後側經寰樞椎關節骨釘固定術之電腦輔助路徑規劃及其成效分析

Abstract

簡介：寰樞椎生理結構特殊且活動度大，相較其他節頸椎更容易因外力與疾病導致滑脫進而壓迫神經與脊髓，臨床針對輕微患者透過復位調整、配戴頸圈來治療，嚴重者則需透過復位調整加上內固定手術進行治療。後側經寰樞椎關節固定術是用於治療寰樞椎不穩定患者之手術方法，能提供良好的穩定度，是現今治療寰樞椎不穩定患者之黃金準則。但該手術伴隨高併發症比率，可能導致神經麻痺、癱瘓甚至出血、死亡等情況。故近年來許多學者提倡透過術前規劃或定位巡航以降低術中併發症。 目的：術後實際路徑應符合規劃路徑以達規劃之最大成效，故本研究首先將分析術前規劃路徑與術後實際路徑之一致性，並分析施打路徑之參數間關聯性。此外，術中骨釘之施打將穿越寰樞椎以達固定效果；然而骨釘在施打時，可能對寰樞椎造成關節間緊迫或因植釘時施加之外力被推遠，甚至旋轉與側彎等改變，故本研究也將針對病患術前術後寰樞椎相對位置做分析探討。最後我們將分析不同骨釘施打路徑對於術後寰樞椎之相對運動是否有相關性。 材料與方法：本研究回顧了19位進行後側寰樞椎經關節固定術病患之術前術後影像資訊，病患平均年齡為61.1歲。病患術前先接受寰樞椎位置復位調整，接著拍攝斷層掃描並進行術前路徑規劃，且於術後再次進行斷層掃描拍攝。測量路徑一致性透過規劃路徑與實際路徑的斷層掃描影像進行量測，量測參數包含：進入點、垂直角、水平角、骨釘長度與目標點。在寰樞椎術後位置與角度改變量測則透過軟體分別於寰椎與樞椎上建立參考座標軸，再計算出距離與角度變化。

結果：術前術後結果顯示進入點不論在水平或垂直之差異都未達顯著，水平角及骨釘長度亦有同樣結果，但垂直角術後比起術前有顯著變大，術後目標點相較術前有分布於較接近顱側且較後方區域之趨勢。相關性探討發現進入點與角度具有關聯性，當進入點較接近顱側時垂直角會有變小之現象，而當進入點較外側時水平角會有向心旋轉之改變。在術後寰樞椎位置與角度結果顯示，術後病患寰樞椎相對位置與角度顯示當病患寰樞椎垂直距離改變時，將伴隨前彎後仰之趨勢。另外本研究發現，當術中垂直角與規劃路徑有所差異時，病患寰樞椎距離會具有相對應改變，針對此結果我們認為當骨釘進入角度改變時，會伴隨骨釘施力之水平分量與垂直分量改變，使病患寰樞椎術後相對距離受到影響。 結論：透過電腦輔助路徑規劃系統進行手術，相較以往能有效施打骨釘且降低併發症發生率，透過本研究分析規劃路徑與實際路徑間存在之差異，能提供術前規劃時加入與實際路徑差異之考量，且在手術操作時了解術前規劃路徑輔助與實際路徑存在多大之差異。而實際路徑與規劃路徑之垂直角不同，將影響寰樞椎相對距離，這結果將成為醫師進行後側經寰樞椎關節固定術時施打垂直角之考量。

Objective: To evaluate the feasibility of preoperative computer-assisted trajectory planning for posterior atlantoaxial transarticular screw fixation with surgical outcomes. Introduction: Cervical C1-C2 instability or dislocation, usually caused by trauma or rheumatoid arthritis, results in nerve compression and assorted disorders. Most of patients can be cured by reduction treatment with the use of neck collar. The patients who suffer from severe symptoms may need surgical treatment. Posterior atlantoaxial fixation with transarticular screw (TAS) is a common treatment for atlantoaxial joint instability due to good stabilization efficacy. However, high complication rates were reported. Complications resulted from screw malposition and neurovascular deficit are catastrophic and fatal. Therefore, constructing patient’s individual 3D cervical images and planning TAS trajectory with a computer program prior to surgery are suggested to avoid fetal complications. Ideally, the TAS should penetrate four articular surfaces of C1-C2, and the screw tip should reach anterior surface of C1 arch without crashing the nerve and vertebral artery. The feasibility of preoperative planning of screw trajectory depends on whether the intra-surgical screw pathway follows the planned route or not. In addition, the change of C1-C2 relative position after surgery remains unclear. The purpose of this study is in two-fold. The first one is to evaluate the consistency between the virtually-planned and intra-surgical screw trajectory. The second one is to find the correlations between the parameters of screw insertion and the change of C1-C2 relative position after surgery.

Material and Method: Nineteen patients (average age: 61.1 years; range: 35-71 years) in need of posterior atlantoaxial transarticular fixation based on diagnosis of experienced neurosurgeons were recruited. Prior to surgery, all patients underwent computer tomography (CT) scan for screw trajectory planning. A trajectory planning computer program was self-designed to reconstruct a patient’s 3D cervical images with functions of multi-planar section display. The program allowed the evaluation of surface anatomy of cervical spine, which helped surgeons to determine the screw entry point, the horizontal and vertical insertion angle, and the screw size. The patients underwent another CT scan at follow up examination. The following parameters were measured to analyze the deviations between the virtually-planned and intra-surgical screw trajectory: entry point, vertical angle, horizontal angle, and screw length and target point. The pre and post-operative position of C1 and C2 were measured. Result: (a). Surgical outcome. Overall, 32 transarticular screws were inserted. No massive bleeding and major complications were found. (b). Deviation of screw trajectory. The vertical angle of intra-surgical screw insertion was significantly larger than that of virtually-planned one (p<0.05). Other parameters of screw insertion were similar between the virtually-planned and the intra-surgical screw trajectory. (c). Correlation between parameters. Moderate negative correlation was found between vertical entry point and vertical angle (R=0.567, p=0.01), and moderate positive correlation was found between horizontal entry point and horizontal angle (R=0.378, p=0.039). The increase of intraoperative vertical angle decreased the distance between C1 and C2 along X-axis direction but increased the distance along Y-axis direction.

Conclusion: This study indicates that surgeon can learn the individual stereotactic characteristics of patient’s cervical structures during preoperative screw trajectory planning, and thus insert screw more precisely without injuring soft tissue duirng surgery. This study also indicates that higher vertical angle of screw insertion will shorten the distance of C1-C2 after fixation, which may release the pain and the nerve compression resulted from C1-C2 dislocation.