A Biomechanical Analysis of Different Reconstruction Techniques Following Separation Surgery at the Cervicothoracic Junction: An In-Silico Analysis

Study Design: An in-silico study of the biomechanical behavior of the reconstructed spine after separation surgery at the cervicothoracic junction. Objective: To biomechanically compare different reconstruction techniques of the cervicothoracic junction after performing the separation surgery at the T1 level. Background: Separation surgery in spinal oncology refers to a technique where circumferential decompression and stabilization of the spinal cord are performed to provide enough space for safe delivery of higher doses of radiation. Separation at the cervicothoracic junction poses unique biomechanical challenges for reconstruction, given the transitional anatomy and high stress of this area. As such, the optimal reconstruction technique remains unclear. Materials and Methods: A cervical thoracic finite element model (C4–T3) was developed to test the biomechanical behavior of instrumented spine under 5 Nm moment. The separation surgery was simulated at T1, with instrumentation ranging up to two levels above and two levels below. Six unique constructs were tested to evaluate the effect of type of screw [pedicle screw (PS) versus lateral mass screw (LMS)] and levels of fixation. Results: Range of motion was not affected by the screw type. Longer fixation with LMS or PS resulted in greater resistance to motion and a stiffer spine. Screw stress was much higher than rod stress, and concentrated at construct end-points. Increasing length of thoracic endpoints did not reduce bony stress, while more than one level of cervical fixation suggested a protective effect on bone stress. PS fixation resulted in an additional protective effect on bone stress (30%) compared with LMS. Conclusion: The highest resistance to motion was observed in the two-above and two-below construct, irrespective of the type of screw. The use of PS suggested the greatest protective effect on bone stress. Selection of screw type and endpoint should be made with additional clinical considerations and requires future clinical verification.