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Anterior vertebral body screw pullout testing. A comparison of Zeilke, Kaneda, Universal Spine System, and Universal Spine System with pullout-resistant nut. 1998

I H Lieberman, and R Khazim, and T Woodside
Division of Orthopaedics, Cleveland Clinic Foundation, Ohio, USA.

METHODS A biomechanical study of pullout of anteriorly implanted screws in cadaveric vertebral bodies. OBJECTIVE To investigate and compare the pullout strength of the Zielke, Kaneda, Universal Spine System (USS) pedicle screw, and USS pedicle screw with a new pullout-resistant nut. BACKGROUND A common problem with anterior purchase regardless of the implant system is screw pullout at the proximal and distal ends of multilevel constructs. There is limited information on a solution to this problem. METHODS The L1 to L4 vertebral bodies from four cadavers had one each of Zielke and Kaneda pedicle screws (Acromed Corp., Cleveland, OH), USS pedicle screw (Synthes Spine, Paoli, PA), and USS pedicle screw with pullout-resistant nut implanted transversely across the center of the vertebral body with bicortical purchase in a similar fashion as would be used clinically. The screws were extracted using a servohydraulic material testing system. The maximum axial forces were recorded. RESULTS The Zielke and Kaneda screws had no significant difference in mean pullout strength (P = 0.542). The USS screw alone was less strong (P = 0.009). The USS screw and pullout-resistant nut increased the pullout strength by twofold (P = 0.00006). In the screw pullout tests, the mode of failure was at the screw thread's interface. The USS screw and pullout-resistant nut failed by imploding the body around the nut. With the USS screw and pullout-resistant nut, the pullout strength was determined by the compressive strength of the bone. CONCLUSIONS The addition of a pullout-resistant nut to an anterior vertebral body screw improves the pullout strength by twofold and changes the mode of failure to rely ultimately on the inherent vertebral body strength rather than the screw's characteristics. The addition of a pullout-resistant nut may be applicable to multilevel implant constructs to prevent screw pullout at the top and bottom.

UI MeSH Term Description Entries
D008159 Lumbar Vertebrae VERTEBRAE in the region of the lower BACK below the THORACIC VERTEBRAE and above the SACRAL VERTEBRAE. Vertebrae, Lumbar
D008422 Materials Testing The testing of materials and devices, especially those used for PROSTHESES AND IMPLANTS; SUTURES; TISSUE ADHESIVES; etc., for hardness, strength, durability, safety, efficacy, and biocompatibility. Biocompatibility Testing,Biocompatible Materials Testing,Hemocompatibility Testing,Testing, Biocompatible Materials,Testing, Hemocompatible Materials,Hemocompatibility Testings,Hemocompatible Materials Testing,Materials Testing, Biocompatible,Materials Testing, Hemocompatible,Testing, Biocompatibility,Testing, Hemocompatibility,Testing, Materials,Testings, Biocompatibility
D001863 Bone Screws Specialized devices used in ORTHOPEDIC SURGERY to repair bone fractures. Bone Screw,Screw, Bone,Screws, Bone
D002102 Cadaver A dead body, usually a human body. Corpse,Cadavers,Corpses
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001696 Biomechanical Phenomena The properties, processes, and behavior of biological systems under the action of mechanical forces. Biomechanics,Kinematics,Biomechanic Phenomena,Mechanobiological Phenomena,Biomechanic,Biomechanic Phenomenas,Phenomena, Biomechanic,Phenomena, Biomechanical,Phenomena, Mechanobiological,Phenomenas, Biomechanic
D013123 Spinal Fusion Operative immobilization or ankylosis of two or more vertebrae by fusion of the vertebral bodies with a short bone graft or often with diskectomy or laminectomy. (From Blauvelt & Nelson, A Manual of Orthopaedic Terminology, 5th ed, p236; Dorland, 28th ed) Spondylodesis,Spondylosyndesis,Fusion, Spinal,Fusions, Spinal,Spinal Fusions,Spondylodeses,Spondylosyndeses
D013718 Tensile Strength The maximum stress a material subjected to a stretching load can withstand without tearing. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed, p2001) Strength, Tensile,Strengths, Tensile,Tensile Strengths
D016268 Internal Fixators Internal devices used in osteosynthesis to hold the position of the fracture in proper alignment. By applying the principles of biomedical engineering, the surgeon uses metal plates, nails, rods, etc., for the correction of skeletal defects. Fixation Devices, Internal,Device, Internal Fixation,Devices, Internal Fixation,Fixation Device, Internal,Fixator, Internal,Fixators, Internal,Internal Fixation Device,Internal Fixation Devices,Internal Fixator
D019544 Equipment Failure Analysis The evaluation of incidents involving the loss of function of a device. These evaluations are used for a variety of purposes such as to determine the failure rates, the causes of failures, costs of failures, and the reliability and maintainability of devices. Materials Failure Analysis,Prosthesis Failure Analysis,Analysis, Equipment Failure,Analysis, Materials Failure,Analysis, Prosthesis Failure,Analyses, Equipment Failure,Analyses, Materials Failure,Analyses, Prosthesis Failure,Equipment Failure Analyses,Failure Analyses, Equipment,Failure Analyses, Materials,Failure Analyses, Prosthesis,Failure Analysis, Equipment,Failure Analysis, Materials,Failure Analysis, Prosthesis,Materials Failure Analyses,Prosthesis Failure Analyses

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