Sagittal realignment of the subaxial spine following occipito-cervical fusion.

Abstract

Sagittal imbalance after spine surgery may be a major source of pain and disability and this holds good even for highly mobile cervical region. However, very few studies have addressed the issue of the impact on adjacent and distant spinal segments following occipito-cervical fixations. The aim was to analyze the changes in the sagittal alignment of subaxial spine following occipito-cervical fixations. A total of 24 consecutive patients who underwent O-C2 fixation, with at least 2 years follow-up were retrospectively reviewed for changes in the parameters of sagittal alignment using mid-sagittal CT scan. Sagittal parameters, McGregor's line, O-C2 angle, C2-C7 angle, O-C7 angle and T1 slope were measured in pre- and at the final follow-up using Auto CAD software 2010 version (AutoDesk, Mill Valley, CA, USA); moreover, statistical analysis was done by using SPSS Statistics for Windows (IBM Corp., Armonk, NY, USA) version 21.0. The mean values were as follows: 1) MG slope preoperative: 5.96 (SD=3.81), postoperative: 9.42 (SD=9.6) (P=0.097); 2) O-C2 preoperative: 13.56 (SD=10.58), postoperative: 14.67 (SD=10.66) (P=0.32); 3) C2-C7 preoperative: 23.71 (SD=12.10), postoperative: 18.29 (SD=13.68) (0.128); 4) O-C7 preoperative: 20.04 (SD=8.85), postoperative: 25.33 (SD=11.08) (P=0.069); and 5) T1 slope preoperative: 14.42 (SD=10.68), postoperative: 16.58 (SD=8.78) (P=0.291). There was significant positive correlation (r=0.384, P=0.046) between cervical lordosis and T1 slope and a significant negative correlation between O-C2 and C2-C7 (r=-0.415, P=0.044). Subgrouping of fixation angles at O-C2 beyond 20 degrees had major changes in the subaxial spine which also percolated to the thoraco-lumbar spine. Fixation angles of occipito-cervical spine do impact the sagittal alignment of the subaxial spine.