Lange Tobias, Schmoelz Werner, Gosheger Georg, Eichinger Martin, Heinrichs Christian H, Boevingloh Albert Schulze, Schulte Tobias L
Department of Orthopedics and Tumor Orthopedics, Münster University Hospital, Albert-Schweitzer-Campus 1, 48149 Münster, Germany.
Department of Trauma Surgery, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria.
Spine J. 2017 Aug;17(8):1148-1155. doi: 10.1016/j.spinee.2017.03.021. Epub 2017 Mar 31.
Proximal junctional kyphosis (PJK) is a challenging complication after rigid posterior instrumentation (RI) of the spine. Several risk factors have been described in literature so far, including the rigidity of the cranial aspect of the implant.
The aim of this biomechanical study was to compare different proximal implants designed to gradually reduce the stiffness between the instrumented and non-instrumented spine.
STUDY DESIGN/SETTING: This is a biomechanical study.
Eight calf lumbar spines (L2-L6) underwent RI with a titanium pedicle screw rod construct at L4-L6. The proximal transition segment (L3-L4) was instrumented stepwise with different supplementary implants-spinal bands (SB), cerclage wires (CW), hybrid rods (HR), hinged pedicle screws (HPS), or lamina hooks (LH)-and compared with an all-pedicle screw construct (APS). The flexibility of each segment (L2-L6) was tested with pure moments of ±10.0 Nm in the native state and for each implant at L3-L4, and the segmental range of motion (ROM) was evaluated.
On flexion and extension, the native uninstrumented L3-L4 segment showed a mean ROM of 7.3°. The CW reduced the mean ROM to 42.5%, SB to 41.1%, HR to 13.7%, HPS to 12.3%, LH to 6.8%, and APS to 12.3%. On lateral bending, the native segment L3-L4 showed a mean ROM of 15°. The CW reduced the mean ROM to 58.0%, SB to 78.0%, HR to 6.7%, HPS to 6.7%, LH to 10.0%, and APS to 3.3%. On axial rotation, the uninstrumented L3-L4 segment showed a mean ROM of 2.7°. The CW reduced the mean ROM to 55.6%, SB to 77.8%, HR to 55.6%, HPS to 55.6%, LH to 29.6%, and APS to 37.0%.
Using CW or SB at the proximal transition segment of a long RI reduced rigidity by about 60% in relation to flexion and extension in that segment, whereas the other implants tested had a high degree of rigidity comparable with APS. Clinical randomized controlled trials are needed to elucidate whether this strategy might be effective for preventing PJK.
近端交界性后凸（PJK）是脊柱后路坚强内固定术后一种具有挑战性的并发症。目前文献中已描述了多种危险因素，包括植入物头端的刚度。
本生物力学研究旨在比较不同的近端植入物，这些植入物旨在逐步降低内固定节段与未固定节段脊柱之间的刚度。
研究设计/地点：这是一项生物力学研究。
八具小牛腰椎标本（L2-L6）在L4-L6节段采用钛椎弓根螺钉棒系统进行后路内固定。近端过渡节段（L3-L4）逐步采用不同的辅助植入物——脊柱束带（SB）、环扎钢丝（CW）、混合棒（HR）、铰链式椎弓根螺钉（HPS）或椎板钩（LH）——进行固定，并与全椎弓根螺钉结构（APS）进行比较。在自然状态下以及L3-L4节段每种植入物固定后，对每个节段（L2-L6）施加±10.0 Nm的纯力矩来测试其灵活性，并评估节段活动度（ROM）。
在屈伸运动中，未固定的L3-L4自然节段平均ROM为7.3°。环扎钢丝（CW）将平均ROM降低至42.5%，脊柱束带（SB）降至41.1%，混合棒（HR）降至13.7%，铰链式椎弓根螺钉（HPS）降至12.3%，椎板钩（LH）降至6.8%，全椎弓根螺钉结构（APS）降至12.3%。在侧方弯曲时，L3-L4自然节段平均ROM为15°。环扎钢丝（CW）将平均ROM降低至58.0%，脊柱束带（SB）降至78.0%，混合棒（HR）降至6.7%，铰链式椎弓根螺钉（HPS）降至6.7%，椎板钩（LH）降至10.0%，全椎弓根螺钉结构（APS）降至3.3%。在轴向旋转时，未固定的L3-L4节段平均ROM为2.7°。环扎钢丝（CW）将平均ROM降低至55.6%，脊柱束带（SB）降至77.8%，混合棒（HR）降至55.6%，铰链式椎弓根螺钉（HPS）降至55.6%，椎板钩（LH）降至29.6%，全椎弓根螺钉结构（APS）降至37.0%。
在长节段后路内固定的近端过渡节段使用环扎钢丝（CW）或脊柱束带（SB），相对于该节段的屈伸运动，可使刚度降低约60%，而测试的其他植入物具有与全椎弓根螺钉结构（APS）相当的高刚度。需要进行临床随机对照试验以阐明该策略对预防PJK是否有效。
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