STP1431: Gauge Length and Mobility of Test Blocks Strongly Affect the Strength and Stiffness of Posterior Occipito-Cervico-Thoracic Corpectomy Constructs

    Slivka, MA
    Research Engineer, DePuy AcroMed, Raynham, MA

    Serhan, H
    Manager of Research and Technology, DePuy AcroMed, Raynham, MA

    Selvitelli, DM
    Product Development Engineer, Mitek Products, Norwood, MA

    Torres, K
    Research Engineer, DePuy AcroMed, Raynham, MA

    Pages: 7    Published: Jan 2003


    Abstract

    This study was conducted to investigate the effect of test block mobility and gauge length on the strength and stiffness of rod-based posterior occipito-cervical-thoracic corpectomy constructs. The influence of inferior test block mobility was studied by evaluating both pivoting and clamped boundary conditions. Gauge length was varied from 55 mm, the shortest possible length, to 196 mm, simulating the connection of the occipital plate down to T3. Static compression bending and torsion tests were performed in general accordance with ASTM Test Methods for Static and Fatigue for Spinal Implant Constructs in a Corpectomy Model (F 1717-96) to determine the strength and stiffness of the various configurations. Additionally, dynamic compression bending tests were performed to determine the fatigue strength of two types of constructs: 1) 76 mm gauge length with pivoting inferior (and superior) blocks, and 2) longest 196 mm gauge length with clamped inferior block (superior block pivoting). As expected, the stiffness and 2% offset yield load of the constructs in static compression bending decreased with increasing gauge length and clamping the inferior test block caused a dramatic increase in both. The torsional stiffness increased when the gauge length was increased from 55 mm to 116 mm due to the addition of cross-connectors, but then decreased with gauge lengths higher than 116 mm despite adding more cross-connectors. Without adding cross-connectors, the stiffness decreased with increasing gauge length. In dynamic compression bending, the endurance limit nearly doubled for the construct with almost three times longer gauge length simply due to clamping the inferior test block.

    Keywords:

    corpectomy, posterior cervical, biomechanical testing model, fatigue


    Paper ID: STP11127S

    Committee/Subcommittee: F04.25

    DOI: 10.1520/STP11127S


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