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  • Biomechanics of the Spire-Z System

    Final Number:

    Jakub Godzik MD; Samuel Kalb MD; Eduardo Martinez del Campo MD; Corey Tyler Walker MD, BS; Anna Newcomb; Steve W. Chang MD; Neil R. Crawford PhD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2015 Annual Meeting

    Introduction: Interspinous devices stabilize the lumbar spine to promote interbody fusion. In this study, authors evaluate the biomechanics of lumbar motion segments instrumented with the CD HORIZON Spire Z plate system (SpireZ) as a stand-alone device and in the presence of secondary fixation.

    Methods: Standard nondestructive flexibility tests were performed in seven L2-5 human cadaveric spines. Spinal stability determined as mean range of motion (ROM) in flexion/extension, lateral bending, and axial rotation. Paired comparisons were between the following conditions: 1) intact/control; 2) SpireZ device alone; 3) SpireZ with unilateral pedicle screw/rod system (UPSR); 3) SpireZ with unilateral facet screw system (UFS); 4) SpireZ with bilateral facet screw system (BFS). Stiffness and range of motion (ROM) data were compared using one-way analysis of variance.

    Results: SpireZ was most effective in limiting flexion (80% of normal) and extension (76% of normal), while less effective in reducing lateral bending and axial rotation. In lateral bending, the SpireZ+BFS and SpireZ+UPSR constructs were equivalent and demonstrated greater ROM reduction compared to SpireZ+UFS and SpireZ standalone. SpireZ+BFS demonstrated greatest stiffness in axial rotation in comparison to SpireZ+UPSR (p=0.025), SpireZ+UFS (p=0.001), and SpireZ standalone (p<0.001). SpireZ+UPSR was equivalent to SpireZ+UFS (p=0.21) and superior to SpireZ standalone (p=0.013).

    Conclusions: The SpireZ device provides excellent immediate fixation, particularly for flexion and extension. While the hybrid SpireZ and bilateral facet screw construct afforded the greatest stability, SpireZ with UPS demonstrated considerable promise.

    Patient Care: The interspinous device SpireZ may represent an alternative option for lumbar fusion, particularly as a component of a hybrid system with facet or pedicle screws. However, given the biomechanical nature of the study it is difficult to extrapolate the clinical ramifications of this study.

    Learning Objectives: By the end of this session, the participants should be able to (1) describe what the interspinous device SpireZ is, (2) describe the stability of the SpireZ standalone device in a cadaveric model, (3) understand the relative stability of the SpireZ with three differing systems.


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