The Relationship between the Occipitocervical Junction and Thoracic Kyphosis in Ankylosing Spondylitis: A Retrospective Cohort Study of 86 Cervical Fractures in Surgically Treated Patients

Abstract

Study DesignRetrospective analysis of prospectively collected data.PurposeTo describe the radiological characteristics of the occipitocervical area in patients with ankylosing spondylitis (AS) using the novel measure X-angle and to describe the correlation between the ankylosed occipitoatlantoaxial (OAA) joint and thoracic kyphosis (TK).Overview of LiteratureAS affects the axial skeleton, leading to progressive ankylosis of all vertebral segments. The effect of ankylosis on the upper cervical area of these patients is not well documented.MethodsAll patients with complete ankylosis of the spinal column between C3 and T1, treated for cervical spinal fracture between 2007 and 2014, were eligible for inclusion in this study. The level of cervical fracture was identified. The T1–12 and T5–12 angles were measured using preoperative lateral radiography. The progressive degeneration of the C0-C1-C2 joints was evaluated via the new indicator X-angle, through the measurement of the angle of the C0-C1-C2 articulations in the coronal plane using computed tomography.ResultsWe included 86 consecutive patients with AS (67 males) aged 69±12 years. The patients were divided into two groups according to the degenerative change in the C0–C1 joint (62 patients with a mobile joint and 24 patients with an ankylosed joint). There was no significant difference between the two groups in terms of age (p =0.094) and level of fracture (p =0.949). The most commonly affected level was C6. There was no requirement for revision due to non-union in any of the patients. There was a statistically significant difference observed in the T1–12, T5–12, and X-angles (p =0.004, 0.001, and <0.001, respectively). TK was greater in the ankylosed joint group than in the mobile joint group. The X-angle was also greater in the ankylosed joint group because of the vertical destruction of the OAA joint.ConclusionsThoracic hyperkyphosis resulted in degenerative changes in the C0-C1-C2 joint in patients with AS. The X-angle is a reliable method for measuring the integrity of the C0-C1-C2 joint in such patients.

Relationship between Sagittal Alignment and Anterior Bony Resorption of Cervical Vertebral Body in Patients with Ankylosing Spondylitis

“…Adaptive remodeling of the deformed cervical spine is well observed in patients with AS with severe thoracolumbar kyphosis. The change in mechanical loading may be one control stimulus to enhance the remodeling activities involving mechanisms (e.g., bone growth, absorption, and reinforcement) [9,10]. Superficial erosions of the anterior surfaces of the cervical vertebral bodies, so-called "anterior spondylitis", are known in AS and account for the characteristic "squaring" of the vertebral bodies [11][12][13].…”