椎体CT值在预测颈椎前路融合术后早期内置物沉降中的应用价值

Application of cervical CT value in predicting early implant subsidence after anterior cervical fusion surgery

目的:研究颈椎椎体CT值在预测颈椎前路融合术后早期内置物沉降中的应用价值。方法:回顾性分析2017年1月~2018年6月北京大学第三医院颈椎专业组收治的306例行颈椎前路融合手术的颈椎退行性疾病患者的临床资料。在影像归档和通信系统(picture archiving and communication system,PACS)上测量C2~C7.椎体中横断面的CT值,通过双能X线吸收法(dual-energy X-ray absorptiometry,DXA)获得L1~L4总的骨密度T值。在术后第2天、术后3个月颈椎中立侧位X线片上分别测量颈椎前路融合节段前、后缘高度和融合节段Cobb角。定义术后3个月较术后2d融合节段前、后缘高度丢失的平均值≥2mm为内置物发生沉降。采用Spearman秩相关检验腰椎骨密度T值与C2~C7椎体CT均值的相关性,采用Spearman秩相关检验C2~C7椎体CT均值、腰椎骨密度T值分别与融合节段高度丢失数值、融合节段Cobb角改变的相关性。采用Logistic回归模型,分别检验C2~C7椎体CT均值、腰椎骨密度T值与沉降的关联。以沉降为标准,采用受试者工作特征(ROC)曲线确定C2~C7椎体CT均值的临界值。结果:术后3个月明确发生沉降122例,未发生沉降184例,沉降发生率为39.9%。C2~C7椎体CT均值与腰椎骨密度T值呈显著正相关(r=0.518,P<0.001),与融合节段Cobb角改变有显著相关性(r=-0.170,P=0.003),呈负相关。但腰椎骨密度T值与融合节段Cobb角改变无显著相关性(P=0.605)。融合节段高度丢失值与C2~C7椎体CT均值无显著相关性(P=0.056),与腰椎骨密度T值无显著相关性(P=0.274)。采用Logistic回归模型,控制性别、术式和节段的影响后,内置物沉降与C2~C7椎体CT均值有显著相关性(P=0.035),CT值每升高1HU,沉降风险降低0.4%(OR=0.996,95%CI:0.992~1.000);控制性别、术式和节段的影响后,内置物沉降与腰椎骨密度T值的无显著相关性(P=0.098)。以沉降为标准,采用ROC曲线分析,曲线下面积为0.562,ROC曲线上最佳C2~C7椎体CT均值为273HU。结论:预测颈椎前路融合术后早期内置物沉降时颈椎椎体CT值要优于腰椎骨密度T值,术前较高的颈椎椎体CT值患者术后发生内置物沉降的,风险较低。

Objectives:To investigate the application of CT value of cervical vertebrae in predicting early internal plant subsidence after anterior cervical fusion.Methods:A retrospective analysis was performed on 306 patients with cervical degenerative diseases who underwent anterior cervical fusion surgery from January 2017 to June 2018 in the Cervical Spine Group of Orthopaedic Department of the Third Hospital of Peking University.The CT values of cross-sectional C2-C7 vertebrae were measured on the picture archiving and communication system(PACS),and the total bone mineral density(BMD)T values of L1-L4 were obtained by dual-energy X-ray absorptiometry(DXA).The heights of the anterior and posterior edges of the fusion segment and the Cobb angle were measured on neutral lateral radiograph of cervical spine on day 2 and at month 3 after operation.The average height loss of the anterior and posterior edges of the fusion segment≥2mm between 3 months and 2 days after surgery was defined as subsidence of the implant.Spearman's rank correlation was used to test the correlation between the lumbar BMD T value and the C2-C7 CT mean value,as well as the correlation between the C2-C7 CT mean value,the lumbar BMD T value and the height loss and the Cobb angle change of fusion segments,respectively.Logistic regression model was used to test the correlations between the C2-C7 CT mean value,the lumbar T value and the subsidence.Taking subsidence(≥2mm)as the standard,the critical value of C2-C7 CT mean value was determined by using the receiver operating characteristic(ROC)curve.Results:There were 122 cases of subsidence and 184 cases of non-subsidence at 3 months after operation.The incidence rate of subsidence was 39.9%.There was a significant positive correlation between the C2-C7 CT mean value and the lumbar T value(r=0.518,P<0.001).There was a significant negative correlation between the C2-C7 CT mean value and the change of Cobb angle of the fusion segment(r=-0.170,P=0.003).However,there was no significant correlation between the lumbar T value and the change of Cobb angle of the fusion segment(P=0.605).There was no significant correlation between the height loss of the fusion segment and the C2-C7 CT mean value(P=0.056)or the lumbar T value(P=O.274).Using Logistic regression model,afer adjusting gender,operation style and segment,the correlation between the subsidence and the C2-C7 CT mean value was statistically significant(P-0.035),as an increase of per 1HU in CT value decreasing the subsidence risk by 0.4%(OR=0.996,95%CI:0.992-1.000);After adjusting gender,operation style and segment,the correlation between the subsidence and the lumbar T value was not statistically significant(P=0.098).Taking the subsidence as the standard,the area under the curve of ROC curve was 0.562,and the best C2-C7 CT mean value on the ROC curve was 273HU.Conclusions:The CT value of cervical vertebrae was superior to the lumbar T value when predicting the early subsidence of internal implants after anterior cervical fusion surgery.Patients with higher preoperative CT value of cervical vertebral had lower risk of implant subsidence after surgery.