Sutterlin Chester E, Field Antony, Ferrara Lisa A, Freeman Andrew L, Phan Kevin
Department of Neurosurgery, University of Florida, Gainesville, Florida, USA;; Spinal Health International, Longboat Key, Florida, USA.
Auckland City Hospital and Starship Children's Hospital, Grafton, Auckland 1023, New Zealand.
J Spine Surg. 2016 Dec;2(4):266-276. doi: 10.21037/jss.2016.11.01.
S1 screw failure and L5/S1 non-union are issues with long fusions to S1. Improved construct stiffness and S1 screw offloading can help avoid this. S2AI screws have shown to provide similar stiffness to iliac screws when added to L3-S1 constructs. We sought to examine and compare the biomechanical effects on an L2-S1 pedicle screw construct of adding S2AI screws, AxiaLIF, L5-S1 interbody support via transforaminal lumbar interbody fusion (TLIF), and to examine the effect of the addition of cross connectors to each of these constructs.
Two S1 screws and one rod with strain gauges (at L5/S1) were used in L2-S1 screw-rod constructs in 7 L1-pelvis specimens (two with low BMD). ROM, S1 screw and rod strain were assessed using a pure-moment flexibility testing protocol. Specimens were tested intact, and then in five instrumentation states consisting of: (I) Pedicle screws (PS) L2-S1; (II) PS + S2AI screws; (III) PS + TLIF L5/S1; (IV) PS + AxiaLIF L5/S1; (V) PS + S2AI + AxiaLIF L5/S1. The five instrumentation conditions were also tested with crosslinks at L2/3 and S1/2. Tests were conducted in flexion-extension, lateral bending and axial torsion with no compressive preload.
S2A1 produces reduced S1 screw strain for flexion-extension, lateral bending and axial torsion, as well as reduced rod strain in lateral bending and axial torsion in comparison to AxiaLIF and interbody instrumentation, at the expense of increased rod flexion-extension strain. Cross-connectors may have a role in further reduction of S1 screw and rod strain.
From a biomechanical standpoint, the use of the S2AI technique is at least equivalent to traditional iliac screws, but offers lower prominence and ease of assembly compared to conventional sacroiliac stabilization.
S1螺钉失效和L5/S1不愈合是与S1进行长节段融合时存在的问题。提高内固定结构刚度和减轻S1螺钉负荷有助于避免这些问题。在L3-S1结构中添加S2AI螺钉后，其刚度与髂骨螺钉相似。我们试图研究并比较添加S2AI螺钉、AxiaLIF、经椎间孔腰椎椎间融合术（TLIF）进行L5-S1椎间支撑对L2-S1椎弓根螺钉结构的生物力学影响，并研究在这些结构中添加横向连接器的效果。
在7个L1-骨盆标本（2个骨密度低）的L2-S1螺钉-棒结构中使用2枚S1螺钉和1根带有应变片（位于L5/S1）的棒。使用纯力矩柔韧性测试方案评估活动度、S1螺钉和棒的应变。对标本进行完整测试，然后在以下五种内固定状态下测试：（I）L2-S1椎弓根螺钉（PS）；（II）PS + S2AI螺钉；（III）PS + L5/S1 TLIF；（IV）PS + L5/S1 AxiaLIF；（V）PS + S2AI + L5/S1 AxiaLIF。这五种内固定情况也在L2/3和S1/2处使用横向连接器进行测试。测试在无压缩预负荷的情况下进行屈伸、侧弯和轴向扭转。
与AxiaLIF和椎间融合内固定相比，S2A1在屈伸、侧弯和轴向扭转时可降低S1螺钉应变，在侧弯和轴向扭转时可降低棒的应变，但代价是增加了棒的屈伸应变。横向连接器可能在进一步降低S1螺钉和棒的应变方面发挥作用。
从生物力学角度来看，S2AI技术的使用至少与传统髂骨螺钉相当，但与传统骶髂关节稳定术相比，其突出程度更低且易于组装。
