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

The electronic version of this article is the complete one and can be found online at:

Published: June 13, 2005

© 2005 Diedrich et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.




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.


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.


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.


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.