Finite Element Study of Anterior Cervical Discectomy and Fusion Constructs Near Cervicothoracic Junction-Is T2 Modeling Necessary?

Cervical spine finite element (FE) models often terminate at T1, which may introduce boundary-induced alterations, particularly at the cervicothoracic junction (C7-T1). This is relevant in multilevel anterior cervical discectomy and fusion (ACDF) constructs that terminate at C7, leaving C7-T1 as the inferior adjacent segment. This study analyzes the biomechanical response of a three-level ACDF, which included the lowest cervical vertebra C7, using two FE models: a conventional C2-T1 model and an extended C2-T2 model. Postoperative range of motion (ROM) is evaluated under physiological flexion and extension loads of 2 N·m. A 7% increase in flexion ROM was observed in the C2-T2 ACDF model at C7-T1 when compared with the C2-T1 ACDF model. This change reflected the influence of shifting the inferior boundary to T2. The findings demonstrate that adding T2 preserved global kinematics, but the increase in the adjacent segment mobility (C7-T1) may lead to disc degeneration. The influence of rib and the responses under dynamic loading conditions have to be assessed for the use of caudal multilevel constructs in cervical spine modeling.