Comparison of imaging parameters pre- and post- reductive procedure for atlantoaxial dislocation via posterior fixation using pedicle screw and rod: a cross-sectional study

BACKGROUND: To compare the imaging parameters pre- and post- reductive procedure for atlantoaxial dislocation via posterior fixation using pedicle screw and rod. METHODS: Thirty-seven patients suffering from atlantoaxial dislocation underwent posterior reduction and internal fixation by pedicle screw and rod. We measured pre-operative and post-operative atlantodental interval (ADI), clivus-canal angle (CCA), cervicomedullary angle (CMA), sum of lateral mass interspace (SLMI) of the operation and the control group. ADI, CCA, CMA, and SLMI between the pre-operative and post-operative conditions of the operation group and the control group were compared. RESULTS: The ADI, CCA, CMA, and SLMI in the pre-operative condition of the operation group were 8.3 ± 4.3 mm, 130.2 ± 14.2°, 133.8 ± 16.7°, and 3.7 ± 1.3 mm, respectively, those in the post-operative condition of the operation group were 1.0 ± 0.9 mm, 148.5 ± 9.4°, 156.0 ± 8.2°, and 8.0 ± 2.7 mm, respectively, while those in the control group were 1.2 ± 0.3 mm, 152.7 ± 5.3°, 160.2 ± 6.3°, and 4.5 ± 1.0 mm respectively. Post-operative ADI, CCA, CMA, and SLMI were statistically different (p < 0.01) from pre-operative assessments. The SLMI has no significant difference between the pre-operative condition and the control group. Post-operative SLMI was statistically different from that of the control group. CONCLUSIONS: The lateral mass joints were widened after the anatomical reduction of atlantoaxial dislocation by pedicle screw and rod. Widening of the lateral mass exists in both atlantoaxial fusion and occipital-cervical fusion.