Optimizing Biomechanics of Surgical Correction for Lumbar Flatback Deformity

目的：本研究的长期目标是改善腰椎间盘突出症的手术治疗效果。 平背畸形，这是一种复杂的疾病，可以影响很大一部分退伍军人。在 平背畸形躯干前倾，影响患者直立和行走的能力， 肌肉疲劳和背痛加剧，导致功能丧失。手术的目的是矫正矢状面 对线不良，以减少肌肉疲劳，并允许患者直立行走，从而改善 功能治疗老年退伍军人的外科医生想知道：（1）脊柱前凸恢复多少足以 减少肌肉负担，以保持直立姿势;（2）这是否可以通过使用侵入性较小的 手术技术，以尽量减少并发症和发病率。 假设：我们的中心假设是使用脊柱前凸椎间融合器恢复腰椎前凸 植入多个椎间盘间隙将最大限度地减少保持标本直立姿势所需的力 L4至骶骨脊柱前凸消失 具体目的：（1）我们将使用人类尸体胸腰椎（T10-骶骨）脊柱标本， PI值（35 °-70 °;成人平均PI为52 °），用于量化头侧所需的剪切力和力矩 和尾侧边界的标本，以保持直立的站立姿势在以下条件： (1)L4-S1椎体前凸降低，导致PI-LL不匹配（退行性或医源性），和（2）改善 L1-S1脊柱前凸，首先在腰椎的一个或多个节段放置前凸椎间融合器 不进行后柱（关节面）截骨术（PCO）。 (2)我们将分析目标1中收集的数据，以：（1）定义PI-LL不匹配程度之间的关系， 以及为重建的脊柱保持直立站立姿势所需的力，以及（2）量化 以下研究变量对脊柱前凸椎间融合器改善站立腰椎功能的影响 脊柱前凸：（a）重建椎间隙的数量，（B）标本的PI值和柔韧性（即节段性 屈曲和伸展中的移动性），（c）PCO对产生额外矫正的影响。 方法：实验设计包括两组：退行性和医源性。在医源性手臂中， 通过对插入的椎弓根螺钉施加牵引力，实现L4-S1的低脊柱融合 L4、L5和S1椎弓根;然而，在退行性组中，我们将选择有足够丢失的标本 L5-S1和L4-L5椎间隙的椎间盘高度。在医源性组中，L1-S1脊柱前凸的手术恢复 将通过在L3-L4和L2-L3椎间隙头侧植入脊柱前凸椎间融合器进行 L4-S1脊柱前凸下融合;而在退行性臂中，节段性脊柱前凸的手术恢复将 在L5-S1和L4-L5椎间盘间隙进行。在两组研究中，我们的目标是消除PI-LL不匹配 （PI-LL ≤ 5 °），在植入脊柱前凸椎间融合器的位置增加额外节段，如有必要， 进行后柱（关节面）截骨术，以增强椎间融合器的矫正潜力。在每个 声明样本将接受一系列生物力学测试，以量化剪切力和力矩 需要在标本的头部和尾部边界保持直立姿势。 统计分析将包括重复测量ANOVA和多变量回归分析。 临床影响：预计受平背畸形影响的在世退伍军人的总体百分比为 预计随着人口老龄化和寿命延长，因此，建议的研究对 照顾我们退伍军人的VA提供者的知识可能很重要。如果生物力学数据支持 使用椎间融合器进行节段性脊柱前凸恢复，微创技术将增加 恢复老年患者腰椎前凸的有价值的选择。研究结果适用于 如果发现对退伍军人和平民患者有益，则快速翻译。

Purpose: The long-term goal of this research is to improve the outcomes of surgical correction for lumbar flatback deformity, which is a complex disorder that can affect a large segment of the veteran population. In flatback deformity the torso pitches forward and affects the patient’s ability to stand upright and walk due to muscle fatigue and worsening back pain, leading to functional loss. The goal of surgery is to correct the sagittal malalignment to reduce muscle fatigue and allow patients to stand upright and ambulate, thus improving function. Surgeons who treat older veterans want to know: (1) how much lordosis restoration is sufficient to reduce the burden on muscles to maintain an upright posture; and (2) can this be achieved using a less invasive surgical technique to minimize complications and morbidity. Hypothesis: Our central hypothesis is that restoring lumbar lordosis using lordotic interbody fusion cages implanted in multiple disc spaces will minimize the forces needed to maintain an upright posture in specimens with loss of lordosis across L4 to sacrum. Specific aims: (1) We will use human cadaveric thoracolumbar (T10-sacrum) spine specimens with a range of PI values (35°-70°; the average adult PI is 52°) to quantify the shear force and moment required at the cephalad and caudal boundaries of the specimen to maintain an upright standing posture under the following conditions: (1) hypolordosis across L4-S1, creating a PI-LL mismatch (degenerative or iatrogenic), and (2) improvement of L1-S1 lordosis using lordotic interbody fusion cages placed at one or more segments of the lumbar spine, first without and then with posterior column (facet) osteotomies (PCO). (2) We will analyze the data collected in aim 1 to: (1) define a relationship between the extent of PI-LL mismatch and forces needed to maintain an upright standing posture for the reconstructed spines, and (2) quantify the influence of the following study variables on the ability of lordotic interbody cages to improve standing lumbar lordosis: (a) number of reconstructed disc spaces, (b) specimen’s PI value and flexibility (that is, segmental mobility in flexion and extension), (c) influence of PCO to yield additional correction. Methods: The experimental design consists of two arms: degenerative, and iatrogenic. In the iatrogenic arm, a hypolordotic fusion across L4-S1 will be created by applying distraction forces across pedicle screws inserted in L4, L5 and S1 pedicles; whereas, in the degenerative arm we will select specimens in which there is sufficient loss of disc heights at the L5-S1 and L4-L5 disc spaces. In the iatrogenic arm, surgical restoration of L1-S1 lordosis will be performed by implanting lordotic interbody cages at L3-L4 and L2-L3 disc spaces cephalad to the hypolordotic L4-S1 fusion; whereas, in the degenerative arm surgical restoration of segmental lordosis will be performed at L5-S1 and L4-L5 disc spaces. In both arms of the study, we will aim to eliminate the PI-LL mismatch (PI-LL ≤5°) by adding additional segments where lordotic interbody cages are implanted and, if necessary, performing posterior column (facet) osteotomies to augment the correction potential of interbody cages. In each state the specimens will undergo a battery of biomechanical tests to quantify the shear force and moment required at the cephalad and caudal boundaries of the specimen to maintain an upright posture. Statistical analysis will include repeated-measures ANOVA and multivariate regression analyses. Clinical Impact: The overall percentage of living Veterans expected to be affected by flatback deformity is anticipated to rise as the population ages and lives longer. Thus, the contribution of the proposed research to the knowledge of VA providers who care for our Veterans is likely significant. If the biomechanical data supports the use of segmental lordosis restoration using interbody fusion cages, the less invasive technique will add a valuable option for restoring lumbar lordosis in older patients. The research results are readily applicable for quick translation to veteran- and civilian patients if found to be beneficial.