マーゲル法におけるX線透視下の安全で的確なスクリュー刺入法について

A Safe and Accurate Method for Inserting C1-C2 Transarticular Screws Under Intraoperative Fluoroscopy

　抄録：マーゲル法施行例で骨形態とスクリュー方向を検討し，X線透視下の安全で的確なスクリュー刺入法を考案した．椎骨動脈損傷例の術後CT像から損傷は環椎でなく軸椎横突孔付近で好発すると考えた．41例の正面と側面の術後X線像でスクリュー通過点を計測し，術後CT像でスクリューが，軸椎横突孔から離れていたかで安全性を，環軸関節中央部を貫通したかで的確性を評価した．X線像計測とCT像評価を対比した結果，亜脱臼整復例では正面像で軸椎上関節面の内側1/4の点～外側1/3の点，同時に側面像で軸椎椎弓起始部上縁レベルの椎体の後方1/5の点～中点を通過すれば，100％の安全性と82％の的確性で刺入できた．整復不能例でも，正面像で軸椎上関節面内縁から43％未満の内側，または側面像で椎体後縁から49％未満の後方を通過すれば100％安全であった．軸椎横突孔の内側偏在と後方偏在の合併や高度亜脱臼の遺残はハイリスク例であった．

　The author investigated the safety and accuracy of a method for inserting C1-C2 transarticular screws under intraoperative fluoroscopy as a means of preventing vertebral artery (VA) injury and allowing fixation of the screw at the center of the C1-C2 joint. A CT scan of an os odontoideum patient with VA injury showed penetration of the C2 transverse foramen (TF) by the drill point. Anatomically, the wall of the C2 TF consists of the pedicle cortex, and the VA runs laterally after emerging from the C2 TF. This makes VA injury at the C2 TF level more likely than at the C1 level if the screw is directed medially. On postoperative A-P and lateral radiographs of 41 patients undergoing screw insertion, the screw trajectories in C2 were measured. On postoperative CT scans, the interval between the screw and the C2 TF was measured to evaluate safety and the point of screw-penetration into the C1-C2 joint was investigated to evaluate accuracy. Comparison of radiographic measurements with CT evaluations revealed that the realigned C1-C2 joint could be screwed with 100％ safety and 82％ accuracy in a trajectory extending from the medial 1/4 point to the lateral 1/3 point of the C2 superior articular process (SAP) surface on A-P radiographs and from the posterior 1/5 point to the midpoint of the C2 vertebral body at the lamina-originating level on lateral radiographs. In cases of irreducible C1 subluxation, 100％ safety could be achieved in a trajectory through the medial part to a point 43％ of the C2 SAP surface from the medial margin on A-P radiographs or through the posterior part to a point 49％ of the C2 vertebral body from the posterior margin on lateral radiographs. In patients with irreducidle high-grade subluxation of C1 or both medial and posterior deviation of the C2 TF, screw insertion was associated with a high rate of VA injury.