Zheng Guoyan, Zhang Xuan, Haschtmann Daniel, Gédet Philippe, Langlotz Frank, Nolte Lutz P
MEM Research Center ISTB, University of Bern, Bern, Switzerland.
Comput Aided Surg. 2007 May;12(3):138-51. doi: 10.3109/10929080701388091.
One of the difficult steps in intra-medullary nailing of femoral shaft fractures is distal locking - the insertion of distal interlocking screws. Conventionally, this is performed using repeated image acquisitions, which leads to considerable irradiation of the patient and surgical team. Virtual fluoroscopy has been used to reduce radiation exposure, but can only provide multi-planar two-dimensional projection views. In this study, two calibrated fluoroscopic images were used to automatically recover the positions and orientations of the distal locking holes (DLHs). The ultimate goal is to provide precise three-dimensional guidance during distal locking.
A model-based optimal fitting process was used to reconstruct the positions and orientations of the DLHs from two calibrated fluoroscopic images. No human intervention is required. A preliminary in vitro validation study was conducted to analyze the accuracy and reliability of the technique using images acquired from different viewpoints. The ground truths of the DLH were obtained by inserting a custom-made steel rod through the hole and then digitizing both the top and bottom centers of the rod using a sharp pointer. The recovery errors were computed by comparing the computed results to the ground truths.
In all experiments, the poses of the DLHs could be recovered fully automatically. When the recovered positions and orientations of the DLHs were compared to their associated ground truths, a mean angular error of 0.5 degrees (STD = 0.2 degrees ), and a mean translational error of 0.1 mm (STD = 0.0 mm) were found.
Accurate and reliable pose recovery of distal locking holes from two calibrated fluoroscopic images is achievable. Our preliminary in vitro experimental results demonstrate that the recovered poses of the distal locking holes are sufficiently accurate for intra-operative use.
股骨干骨折髓内钉固定术中的难点之一是远端锁定——插入远端交锁螺钉。传统上，这需要反复进行图像采集，这会使患者和手术团队受到大量辐射。虚拟透视已被用于减少辐射暴露，但只能提供多平面二维投影视图。在本研究中，使用两张校准后的透视图像自动恢复远端锁定孔（DLHs）的位置和方向。最终目标是在远端锁定过程中提供精确的三维引导。
基于模型的最优拟合过程用于从两张校准后的透视图像重建DLHs的位置和方向。无需人工干预。进行了一项初步的体外验证研究，以使用从不同视角获取的图像分析该技术的准确性和可靠性。通过将定制的钢棒插入孔中，然后使用尖锐指针数字化钢棒顶部和底部中心来获得DLH的真实值。通过将计算结果与真实值进行比较来计算恢复误差。
在所有实验中，DLHs的位姿均可完全自动恢复。将DLHs恢复的位置和方向与其相关的真实值进行比较时，发现平均角度误差为0.5度（标准差 = 0.2度），平均平移误差为0.1毫米（标准差 = 0.0毫米）。
从两张校准后的透视图像中准确可靠地恢复远端锁定孔的位姿是可行的。我们初步的体外实验结果表明，恢复的远端锁定孔位姿在术中使用时足够精确。
