Clinical impact of 3-level anterior cervical decompression and fusion (ACDF) on the occipito-atlantoaxial complex: a retrospective study of patients who received a zero-profile anchored spacer versus cage-plate construct

To evaluate changes in the sagittal parameters of the occipito-atlantoaxial complex after three-level anterior cervical decompression and fusion (ACDF) and identify the influential factors by comparing ACDF with a zero-profile anchored spacer (ACDF-Z) versus a cage-plate construct (ACDF-P).The cohort comprised 106 patients who underwent three-level contiguous ACDF-Z or ACDF-P for cervical radiculopathy and/or myelopathy. Standing, flexion, and extension radiographs of cervical spine were obtained preoperatively, and 3 and 12 months postoperatively. The assessed cervical sagittal parameters were the platform angle of the axis, Cobb angle, and range of motion (ROM) of C2⁃7, C0⁃1, and C1⁃2.In both the ACDF-Z and ACDF-P groups, the Cobb angle of the upper cervical spine decreased and the C0-1 ROM increased from preoperatively to 3 and 12 months postoperatively (P < 0.01). The alignment restoration was lost at 12 months compared with 3 months in the ACDF-Z group, but not in the ACDF-P group (P < 0.01). The ACDF-P group showed more loss of C2-7 ROM and more compensatory changes in C0-2 ROM than the ACDF-Z group (P < 0.05).The Cobb angle decreased and ROM increased significantly as compensatory changes of the atlantooccipital or atlantoaxial joint after both types of ACDF, which may accelerate degeneration. The zero-profile anchored spacer had less impact on the occipito-atlantoaxial complex but was worse at maintaining the alignment restoration, which were contrary to the cage-plate construct. Surgeons should be aware of the impact of multi-level ACDFs on the occipito-atlantoaxial complex.