C2 vs C3 as the Upper Instrumented Vertebra in Posterior Cervical Fusion: Effects on Junctional Mechanics and Midterm...

Selection of the upper instrumented vertebra (UIV) in posterior cervical decompression and fusion remains variable, and its influence on junctional mechanics and clinical outcomes is not fully defined. Extending fixation to C2 may offer mechanical advantages but introduces additional operative complexity. This study compared radiographic alignment, proximal junctional complications, and patient-reported outcomes between constructs terminating at C2 vs C3.

A retrospective cohort analysis was conducted on consecutive patients undergoing posterior cervical fusion from 2021 to 2023 with distal fixation at T1. Patients were stratified by UIV: C2 or C3. Demographic, operative, and radiographic data were collected. Cervical alignment parameters, proximal and distal junctional complications, and patient-reported outcomes (visual analog scale, Neck Disability Index, and 36-item Short Form physical component score and mental component score) were evaluated at baseline and at 6 and 24 months. Group comparisons used t and χ² tests, with significance set at P < 0.05.

A total of 104 patients were included (C2: n = 63; C3: n = 41) with comparable baseline demographics and clinical characteristics. Estimated blood loss was higher in the C2 group. Both groups demonstrated significant postoperative improvement in cervical alignment and patient-reported outcomes through 24 months, with no significant differences between groups for visual analog scale, Neck Disability Index, or physical component score. Constructs ending at C3 exhibited a significantly larger UIV - UIV + 1 angle and higher rates of proximal junctional failure (9.7% vs 0%), whereas distal junctional complication rates and overall revision rates were similar.

Termination at C2 reduces proximal junctional complications and results in a smaller transition angle without compromising midterm clinical outcomes; however, it involves greater operative burden. UIV selection should be individualized, favoring C2 when anatomical feasibility and junctional risk profiles support cranial fixation. Longer-term prospective studies are needed to determine whether mechanical advantages translate into durable clinical benefit.

These findings suggest that selecting C2 rather than C3 as the upper instrumented vertebra may reduce proximal junctional complications in posterior cervical fusion extending to T1, although the greater operative burden of C2 fixation should be considered when individualizing surgical planning.