. While there are numerous biomechanical studies dealing with stability after internal fixation, little is known about the remaining segmental stability after pedicle screw loosening.

Methods

Motion analysis was performed on intact (controls) and posterior monosegmental L5/6 destabilized lumbar spines of sheep. Primary insertion of the conical pedicle screws was performed with a torque of 1,4 Nm. Pedicle screw loosening was simulated by turning the inserted screw back either 180° or 540°. Specimens instrumented with screws of differing diameter as well as non-instrumented pedicles were also compared.

Results

Independent of the type of instrumentation, we found a significant increase of motion in the instrumented segment with increasing screw loosening compared to firmly inserted screws. Matched against sole pedicle screw instrumentation, 360° internal fixation showed significantly less motion when screws were loosened by 180° and 540°. In cases where loosened 5,5 mm screws were changed in favor of 6,7 mm screws, a high stability comparable to that initially measured was regained, independent of the type of fixation-method. 5,5 mm screws that were inserted in widened pedicles showed a marked decrease of primary segmental stability.

Conclusion

The biomechanical advantages after 360° segmental lumbar instrumentation compared to isolated pedicle screw instrumentation are well documented. This study suggests, that concerning the remaining stability, 360° instrumentation is also superior in cases where pedicle screw loosening has occurred.