Biomechanical Evaluation of a Double-Threaded Pedicle Screw in Elderly Vertebrae

We sought to test the hypothesis that a pedicle screw that has two parallel threads of different heights throughout the full length of the screw could increase both bone purchase and pullout strength compared with a standard single-threaded screw of similar dimensions. A single-threaded pedicle screw and a double-threaded pedicle screw were respectively placed into the paired pedicles of 21 vertebral bodies. The screws were then pulled out of the pedicles, and output parameters were measured. Although insertional torque was, on average, 14.5% higher (p = 0.039) for the single-threaded screw, maximum pullout strength (p = 0.12), energy-to-failure (p = 0.39), and stiffness (p = 0.54) were not statistically different for the two screw types. It is concluded that a second, smaller inner thread on a double-threaded pedicle screw does not translate into either increased bone purchase or higher pullout strengths.

[1]  K. Kumano,et al.  Reduction of lumbar spondylolisthesis using a CDI pedicle screw system , 2004, Archives of Orthopaedic and Trauma Surgery.

[2]  N. Ordway,et al.  Characteristics of unicortical and bicortical lateral mass screws in the cervical spine. , 1999, Spine.

[3]  V. Sonntag,et al.  Efficacy of pedicle screw fixation in the treatment of spinal instability and failed back surgery: a 5-year review. , 1998, Journal of neurosurgery.

[4]  R. Yeasting,et al.  Anatomic Considerations of Pedicle Screw Placement in the Thoracic Spine: Roy‐Camille Technique Versus Open‐Lamina Technique , 1998, Spine.

[5]  T. Washio,et al.  Structural Characteristics of the Pedicle and Its Role in Screw Stability , 1997, Spine.

[6]  R. N. Kruse,et al.  Mechanical Stability of Thoracolumbar Pedicle Screw Fixation: The Effect of Crosslinks , 1997, Spine.

[7]  T. Washio,et al.  An Experimental Study of a Combination Method Using a Pedicle Screw and Laminar Hook for the Osteoporotic Spine , 1997, Spine.

[8]  P. Mccormick.  Selection criteria for degenerative lumbar spine instability. , 1997, Clinical neurosurgery.

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

[10]  V K Goel,et al.  Effect of Specimen Fixation Method on Pullout Tests of Pedicle Screws , 1996, Spine.

[11]  S. Cook,et al.  Effects of Bone Mineral Density on Pedicle Screw Fixation , 1994, Spine.

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

[13]  W. Hayes,et al.  Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. , 1993, Clinical orthopaedics and related research.

[14]  D N Kunz,et al.  Pedicle Screw Pullout Strength: Correlation with Insertional Torque , 1993, Spine.

[15]  T C Hearn,et al.  Biomechanical Testing of a New Design for Schanz Pedicle Screws , 1993, Journal of orthopaedic trauma.

[16]  K. Murota,et al.  An Experimental Study on Transpedicular Screw Fixation in Relation to Osteoporosis of the Lumbar Spine , 1991, Spine.

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

[18]  G. Sammarco,et al.  Metatarsal Osteotomy Using a Double-Threaded Compression Scew: An Adjunct to Revision Forefoot Surgery , 1989, Foot & ankle.

[19]  J. Moran,et al.  Transpedicular screw fixation , 1989, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[20]  J W Frymoyer,et al.  An internal fixator for posterior application to short segments of the thoracic, lumbar, or lumbosacral spine. Design and testing. , 1986, Clinical orthopaedics and related research.

[21]  B. T. Field,et al.  A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine. , 1986, Clinical orthopaedics and related research.

[22]  T. Herbert,et al.  Management of the fractured scaphoid using a new bone screw. , 1986, The Journal of bone and joint surgery. British volume.

[23]  F. Magerl.  Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. , 1984, Clinical orthopaedics and related research.

[24]  S. Sijbrandij.  Reduction and stabilisation of severe spondylolisthesis. A report of three cases. , 1983, Journal of Bone and Joint Surgery-british Volume.

[25]  J. Schatzker,et al.  The holding power of orthopedic screws in vivo. , 1975, Clinical orthopaedics and related research.

[26]  E. F. Byars,et al.  EFFECT OF EMBALMING ON THE MECHANICAL PROPERTIES OF BEEF BONE. , 1964, Journal of applied physiology.