The Effect of Bi-Cortical Screw Fixation for Subsidence and Cervical Alignment in Patients Undergoing Single-Level Anterior Cervical Discectomy and Fusion

Corresponding author: Woong Han Department of Neurosurgery, Nowon Eulji Medical Center, Eulji University School of Medicine, 68, Hangeulbiseok-ro, Nowon-gu, Seoul 01830, Republic of Korea Tel: +82-2-970-8312 Fax: +82-2-970-8313 E-mail: hanw881210@naver.com Objective: Anterior cervical discectomy and fusion (ACDF) is a treatment for cervical degenerative disease. However, there are few in vivo or long-term data sets including complete graft consolidation. This study aimed to verify the validity of bi-cortical screw fixation in patients undergoing ACDF. Methods: We enrolled 133 patients who underwent ACDF between February 2002 and March 2017. Patients were divided into the mono-cortical fixation group (group A) and bi-cortical fixation group (group B). Consecutive cervical radiography was performed. The end point of data collection was completion of fusion. We evaluated graft subsidence, the global cervical angle (C2-C7 Cobb’s angle), and segmental angle (SA; index level Cobb’s angle). Results: There were no significant differences or surgical level between groups A and B (graft type p= 0.292, surgical level p=0.065). However, types of plate were statistically different (plate type p-value=0.011), and the difference in subsidence between groups A and B was significant (group A, 3.946±2.43 mm; group B, 2.369±1.96 mm, p<0.001). In the logistic regression, bi-cortical screw fixation was found to be the most important factor contributing to subsidence reduction (β-coefficient, 1.002; odds ratio=2.725; p=0.012). There was a significant difference in the SA when fusion was achieved (group A, 2.14±5.05°; group B, 4.84±4.83°; p=0.002). The change in the SA (ΔSA) was significantly different between group A and group B (group A, ΔSA -4.42±4.04°; group B, ΔSA -1.15±3.64°; p=0.001). Conclusion: Bi-cortical screw fixation in ACDF led to reduced graft subsidence and a less kyphotic SA change.