Department of Anesthesiology, Keck School of Medicine, University of Southern California Health Sciences Center, Los Angeles, CA 90033, USA.
Spine J. 2010 May;10(5):422-32. doi: 10.1016/j.spinee.2010.02.008. Epub 2010 Mar 27.
In pedicle screw fixation surgery, rigid instruments are inserted into a vertebral body. When the instruments are misdirected within the pedicle or advanced too far beyond it, perforations of the inner or outer cortex can cause damage to the spinal nerve roots and spinal cord. These complications can occur despite the use of imaging modalities, such as radiographs, fluoroscopy, and computerized axial tomography (CAT) scans. A-Mode ultrasound (US), a nonionizing modality, merits study for its possible use in such a type of surgery.
The purpose of the study was to determine the utility of A-mode US during pedicle screw placement, to characterize the approach to the marrow-cortex interface, and to obtain the signature profiles of cortex perforations.
A-Mode data were generated on insertion of a forward-viewing transducer (FVT) and a side-viewing transducer (SVT) to successively greater drilled depths along the insertion pathway. A-Mode broadband US backscatter (BUB) pedicle screw emulation experiments were conducted with transducers inserted into drilled sheep vertebral bodies. BUB amplitude patterns were observed and analyzed. Descriptive statistics were used.
In vitro acoustic experiments on vertebral bodies in a water bath were performed with two 1-MHz unfocused transducers to measure sound speed, broadband US attenuation, and backscatter coefficients. Micro-CAT scan three-dimensional (3-D) images of 10 disarticulated vertebral bodies were obtained pre- and postdrilling done in 5-mm depth increments with a flat-bottom drill. BUB patterns were noted of transducers inserted through rostral outer cortex, through the pedicle, and advanced to the ventral marrow-cortex interface. 2.5-MHz FVT and SVT were co-advanced in successive 5-mm increments along the insertion pathway, with BUBs measured at each point and the echoes composited into a single figure. Deliberate perforations of ventral cortex were made.
Evident patterns or measures indicating the proximity of the ventral marrow-cortex interface were: 1) marrow BUB values increasing in amplitude over three distal peaks in most FVT cases (7 out of 10) and SVT cases (9 out of 10); 2) BUB ratio of marrow-cortex interface to the smallest marrow value greater than 2, in all FVT cases (10 out of 10) with FVT mean of 4.00+/-1.82 (2.25-8.33); and 3) a ratio of distal BUB value to starting cortex BUB in the 0. 82 to 1.62 range (mean, 0.98+/-0.30) in 80% of FVT cases. Ventral FVT perforations resulted in a major drop in the BUB value.
The increase in the BUB amplitudes in the distal insertion pathway suggests that, at least with a 2.5-MHz transducer, an approximate 1.5-cm US window exists in most cases, by which close approach of the ventral marrow-cortex interface could be anticipated. Other ratios may serve as stop criteria to prevent further drilling. A precipitous drop in BUB amplitude may be an indication of a cortex perforation.
在经皮椎弓根螺钉固定术中，将刚性器械插入椎体。当器械在椎弓根内或超出椎弓根太远时发生偏离，内或外皮质的穿孔会导致脊神经根和脊髓损伤。尽管使用了影像学方法，如 X 线片、透视和计算机轴向断层扫描 (CAT) 扫描，但这些并发症仍可能发生。A 型超声 (US) 是一种非电离模态，因其在这种类型手术中的潜在用途而值得研究。
本研究旨在确定 A 型 US 在椎弓根螺钉放置过程中的实用性，描述进入骨髓-皮质界面的方法，并获得皮质穿孔的特征性声谱图。
使用正向观察换能器 (FVT) 和侧视换能器 (SVT)，在插入路径上逐次增加更大的钻入深度，生成 A 型数据。使用插入钻入羊椎体的换能器进行 A 型宽带 US 背散射 (BUB) 椎弓根螺钉仿真实验。观察和分析 BUB 幅度模式。使用描述性统计。
在装有两个 1MHz 非聚焦换能器的水槽中的离体椎体上进行声学实验，以测量声速、宽带 US 衰减和背散射系数。使用平头钻以 5mm 的增量深度对 10 个分离的椎体进行预钻孔和后钻孔，获得微 CAT 扫描三维 (3-D) 图像。FVT 和 SVT 以 2.5MHz 的频率共同沿插入路径以连续 5mm 的增量推进，在每个点测量 BUB 并将回波组合成一个单一的图像。故意在腹侧皮质穿孔。
表明接近腹侧骨髓-皮质界面的明显模式或指标为：1) 在大多数 FVT 病例 (7/10) 和 SVT 病例 (9/10) 中，骨髓 BUB 值在三个远端峰值上逐渐增大；2) 骨髓-皮质界面与最小骨髓值的 BUB 比值大于 2，在所有 FVT 病例中 (10/10)，FVT 的平均值为 4.00+/-1.82 (2.25-8.33)；3) 在 80%的 FVT 病例中，远端 BUB 值与起始皮质 BUB 值的比值在 0.82 至 1.62 范围内 (平均值为 0.98+/-0.30)。腹侧 FVT 穿孔导致 BUB 值大幅下降。
在远端插入路径中 BUB 幅度的增加表明，至少在使用 2.5MHz 换能器的情况下，在大多数情况下存在大约 1.5cm 的 US 窗口，可以预计接近腹侧骨髓-皮质界面。其他比值可以作为防止进一步钻孔的停止标准。BUB 幅度的急剧下降可能表明发生了皮质穿孔。
