Tomlinson Tucker, Chen Jack, Upasani Vidyadhar, Mahar Andrew
Orthopedic Biomechanics Research Center, Department of Orthopedics, Rady Children's Hospital San Diego, San Diego, CA 92123, USA.
Spine (Phila Pa 1976). 2008 Sep 15;33(20):2127-33. doi: 10.1097/BRS.0b013e31817bd8d5.
In vitro biomechanical investigation of lumbosacropelvic spinal instrumentation.
Determine whether unilateral iliac fixation, with or without an L6 to S1 interbody graft, provides equivalent biomechanical stability compared with bilateral iliac fixation.
Recent clinical evidence has shown improved clinical outcomes of unilateral iliac fixation compared with bilateral instrumentation that contradicts biomechanical data supporting bilateral instrumentation, although no specific investigation has compared unilateral versus bilateral instrumentation.
Sixteen porcine spines were instrumented with bilateral segmental pedicle screws from L1 to S1 and 5.5-mm titanium rods. Spines were randomized to either have an intact L6 to S1 disc space (n = 8/group) or a full discectomy and intervertebral cage at L6 to S1 (n = 8/group). Four reflective noncolinear markers were attached to both L6 and S1. Spines were tested with bilateral ilium, unilateral ilium, and sacrum-only fixation in flexion, extension, lateral bending, and axial torsion between +/-7.0 Nm. L6 to S1 range of motion (degrees) and mechanical stiffness (Nmm/degrees) were compared between groups with a 2-way analysis of variance (P < 0.05).
No significant differences were found in construct stiffness or L6 to S1 motion between unilateral or bilateral fixation for any test direction and both demonstrated significantly less L6 to S1 motion compared with sacrum-only fixation for all tests (all P values <0.005). Bilateral fixation was significantly stiffer than sacrum-only fixation in flexion and extension (P < 0.0001). The interbody cage significantly decreased construct stiffness in extension, lateral bending, and axial torsion (P < 0.002), and significantly increased L6 to S1 motion in torsion compared with an intact disc (P < 0.03).
There were no biomechanical differences between bilateral and unilateral iliac screw fixation. Intervertebral cage with full discectomy was significantly less stiff than intact. This study provides biomechanical data to correlate with improved clinical outcomes using unilateral iliac screw fixation, and evidence contraindicating full discectomy with intervertebral cage placement.
腰骶骨盆脊柱内固定的体外生物力学研究。
确定单侧髂骨固定（有无L6至S1椎间融合器）与双侧髂骨固定相比是否能提供同等的生物力学稳定性。
近期临床证据显示，与双侧内固定相比，单侧髂骨固定的临床效果有所改善，这与支持双侧内固定的生物力学数据相矛盾，不过尚无具体研究比较单侧与双侧内固定。
16个猪脊柱用从L1至S1的双侧节段性椎弓根螺钉和5.5毫米钛棒进行内固定。脊柱随机分为两组，一组L6至S1椎间盘间隙完整（每组n = 8），另一组L6至S1行全椎间盘切除术并植入椎间融合器（每组n = 8）。在L6和S1上均附着四个反光非共线标记物。脊柱分别采用双侧髂骨、单侧髂骨和仅骶骨固定进行测试，测试范围为+/-7.0牛米的前屈、后伸、侧弯和轴向扭转。采用双向方差分析比较组间L6至S1的活动度（度）和机械刚度（牛毫米/度）（P < 0.05）。
在任何测试方向上，单侧或双侧固定在结构刚度或L6至S1活动度方面均未发现显著差异，且与仅骶骨固定相比，二者在所有测试中L6至S1活动度均显著更小（所有P值<0.005）。双侧固定在屈曲和后伸时比仅骶骨固定显著更硬（P < 0.0001）。与完整椎间盘相比，椎间融合器显著降低了后伸、侧弯和轴向扭转时的结构刚度（P < 0.002），并显著增加了扭转时L6至S1的活动度（P < 0.03）。
双侧和单侧髂骨螺钉固定之间不存在生物力学差异。全椎间盘切除并植入椎间融合器后的刚度明显低于完整椎间盘。本研究提供了生物力学数据，以关联使用单侧髂骨螺钉固定改善的临床结果，并提供了反对全椎间盘切除并植入椎间融合器的证据。
