Sagittal re-alignment of the subaxial spine following occipitocervical fusion.

BACKGROUND 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 is to analyse the changes in the sagittal alignment of subaxial spine following occipito-cervical fixations. METHODS 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 CTscan. 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 by Auto CAD software 2010 version , and statistical analysis done by SPSS Statistics for Windows, Version 21.0. RESULTS The mean values were as follows: i) MG slope-pre op5.96 (SD=3.81); post op 9.42 (SD=9.6) [p=0.097],ii)O-C2 Pre op13.56(SD=10.58);Post op 14.67 (SD=10.66)[p=0.32], iii) C2-C7 Pre op23.71(SD=12.10); Post op18.29 ( SD=13.68)[0.128] iv) O-C7 Preop20.04(SD8.85);Post Op 25.33(SD=11.08)[p=0.069]and v)T1 slope Pre op 14.42(SD=10.68);Post op 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). Sub-grouping of fixation angles at O-C2 beyond 20 degrees had major changes in the subaxial spine which also percolated to the thoraco-lumbar spine. CONCLUSIONS Fixation angles of occipito-cervical spine do impact the sagittal alignment of the subaxial spine.