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Publisher DOI: 10.1007/s00586-020-06593-3
Title: Cortical threaded pedicle screw improves fatigue strength in decreased bone quality
Language: English
Authors: Weiser, Lukas 
Sellenschloh, Kay 
Püschel, Klaus 
Morlock, Michael 
Viezens, Lennart 
Lehmann, Wolfgang 
Huber, Gerd 
Keywords: BMD; Osteoporosis; Pedicle screw design; Pedicle screw loosening; Spine
Issue Date: 2021
Publisher: Springer
Source: European Spine Journal 1 (30): 128-135 (2021-01)
Abstract (english): 
Purpose: Inadequate anchoring of pedicle screws in vertebrae with poor bone quality is a major problem in spine surgery. The aim was to evaluate whether a modified thread in the area of the pedicle could significantly improve the pedicle screw fatigue strength.

Methods: Fourteen human cadaveric vertebral bodies (L2 and L3) were used for in vitro testing. Bone density (BMD) was determined by quantitative computed tomography. Vertebral bodies were instrumented by standard pedicle screws with a constant double thread on the right pedicle and a partial doubling of the threads–quad thread–(cortical thread) in the area of the pedicle on the left pedicle. Pulsating sinusoidal, cyclic load (0.5 Hz) with increasing peak force (100 N + 0.1 N/cycles) was applied orthogonal to the screw axis. The baseline force remained constant (50 N). Fatigue test was terminated after exceeding 5.4-mm head displacement (~ 20° screw tilting).

Results: The mean fatigue load at failure was 264.9 N (1682 cycles) for the standard screws and was increased significantly to 324.7 N (2285 cycles) by the use of cortical threaded screws (p = 0.014). This effect is particularly evident in reduced BMD (standard thread 241.2 N vs. cortical thread 328.4 N; p = 0.016), whereas in the group of vertebrae with normal BMD no significant difference could be detected (standard thread 296.5 N vs. cortical thread 319.8 N; p = 0.463).

Conclusions: Compared to a conventional pedicle screw, the use of a cortical threaded pedicle screw promises superior fatigue load in vertebrae with reduced bone quality.
DOI: 10.15480/882.3293
ISSN: 0940-6719
Journal: European spine journal 
Institute: Biomechanik M-3 
Document Type: Article
More Funding information: Open Access funding enabled and organized by Projekt DEAL.
License: CC BY 4.0 (Attribution) CC BY 4.0 (Attribution)
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