FREE-HAND PLACEMENT OF C7 PEDICLE SCREWS: A CADAVERIC STUDY

Objective : To evaluate the accuracy of free-hand pedicle screws placement at the seventh cervical vertebra. Methods : The authors have exposed the cervicothoracic junction of 9 adult cadavers (7 male and 2 female) preserved in formalin from the Faculty of Medicine of the Universidad Andina Néstor Cáceres Velásquez, city of Juliaca, Puno - Peru, locating the C7 vertebra based on anatomical parameters. According to previous publications, the entry point for the C7 pedicle was determined as 3-4mm lateral and 5-6mm superior to the center of the lateral mass, and the pedicle was drilled manually and instrumented with 3.5mm screws. After the screws placement, the C7 vertebrae were removed for radiographic analysis. Results : The authors were able to adequately locate the C7 entry point in 12 pedicles (66.6% accuracy), finding a great variability both laterally (2-5mm) and cranially (3-10mm). The angulation in the coronal plane was correct in 13 pedicles (72.3%), despite the incorrect location of the entry point. Angle values in the coronal plane ranged from 38 to 62 degrees. In the sagittal plane angulation, 2 screws were placed in the C6-C7 disc. The midtransversal diameter of the 18 pedicles ranged from 4 to 7mm. Conclusions : The location of the entry point for placement of C7 pedicle screws with pure free-hand technique is very variable due to anatomical differences and the authors recommend some type of guidance for increased safety and accuracy.

研究目的：评估徒手置入第七颈椎（C7）椎弓根螺钉的准确性。
研究方法：本研究纳入秘鲁普诺省胡利亚卡市内斯托尔·卡塞雷斯·贝拉斯克斯安第纳大学医学院保存的9具成人福尔马林固定尸体（7具男性、2具女性），通过解剖学参数定位第七颈椎（C7）并暴露颈胸交界处。参照既往研究文献，将C7椎弓根进针点定为侧块中心外侧3~4mm、头侧5~6mm处，随后徒手钻孔并置入3.5mm直径螺钉。螺钉置入完成后，取下C7椎体进行影像学分析。
研究结果：本研究中，12个椎弓根（准确率66.6%）的C7进针点定位准确，同时观察到进针点在外侧方向（偏移2~5mm）及头侧方向（偏移3~10mm）均存在较大变异。尽管部分椎弓根进针点定位不准，但仍有13个椎弓根（72.3%）的冠状面置入角度准确；冠状面角度取值范围为38°~62°。矢状面角度方面，有2枚螺钉置入至C6-C7椎间盘内。18个椎弓根的横径值介于4~7mm之间。
研究结论：由于解剖学个体差异，采用纯徒手技术置入C7椎弓根螺钉的进针点定位存在较大变异；因此本研究作者建议借助辅助导航手段，以提升螺钉置入的安全性与准确性。