Relationship Between the Alignment of the Occipitoaxial and Subaxial Cervical Spine in Patients With Congenital Atlantoxial Dislocations

Study Design: Prospective radiographic analysis. Objective: This study aimed to characterize the relationship between the alignment of the occipitoaxial (OA) and the subaxial spine, establish normal parameters, and to determine the influence of upper cervical spine alignment on subaxial degenerative disc disease (DDD) and clinical outcomes in this population. Summary of Background Data: Previous studies reported that the alignments of the upper and lower cervical spine are closely interrelated in patients with atlantoaxial dislocations of a rheumatoid etiology. None have focused on congenital etiologies or included patients with OA kyphosis. The influence of the upper cervical alignment on subaxial (DDD) and outcomes is also unclear. Methods: Fifty-eight patients with congenital AAD undergoing surgical reduction and fusion were included. C0-C2 and C2-C7 angles were measured and DDD was assessed using plain radiographs. The relationship between the alignment of the OA joint and the subaxial cervical spine was evaluated, as well as the relationships between the cervical alignment, outcomes, and cervical DDD. Results: C0-2 improved from a mean of 1.59 +/- 17.3 degrees preoperatively to a mean of 15 +/- 9.8 degrees postoperatively (P < 0.001). C2-7 changed from a mean of 25.55 +/- 19.6 degrees to a mean of 14.2 +/- 14.4 degrees postoperatively (P < 0.001). The OA and subaxial alignment were negatively correlated in this population both before (r = -0.84; P < 0.001) and after (r = -0.64; P < 0.001) surgical treatment. There was an increased incidence of DDD postoperatively (P < 0.01), which was positively correlated with the postoperative C0-2 angle (r = 0.54; P < 0.001), but negatively correlated with the postoperative C2-7 angle (r = -0.79; P < 0.001). Conclusions: Changes in OA alignment before and after surgery are associated with changes in the subaxial spine. There is a high incidence of postoperative DDD in the subaxial spine that seems to be related to sagittal alignment after surgery.