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

English Keywords:Anterior cervical fusion surgery  Subsidence  CT value  T value  Bone mineral density

English Abstract:

  【Abstract】 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=0.274). Using Logistic regression model, after 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.