STP1431: Vertebral Bone Density—A Critical Element in the Performance of Spinal Implants

    Tan, JS
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Kwon, BK
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Samarasekera, D
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Dvorak, MF
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Fisher, CG
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Oxland, TR
    Student, Orthopaedic Spine Surgeon, Research Assistant, Head of Division of Spinal Surgery, Orthopaedic Spine Surgeon, Head of Division of Orthopaedic Engineering, University of British Columbia, Vancouver, BC

    Pages: 14    Published: Jan 2003


    Abstract

    The effectiveness of spinal implants in fixation is dependent upon the bone-implant interface, and thus on vertebral bone density. Current ASTM assessment methods use synthetic elements as vertebral surrogates and therefore, by definition, do not address important in vivo performance and failure characteristics. The purpose of this study is to contrast the mechanical behaviour of pedicle screws in cadaveric vertebrae versus synthetic surrogates. Short-term physiologic axial compression and bending moment were cyclically applied to pedicle screws inserted in lumbar vertebrae and UHMWPE. Kinematics of the pedicle screws in bone and in UHMWPE were significantly different in terms of the range of motion and pivoting and bending points on the screws. For the vertebral fixation, there was a trend towards a more rigid screw-bone interface with increasing bone mineral density. Devices tested using ASTM and ISO test standards may give clinicians and regulatory bodies a false sense of security with respect to implant performance due to their limited scope.

    Keywords:

    bone mineral density, pedicle screw, mechanical testing, implant loosening


    Paper ID: STP11146S

    Committee/Subcommittee: F04.25

    DOI: 10.1520/STP11146S


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