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  • Biomechanical evaluation of proximal junctional segments following long-segment pedicle screw-only versus hybrid fixation

    Final Number:

    Vibhu Krishnan Viswanathan; Ranjit Ganguly MD; Amy Minnema; Nicole Watson; Nicole Grosland; Douglas C. Fredericks; Stephanus Viljoen MD; Francis Farhadi MD PhD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2017 Annual Meeting - Late Breaking Science

    Introduction: Proximal junctional failure (PJF) is a serious complication following spinal deformity surgery. The major predisposing biomechanical factor is thought to be the abrupt change in stress between the rigid instrumented and the adjacent mobile segments. Proximal sublaminar band (SLB) placement represents a novel technique that may widen this “transitional zone” and mitigate the risk of PJF. The current study analyzes the biomechanical properties of hybrid constructs in a human cadaveric model.

    Methods: Ten fresh frozen human thoracolumbar spines (T7-L2) underwent flexibility tests (pure moments in flexion, extension, lateral bending and axial rotation) using the MTS 858 Bionix II System. Intradiscal pressure measurements were performed at the rostral adjacent motion segments. Five cycles of testing were performed: Intact (I), T10-L2 pedicle screw-rod fixation (PS), and hybrid constructs with either supplemental upper instrumented vertebra (UIV) + 1 mersilene tape, UIV + 1 sub-laminar bands (SL1) or UIV + 1/UIV + 2 sub-laminar bands (SL2).

    Results: Flexibility analysis revealed that, as compared to PS, SL1 showed reduced flexibility at UIV + 1 under moments in all directions [flexion (p=0.005), extension (p=0.022), right and left lateral bending (p=0.005), and right (p=0.008)/left axial rotation (p=0.005)]. Similarly, as compared to PS, SL2 showed reduced flexibility at UIV + 1 [all directions (p=0.028)] and at UIV+2 [flexion (p=0.046), right lateral bending (p=0.028), and right/left axial rotation (p=0.028)]. SL1 versus PS intra-discal pressure analysis revealed reduced pressure changes at UIV+1 in flexion (p=0.013) and right (p=0.028)/left (p=0.007) axial rotation. SL2 yet further reduced intradiscal pressure changes at both UIV+1 and UIV+2.

    Conclusions: SLB insertion reduced flexibility and intra-discal pressures at the UIV+1 level in our cadaveric model. This observation supports a potential role for SLB in mitigating stress at the proximal junctional levels.

    Patient Care: This cadaveric study provides biomechanical evidence in support of a role for sublaminar bands in reducing stress at the proximal junctional levels. This data could provide further rationale for testing this technology in human clinical trials.

    Learning Objectives: 1. UIV + 1 SLB insertion reduces proximal junctional flexibility 2. UIV + 1 SLB insertion reduces proximal junctional intradiscal pressures 3. SLB insertion allows for semi-rigid fixation and potential transitional zone widening at the proximal junctional levels


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