The interspinous method of posterior atlantoaxial arthrodesis. Thirty-six patients underwent C1-2 posterior wiring and fusion procedures over a 5-year period for unstable C-2 fractures (eight cases), unstable atlas-axis combination fractures (six cases), rheumatoid C1-2 instability (14 cases), os odontoideum (four cases), traumatic C1-2 ligamentous instability (three cases), or instability secondary to a C-2 tumor (one case). In each case, the atlantoaxial arthrodesis utilized sublaminar wire at C-1 and incorporated an iliac-crest strut-graft positioned between the posterior arches of C-1 and C-2, held in place by securing wire around the base of the spinous process of the axis. Follow-up examination was performed in all patients after a mean postoperative duration of 33.7 months. The technical aspects and clinical merits of this fusion procedure, which led to a 97% union rate (one nonunion) and minimal morbidity and mortality rates, are presented. 