Are Variable Screw Angle Change and Screw-to-Vertebral Body Ratio Associated With Radiographic Subsidence Following Anterior Cervical Discectomy and Fusion?

• Published in: Global spine journal 2024-05, p.21925682241252088
• Main Authors: Louie, Philip K, Kumar, Rakesh, Bansal, Aiyush, Raub, Spencer, Alostaz, Murad, Vivelo, Nicole, Gilbert, Michelle, Leveque, Jean-Christophe, Nemani, Venu
• Format: Article
• Language: English
• Subjects: Original Research
• ISSN: 2192-5682; 2192-5690
• DOI: 10.1177/21925682241252088

Retrospective Cohort. This study aims to assess the easily measurable radiographic landmarks of screw-to-vertebral body ratio and changes in screw angle to identify if they are associated with early subsidence following an Anterior cervical discectomy and fusion (ACDF). A retrospective cohort study was conducted on patients undergoing 1-3 level ACDF with allograft or PEEK cages. Preoperative, immediate postoperative, and 6-month postoperative radiographs were analyzed to measure intradiscal height (or distance between 2 vertebral bodies) as an anterior vertebral distance (AVD), middle (MVD), and posterior (PVD), screw angle, screw-to-vertebral body length ratio, and interscrew distance. Multivariate stepwise regression analyses were performed. 92 patients were included (42 single-level, 32 two-level, and 18 3-level ACDFs). In single-level ACDFs, a decrease in the caudal screw angle was associated with a decrease in AVD (=.001) and MVD ( = .03). A decrease in the PVD was associated with a decrease in segmental lordosis ( < .001). For two-level ACDFs, a higher caudal screw-to-body ratio was associated with a lower MVD ( = .01). Six months following an ACDF for degenerative pathology, a decrease in the caudal screw angle was associated with an increase in radiographic subsidence at the antero-medial aspect of the disc space albeit largely subclinical. This suggests that the caudal screw angle change may serve as a reliable radiographic marker for early radiographic subsidence. Furthermore, a greater screw-to-vertebral body ratio may be protective against radiographic subsidence in two-level ACDF procedures.