Nibu K, Panjabi M M, Oxland T, Cholewicki J
Department of Orthopaedics & Rehabilitation, Yale University, School of Medicine, New Haven, Connecticut 06510, USA.
J Spinal Disord. 1997 Aug;10(4):357-62.
Improvement in laparoscopic surgery requires spinal-fusion devices appropriately designed for this technique. The BAK interbody fusion device (Spine Tech Inc., Minneapolis, MN, U.S.A.), which consists of two titanium screw cages, meets this requirement. Multidirectional stabilizing potential of this device was investigated by using an in vitro human cadaveric model. Four fresh-frozen human lumbosacral spine specimens (L5-S1) were used. The flexibility test consisted of applying six pure moments (flexion, extension, bilateral axial torques, and lateral bending moments) and measuring the ensuing three-dimensional motion. Moments were applied in four load steps: 0, 2.5, 5.0, 7.5, and 10.0 Nm, and for three load and unload cycles. Motion of the top vertebra was recorded during the third load cycle by using a three-dimensional optoelectronic motion-measurement system. The motion parameters studied were the ranges of motion (ROM) and the neutral zone (NZ). Comparing the ROM of the intact specimen and after the fixation, all motions except extension were reduced significantly (p < 0.005). Average percentage decrease in ROM were 45.8% in flexion, 40.4% in axial rotation, and 65.6% in lateral bending. The only significant changes in NZ were a 255.7% increase in extension, a 90.9% increase in axial rotation, and a 70.8% decrease in lateral bending. This biomechanical study revealed that the BAK system provided decreases in ROM in all directions except in extension. The increased NZ in extension and axial rotation is most likely related to the positioning of the implant. Because these implants were placed from the anterior, damage to anterior annulus and anterior longitudinal ligament is inevitable. For clinical relevance, the patients undergoing this surgical procedure should avoid extension motions.
腹腔镜手术的改进需要专门为该技术设计的脊柱融合装置。由两个钛制螺钉融合器组成的BAK椎间融合装置（美国明尼阿波利斯市的Spine Tech公司）满足了这一要求。使用体外人体尸体模型研究了该装置的多向稳定潜力。使用了四个新鲜冷冻的人腰骶椎标本（L5-S1）。灵活性测试包括施加六个纯力矩（前屈、后伸、双侧轴向扭矩和侧弯力矩）并测量随之产生的三维运动。在四个载荷步骤中施加力矩：0、2.5、5.0、7.5和10.0 Nm，并进行三个加载和卸载循环。在第三个加载循环期间，使用三维光电运动测量系统记录上位椎体的运动。研究的运动参数是运动范围（ROM）和中性区（NZ）。比较完整标本和固定后的ROM，除后伸外的所有运动均显著减少（p < 0.005）。ROM的平均百分比下降在前屈中为45.8%，在轴向旋转中为40.4%，在侧弯中为65.6%。NZ的唯一显著变化是后伸增加255.7%，轴向旋转增加90.9%，侧弯减少70.8%。这项生物力学研究表明，BAK系统除后伸外，在所有方向上均减少了ROM。后伸和轴向旋转中NZ的增加很可能与植入物的位置有关。由于这些植入物是从前侧放置的，对前侧纤维环和前纵韧带的损伤是不可避免的。就临床相关性而言，接受该手术的患者应避免后伸运动。
