Wu X, et al. - Experts gauged the incidence and risk factors for adjacent segment degeneration (ASD) following occipitoaxial fusion (OAF) for atlantoaxial instability (AAI) in non-rheumatoid arthritis (RA). In the non-ASD, a significantly greater difference between pre- and postoperative O-C2 angles was seen than that in the ASD group. Findings suggested the likeliness of malalignment of the cervical spine with under-correction of the O-C2 angle, resulting in the development of postoperative ASD, subaxial subluxation (SAS), and swan neck deformity.