What is a Right Distal Fusion Level for Prevention of Sagittal Imbalance in Multilevel Posterior Cervical Spine Surgery: C7 or T1?

Study Design: This was a retrospective cohort study. Objective: To evaluate the sagittal alignment and T1 slope after multilevel posterior cervical fusion surgery depending on the distal fusion level; C7 or T1, and find out the appropriate distal fusion level. Summary of Background Data: The sagittal balance of the cervical spine is known to be affected by cervical lordosis and Ti slope. However, T1 slope is not a constant parameter that can be frequently changed after the surgery. Furthermore, useful studies to help guide surgeons in decision-making as to the most appropriate distal level of fusion for cervical sagittal balance are very limited. Materials and Methods: From 2014 to 2015, 50 patients who underwent multilevel posterior cervical fusion surgery were evaluated and followed up for > 2 years. Group 1 was composed of 29 patients whose distal fusion level was C7. Group 2 was composed of 21 patients whose distal fusion level was T1. C1-C2 lordosis, C2-C7 lordosis, C2-C7 sagittal vertical axis (SVA), and T1 slope were measured on preoperative and the last follow-up. Results: In group 1, C2-C7 SVA (23.1 -> 30.4 mm, P= 0.043) was worsened, and T1 slope (22.3 -> 32.9 degrees, P=0.001) was increased after the surgery. In group 2, no significant change occurred in C2-C7 SVA after the surgery (25.3 -> 23.6 mm, P = 0.648). The last follow-up T1 slope was similar with preoperative T1 slope (22.7 -> 21.8 degrees, P= 0.04) in group 2. Conclusions: This study showed that sagittal alignment became worse after the multilevel posterior cervical surgery when distal fusion level was stopped at C7, which was associated with increase of Ti slope. However, when we extended the distal fusion level to T1, T1 slope was not changed after the surgery. Therefore, sagittal alignment was maintained after the surgery. On the basis of the results of this study, we recommend distal fusion extends to T1.