The purpose of this study focuses on the changes of the syrinx volume after posterior reduction and fixation of the basilar invagination (BI) and atlantoaxial dislocation (AAD) with syringomyelia. We retrospectively analyzed the clinical outcome and syrinx volume changes in 71 patients with BI, AAD and syringomyelia treated with the posterior reduction and fixation technique. Clinical improvement was observed in 64 (90.1 %) patients postoperatively; 5 (7.0 %) were stable and 2 (2.8 %) were clinically aggravated. The postoperative Atlantodental interval became normal in 61 patients (86.0 %); showed reduction that was greater than 50 % but not complete in 5 patients (7.0 %); and reduction which was less than 50 % in 5 patients (7.0 %). The size of the syrinx was reduced postoperatively in 66 patients (93.0 %) while no change in the remaining 5 patients (7.0 %). Posterior reduction and fixation of the AAD and BI can effectively enlarge the foramen magnum, improve the cerebrospinal fluid circulation and consequently reduce the volume of the syrinx.
