Lukas Weiser1, Kay Sellenschloh2, Klaus Püschel3, Michael M Morlock2, Lennart Viezens4, Wolfgang Lehmann4, Gerd Huber2. 1. Department of Trauma Surgery, Orthopaedic Surgery and Plastic Surgery, University Medical Center Göttingen, Robert-Koch-Str. 40, 37099, Göttingen, Germany. Lukas.Weiser@med.uni-goettingen.de. 2. Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany. 3. Institute of Forensic Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. 4. Department of Trauma Surgery, Orthopaedic Surgery and Plastic Surgery, University Medical Center Göttingen, Robert-Koch-Str. 40, 37099, Göttingen, Germany.
Abstract
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.
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.
Authors: Odysseas Paxinos; Parmenion P Tsitsopoulos; Michael R Zindrick; Leonard I Voronov; Mark A Lorenz; Robert M Havey; Avinash G Patwardhan Journal: J Neurosurg Spine Date: 2010-10
Authors: Lukas Weiser; Gerd Huber; Kay Sellenschloh; Lennart Viezens; Klaus Püschel; Michael M Morlock; Wolfgang Lehmann Journal: Eur Spine J Date: 2017-04-08 Impact factor: 3.134
Authors: Michael G Fehlings; Branko Kopjar; Ahmed Ibrahim; Lindsay A Tetreault; Paul M Arnold; Helton Defino; Shashank Sharad Kale; S Tim Yoon; Giuseppe M Barbagallo; Ronald H M Bartels; Qiang Zhou; Alexander R Vaccaro; Mehmet Zileli; Gamaliel Tan; Yasutsugu Yukawa; Darrel S Brodke; Christopher I Shaffrey; Osmar Santos de Moraes; Eric J Woodard; Massimo Scerrati; Masato Tanaka; Tomoaki Toyone; Rick C Sasso; Michael E Janssen; Ziya L Gokaslan; Manuel Alvarado; Ciaran Bolger; Christopher M Bono; Mark B Dekutoski Journal: Spine J Date: 2017-09-06 Impact factor: 4.166