Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P105. Limited morbidity and possible radiographic benefit of C2 versus subaxial cervical upper-most instrumented vertebrae

Abstract

BACKGROUND CONTEXT Use of cervical deformity (CD)-corrective instrumentation in the subaxial cervical spine is widely considered risky due to the narrow width of subaxial cervical pedicles and anatomy of the vertebral artery between C3 and C6. While C2 fixation provides increased biomechanical stability, the literature is sparse on guidelines indicating extension of CD-corrective fusion from the subaxial cervical spine to C2. PURPOSE Evaluate differences in alignment and clinical outcomes between surgical CD patients with subaxial upper-most instrumented vertebrae(UIV) and patients with UIV at C2. STUDY DESIGN/SETTING Retrospective review of prospective, multicenter CD database. PATIENT SAMPLE A total of 62 surgical CD patients (61±11 years, 65%F, BMI:30±9). OUTCOME MEASURES Cervical alignment parameters: cervical sagittal vertical axis (cSVA), C2–C7 cervical lordosis (CL), T1 slope minus CL (TS-CL). Upper cervical parameters: C0–C2 angle, slopes from C0, C1, and C2, McGregor's Slope (McGS). Clinical outcomes: EQ-5D, NDI, and mJOA questionnaires. METHODS Operative CD patients (C2–C7 Cobb>10°, CL>10°, cSVA>4 cm, or CBVA>25°) with baseline (BL) and 1-year postop (1Y) radiographic data, and cervical UIV>C2. Patients were grouped by UIV: C2 or subaxial (C3–C7) and propensity score matched(PSM) for BL cSVA. Mean comparison tests assessed differences in BL and 1Y patient-related, radiographic, and surgical data between UIV groups, as well as overall BL to 1Y changes in radiographic alignment and clinical outcomes. RESULTS PSM analysis included 62 patients (31 C2 UIV, 31 subaxial UIV) undergoing surgery for CD (7.4±3.6 lvls fused, 44% anterior approach, 19% posterior, 37% combined). Groups did not differ in BL comorbidity burden (P=0.175) or cervical sagittal alignment (cSVA,P=0.401). C2 UIV patients were older (64years vs. 58, P=0.040) and had longer fusions (10 lvls vs. 6, P 0.05); however, the overall cohort showed BL to 1Y increases in SVA (5 mm to 26, P=0.003) and TK (40°–44°, P=0.003). Flexibility of the cervical spine was maintained at 1Y regardless of UIV (CL flexibility was 15° between flexion and extension for C2 UIV and 17° for subaxial UIV, P=0.232). While both subaxial UIV and C2 UIV patients showed significant BL-1Y improvements in McGS (both p 0.05). Patients with C2 UIV showed higher operative complication rates (16% vs. 0%, P=0.020). CONCLUSIONS When presenting with similar preop cervical sagittal deformity, patients with instrumentation ending at C2 showed similar cervical range of motion and rates of reoperation, nonunion, and baseline to 1-year clinical outcome changes as patients with instrumentation ending in the subaxial cervical spine, though higher operative complication rates. Compared to subaxial UIV patients, C2 UIV patients showed greater baseline to 1-year horizontal gaze improvement, demonstrating the radiographic benefit and minimal clinical downside of extending fusion.