Advantage of Pedicle Screw Fixation Directed Into the Apex of the Sacral Promontory Over Bicortical Fixation: A Biomechanical Analysis

Study Design. A biomechanical study of human cadaveric sacra using insertional torque and bone mineral density was conducted to determine the optimal sagittal trajectory of S1 pedicle screws. Objective. To measure the maximal insertional torque of sacral promontory versus bicortical pedicle screw fixation. Summary of Background Data. Fixation of instrumentation to the sacrum is commonly accomplished using S1 pedicle screws, with previous studies reporting biomechanical advantages of bicortical over unicortical S1 screws. The biomechanical effect of bicortical screws (paralleling the endplate) versus screws directed into the apex of the sacral promontory is unknown. Methods. For this study, 10 fresh frozen cadaver sacra were harvested and evaluated with dual-energy radiograph absorptiometry to assess bone mineral density. Matched 7.5-mm monoaxial stainless steel pedicle screws then were randomly assigned by side (left versus right) and placed bicortically or into the apex of the sacral promontory under direct visualization. Maximum insertional torque was recorded for each screw revolution with a digital torque wrench (TQJE1500, Snap-On Tools, Kenosha, WI). Results. Maximum bicortical S1 screw insertional torque averaged 5.22 ± 0.83 inch-pounds, as compared with the maximum sacral promontory S1 screw insertional torque of 10.34 ± 1.94 inch-pounds. This resulted in a 99% increase in maximum insertional torque (P = 0.005) using the “tricortical” technique, with the screw directed into the sacral promontory. Mean bone mineral density was 940 ± 0.25 mg/cm2 (range, 507–1428 mg/cm2). The bone mineral density correlated with maximal insertional torque for the sacral promontory technique (r = 0.806;P = 0.005), but not for the bicortical technique (r = 0.48;P = 0.16). Conclusions. The screws directed into the apex of the sacral promontory of the S1 pedicle resulted in an average 99% increase in peak insertional torque (P = 0.005), as compared with bicortical S1 pedicle screw fixation. Tricortical pedicle screw fixation correlates directly with bone mineral density.

[1]  J. Leong,et al.  Variation in Bone Mineral Density of the Sacrum in Young Adults and Its Significance for Sacral Fixation , 2000, Spine.

[2]  L. Plank,et al.  Pedicle screw placement at the sacrum: anatomical characterization and limitations at S1. , 1999, Journal of spinal disorders.

[3]  J. Leong,et al.  Comparison of the Strengths of Lumbosacral Fixation Achieved With Techniques Using One and Two Triangulated Sacral Screws , 1998, Spine.

[4]  A. Valdevit,et al.  Biomechanical Testing of the Lumbosacral Spine , 1998, Spine.

[5]  M. Krismer,et al.  Comparison Between Single‐Screw and Triangulated, Double‐Screw Fixation in Anterior Spine Surgery: A Biomechanical Test , 1996, Spine.

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

[7]  J. Lotz,et al.  Biomechanical Analysis of Lumbosacral Fixation , 1996, Spine.

[8]  E. Benzel,et al.  Sacral fixation using iliac instrumentation and a variable-angle screw device. Technical note. , 1994, Journal of neurosurgery.

[9]  Per-Lee Jh.  Techniques of instrumentation in long fusions to the sacrum. , 1994 .

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

[11]  R. Kruse,et al.  Lumbar and lumbosacral fusion using Steffee instrumentation. , 1994, Spine.

[12]  R. Haid,et al.  Lumbar and lumbosacral fusions using Cotrel-Dubousset pedicle screws and rods. , 1994, Spine.

[13]  J. Perra.  Techniques of instrumentation in long fusions to the sacrum. , 1994, The Orthopedic clinics of North America.

[14]  D. Bradford,et al.  Sacral screw loads in lumbosacral fixation for spinal deformity. , 1993, Spine.

[15]  K Okuyama,et al.  Stability of transpedicle screwing for the osteoporotic spine. An in vitro study of the mechanical stability. , 1993, Spine.

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

[17]  R. Jackson,et al.  The Iliac Buttress: A Computed Tomographic Study of Sacral Anatomy , 1993, Spine.

[18]  S. Garfin,et al.  The effects of depth of penetration, screw orientation, and bone density on sacral screw fixation. , 1993, Spine.

[19]  L. Ross,et al.  Pitfalls of Pedicle Screw Fixation in the Sacrum: A Cadaver Model , 1992, Spine.

[20]  S. Garfin,et al.  Screw Fixation in the Human Sacrum: An In Vitro Study of the Biomechanics of Fixation , 1992, Spine.

[21]  S. Glassman,et al.  Technique and Results of Fixation to the Sacrum with Iliosacral Screws , 1992, Spine.

[22]  O. Boachie-Adjei,et al.  Surgical treatment of neuropathic spinal arthropathy. , 1991, Journal of spinal disorders.

[23]  P. McAfee,et al.  Survivorship Analysis of Pedicle Spinal Instrumentation , 1991, Spine.

[24]  D. Spencer,et al.  The Use of Sublaminar Cables to Replace Luque Wires , 1991, Spine.

[25]  W. Rauschning,et al.  Surgical Anatomy of the Sacrum: A Guide for Rational Screw Fixation , 1991, Spine.

[26]  J. Massie,et al.  Anatomic Consideration for Sacral Screw Placement , 1991, Spine.

[27]  O. Boachie-Adjei,et al.  Management of adult spinal deformity with combined anterior-posterior arthrodesis and Luque-Galveston instrumentation. , 1991, Journal of spinal disorders.

[28]  D. E. Swartz,et al.  Importance of bone mineral density in instrumented spine fusions. , 1991, Spine.

[29]  B. Cunningham,et al.  Triangulation of Pedicular Instrumentation: A Biomechanical Analysis , 1991, Spine.

[30]  B. Fredrickson,et al.  The Syracuse I‐Plate , 1991, Spine.

[31]  O. Boachie-Adjei,et al.  Treatment of adult spinal deformity with fusion to the sacrum using CD instrumentation. , 1991, Journal of spinal disorders.

[32]  C C Glueer,et al.  Appropriate use of bone densitometry. , 1989, Radiology.

[33]  T Hansson,et al.  Mineral content and strength of lumbar vertebrae. A cadaver study. , 1989, Acta orthopaedica Scandinavica.

[34]  B. Allen,et al.  A 1988 PERSPECTIVE ON THE GALVESTON TECHNIQUE OF PELVIC FIXATION , 1988, The Orthopedic clinics of North America.

[35]  Kostuik Jp.  Treatment of scoliosis in the adult thoracolumbar spine with special reference to fusion to the sacrum. , 1988 .

[36]  B. Allen,et al.  The Galveston experience with L-rod instrumentation for adolescent idiopathic scoliosis. , 1988, Clinical orthopaedics and related research.

[37]  D. Bradford.  Adult scoliosis. Current concepts of treatment. , 1988, Clinical orthopaedics and related research.

[38]  J. Kostuik.  Treatment of scoliosis in the adult thoracolumbar spine with special reference to fusion to the sacrum. , 1988, The Orthopedic clinics of North America.

[39]  M. Pope,et al.  Depth of insertion of transpedicular vertebral screws into human vertebrae: effect upon screw-vertebra interface strength. , 1988, Journal of spinal disorders.

[40]  A G Patwardhan,et al.  Analysis of the Morphometric Characteristics of the Thoracic and Lumbar Pedicles , 1987, Spine.

[41]  R. Winter,et al.  Fusion to the Sacrum for Nonparalytic Scoliosis in the Adult , 1986, Spine.

[42]  J. Kostuik,et al.  Techniques of internal fixation for degenerative conditions of the lumbar spine. , 1986, Clinical orthopaedics and related research.

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

[44]  R. Biscup,et al.  Segmental spine plates with pedicle screw fixation. A new internal fixation device for disorders of the lumbar and thoracolumbar spine. , 1986, Clinical orthopaedics and related research.

[45]  R Louis,et al.  Fusion of the lumbar and sacral spine by internal fixation with screw plates. , 1986, Clinical orthopaedics and related research.

[46]  R Roy-Camille,et al.  Internal fixation of the lumbar spine with pedicle screw plating. , 1986, Clinical orthopaedics and related research.

[47]  M. Schendel,et al.  Comparison of lumbosacral fixation devices. , 1986, Clinical orthopaedics and related research.

[48]  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.

[49]  McAfee Pc,et al.  A Biomechanical Analysis of Spinal Instrumentation Systems in Thoracolumbar Fractures: Comparison of Traditional Harrington Distraction Instrumentation with Segmental Spinal Instrumentation , 1985 .

[50]  P. McAfee,et al.  A Biomechanical Analysis of Spinal Instrumentation Systems in Thoracolumbar Fractures: Comparison of Traditional Harrington Distraction Instrumentation with Segmental Spinal Instrumentation , 1985, Spine.

[51]  J. Kostuik,et al.  Spinal Fusions to the Sacrum in Adults with Scoliosis , 1983, Spine.

[52]  J. Kostuik.  Decision Making in Adult Scoliosis , 1979, Spine.

[53]  J. Kostuik,et al.  Scoliosis surgery in adults. , 1973, Clinical orthopaedics and related research.

[54]  J K Weaver,et al.  Cancellous bone: its strength and changes with aging and an evaluation of some methods for measuring its mineral content. , 1966, The Journal of bone and joint surgery. American volume.