The Reversibility of Swan Neck Deformity in Chronic Atlantoaxial Dislocations

Study Design. Prospective case series and radiographical analysis. Objective. This study aimed to characterize the changes in subaxial alignment after surgical correction of occipitoaxial kyphosis, establish normal parameters, and report on clinical outcomes in a population of patients with chronic atlantoaxial dislocation patients presenting with swan neck deformities. Summary of Background Data. Swan neck deformity of the cervical spine is a term used to describe the simultaneous development of both abnormal kyphosis and hyperlordosis malalignments. Currently, there are no published series that discuss their outcomes after treatment and, more specifically, the subsequent changes that occur in the subaxial spine after the correction of the primary deformity in cases of chronic hyperkyphosis at the occipitoaxial segment. Methods. This was a prospective clinical and radiographical study in a population of patients with chronic atlantoaxial dislocation presenting with swan neck deformities. C0-C2 and C2-C7 angles were measured using plain radiographs pre- and postsurgery. The relationship between the alignment of the occipitoaxial joint and the subaxial cervical spine was evaluated. Japanese Orthopaedic Society scores were used to assess functional outcomes. Results. C0-C2 improved from a mean of -14.4 degrees (SD, 9.5 degrees) preoperatively to a mean of 7.8 degrees (SD, 1.0 degrees) postoperatively (P = 0.02). C2-C7 changed from a mean of 43 degrees (SD, 2.8 degrees) to a mean of 18.6 degrees (SD, 11.2 degrees) postoperatively (P = 0.02). A significant correlation was detected between the changes that occurred in the upper and lower cervical alignments (R-2 = 0.133; P < 0.01). Clinically, the Japanese Orthopaedic Society preoperative scores improved significantly to postoperative (P < 0.01). Conclusion. This study reports the novel auto-correction of subaxial abnormalities after treatment of the primary upper cervical deformity and delineates the relationship between these 2 occurrences, thus demonstrating the reversibility of such complex abnormalities. Furthermore, the clinical outcomes after surgical treatment of swan neck deformities secondary to atlantoaxial dislocation are favorable and associated with a low complication rate.