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  • Multi-Level Kinematic Assessment of Immediate and Simulated Long-Term Stabilization of Novel Inline Cervical Interbody Devices with Intervertebral Screw, Anchor, or Blade Fixation

    Final Number:

    Ivan Cheng; Paul M. Arnold MD; Jonathan A Harris MS; Mir Hussain BS; Brian Karamian MD; Chengmin Zhang PhD; Brandon Bucklen PhD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2017 Annual Meeting

    Introduction: Anterior cervical discectomy and fusion (ACDF) remains the gold standard for cervical spondylotic myelopathy. Multi-level stand-alone ACDF with screw fixation is widely used to reduce tissue retraction associated with anterior plating. However, the relatively aggressive screw trajectory dictates size of the incision. Alternatively, novel intervertebral anchors or bladed devices have been introduced, providing fixation in-line with the operative disc via a curvilinear trajectory to minimize the surgical corridor. Nevertheless, the immediate and long-term biomechanical efficacy of these fixation techniques are unknown.

    Methods: Fifteen cadaveric lumbar specimens (C2-C7) were divided in three groups: (a) traditional intervertebral body screws (MIS-S), (b) novel anchor (MIS-A) fixation, and (c) blade fixation (MIS-B). Operative constructs (C4-C6) include: 1) intact, 2) integrated stand-alone device (iSA), 3) iS with lateral mass screws (LMS+iS), and 4) iSA following simulated fatigue. Load control (±1.5Nm) testing was performed in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Simulated in vivo fatigue of iSA devices produced maximum FE, LB, and AR motions for 1,000 cycles at 0.5 Hz. Comparisons were made between groups (significance at p<0.05).

    Results: Across all fixation groups (MIS-S, MIS-A, MIS-B), motion trends in all planes followed: LMS+S < iSA < Intact. iSA reduced intact motion in FE (47%, 67%, and 60%, respectively), LB (43%, 65%, and 57%), and AR (43%, 65%, and 57%) (Fig. 1). LMS reduced motion in all planes to 90-95%. Simulated in vivo fatigue significantly increased motion (Fig. 1) of all treatment groups (all p<0.05). No significant differences in both immediate and long-term fixation were observed in iSA treatment groups, in all planes of motion (p>0.05).

    Conclusions: The present study provided the first biomechanical data of in-line ACDF. Both immediate and long-term stability followed the general trend: anchors > blades > screws; however, both experimental fixation methods provided statistically equivalent fixation compared to intervertebral screws.

    Patient Care: Patient care may be improved by gaining an understanding of the performance of alternative fixation techniques available on market.

    Learning Objectives: To biomechanically quantify immediate stability and fixation following simulated in vivo fatigue of two-level integrated ACDF with anchor or blade intervertebral fixation compared with integrated ACDF with traditional screw fixation.


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