The Comparison of Pullout Strengths of Various Pedicle Screw Designs on Synthetic Foams and Ovine Vertebrae.

AIM One of the most common problems with transpedicular screws is screw pullout. This study was conducted to measure the pullout strengths of newly designed transpedicular screws. MATERIAL AND METHODS The design of the three group screws were conical cored standard pedicle screw (Type A), dual threaded pedicle screw (Type B), dual core and dual threaded pedicle screw (Type C), respectively. Polyurethane (PU) blocks in 25 mm and 50 mm thickness were used to investigate the effect of just the pedicle on pullout strength and both distal (vertebral body) and proximal (pedicle) parts of the screw. The screws were also tested in ovine lumbar vertebrae. RESULTS Type C screw exhibited 5.9% and 12.9% higher pullout strength than Type A and Type B, and 15.4% and 8.6% higher pullout strength than Type A and Type B, respectively on 25 mm and 50 mm thick PU foam block. Type C also exhibited 74.5% and 22.5% higher pullout strength than Type A and Type B, respectively on the ovine vertebrae. CONCLUSION Transpedicular screws redesigned with modified helical angles exhibit higher pullout strength compared to the classical transpedicular screws and can be inserted more rapidly with the same number of screwing rounds result with doubled insertion depth.

[1]  N. Crawford,et al.  Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines. , 2013, The spine journal : official journal of the North American Spine Society.

[2]  W. McGarry,et al.  A titanium expandable pedicle screw improves initial pullout strength as compared with standard pedicle screws. , 2011, The spine journal : official journal of the North American Spine Society.

[3]  Zi-xiang Wu,et al.  Biomechanical and histological evaluation of an expandable pedicle screw in osteoporotic spine in sheep , 2010, European Spine Journal.

[4]  D. Shin,et al.  Serious Complication of Cement Augmentation for Damaged Pilot Hole , 2010, Yonsei medical journal.

[5]  J. Torner,et al.  Biomechanical comparison of single- and dual-lead pedicle screws in cadaveric spine. , 2008, Journal of neurosurgery. Spine.

[6]  J. Goldhahn,et al.  Mechanical performance of cylindrical and dual core pedicle screws in calf and human vertebrae , 2006, Archives of Orthopaedic and Trauma Surgery.

[7]  C. Chao,et al.  Increase of pullout strength of spinal pedicle screws with conical core: Biomechanical tests and finite element analyses , 2005, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[8]  G. Andersson,et al.  Augmentation of Pedicle Screw Fixation Strength Using an Injectable Calcium Phosphate Cement as a Function of Injection Timing and Method , 2004, Spine.

[9]  W. Walsh,et al.  Hydroxyapatite Composite Resin Cement Augmentation of Pedicle Screw Fixation , 2003, Clinical orthopaedics and related research.

[10]  S. Evans,et al.  Bone cement or bone substitute augmentation of pedicle screws improves pullout strength in posterior spinal fixation , 2002, Journal of materials science. Materials in medicine.

[11]  A. Valdevit,et al.  Characteristics of pullout failure in conical and cylindrical pedicle screws after full insertion and back-out. , 2001, The spine journal : official journal of the North American Spine Society.

[12]  T Suzuki,et al.  Improving the pullout strength of pedicle screws by screw coupling. , 2001, Journal of spinal disorders.

[13]  S. Cook,et al.  Lumbosacral fixation using expandable pedicle screws. an alternative in reoperation and osteoporosis. , 2001, The spine journal.

[14]  K. Okuyama,et al.  Can insertional torque predict screw loosening and related failures? An in vivo study of pedicle screw fixation augmenting posterior lumbar interbody fusion. , 2000, Spine.

[15]  F. Dikici,et al.  Pedicle screw salvage: the effect of depth and diameter on pull-out strength: a biomechanical study , 2000 .

[16]  B. Bai,et al.  The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures. , 1999, Spine.

[17]  R. Ellenbogen,et al.  Revision Pedicle Screws: Bigger, Longer Shims‐What Is Best? , 1998, Spine.

[18]  T C Hearn,et al.  Insertional Torque and Pull‐out Strengths of Conical and Cylindrical Pedicle Screws in Cadaveric Bone , 1996, Spine.

[19]  B. Myers,et al.  The Role of Imaging and In Situ Biomechanical Testing in Assessing Pedicle Screw Pull‐Out Strength , 1996, Spine.

[20]  W C Hutton,et al.  Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws. , 1994, Journal of spinal disorders.

[21]  C. Dickman,et al.  Transpedicular screw-rod fixation of the lumbar spine: operative technique and outcome in 104 cases. , 1992, Journal of neurosurgery.

[22]  E. Transfeldt,et al.  Experimental Pullout Testing and Comparison of Variables in Transpedicular Screw Fixation: A Biomechanical Study , 1990, Spine.