Association between posterior C1-C2 fusion angle and postoperative subaxial sagittal alignment

Abstract

Objective To investigate the association between atlantoaxial (A-A) fusion angle and postoperative subaxial sagittal alignment so that an optimal fusion angle for preservation of physiologic subaxial alignment can be determined. Methods Ninety-two patients with A-A subluxation underwent several types of posterior A-A fusion from February 1995 to June 2005. Angles at C1-C2 and C2-C7 in the neutral position were measured before surgery and at the final foUow-up to find out any association between the post-oporative C2-C7 angle and the C1-C2 angle. Results All the 92 patients were followed up for 2.0 to 10.3 years, with an average of 5.2 years. The mean angles of C1-C2 and C2-C7 before surgery were 18.4° and 14.5° respectively, and 26.0° and 5.6° at the final follow-up respectively. In 30 patients, the follow-up angels were less than 20° (range, 10° to 20°); in 62 patients, the follow-up angels were larger than 20° (range, 20.0° to 43.6°) . Statistics revealed that when the fusion angles of C1-C2 were less than 20°, there was no association between the C1-C2 fixation angel and the postoperative C2-C7 angel; when the fusion angels of C1-C2 were larger than 20°, there was a linear negative association between the C1-C2 fixation angle and the C2-C7 postoperative angle. In addition, there was also a linear negative association between the pre/post-operative angles of C1-C2 and those of pre/pest-operative angles of the C2-C7. Conclusions Surgical fixation of A-A joint in a hyperlordotie position will make the lower cervical spine in a kyphotic sagittal alignment after surgery. The larger the C1-C2 fixation angle, the more kyphotic sagittal alignment of the lower cervical spine. To maintain the physiologic sagittal alignment of the subaxial cervical spine, C1-C2 should be fixed at an optimal fusion angle (range, 10° to 20°). Key words: Atlas; Axis; Aflantoaxial joint; Dislocation; Spinal fusion