1615. Limited Morbidity and Possible Radiographic Benefit of C2 vs Subaxial Cervical Upper-Most Instrumented Vertebrae
Authors: Peter Gust Passias; Cole Bortz, BA; Renaud Lafage, MS; Virginie Lagafe, PhD; Justin Smith, MD; Breton Line, BS; Robert Eastlack, MD; Daniel Sciubba, MD; Eric Klineberg, MD; Muhammad Burhan Janjua, MD (Brooklyn Heights, NY)
Introduction: Cervical deformity (CD)-corrective instrumentation in the subaxial cervical spine is widely considered risky due to the narrow width of subaxial cervical pedicles and vertebral artery anatomy. Fusion constructs ending at C2 provide biomechanical stability, but guidelines indicating extension of CD-corrective fusion from the subaxial spine to C2 are underexplored. This study evaluated differences in alignment and clinical outcomes between surgical CD patients with subaxial upper-most instrumented vertebrae(UIV) and patients with UIV at C2. Methods: Surgical CD patients(C2-C7 Cobb>10°, CL>10°, cSVA>4cm, 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 between UIV groups, as well as BL-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 comorbidity burden(P=0.175), cervical alignment(cSVA,P=0.401) or CL flexibility(C2:15° v subaxial:17°,P=0.232); however, C2 UIV patients were older(64yr vs 58,P=0.040) and had longer fusions(10 lvls vs 6,P<0.001).While both subaxial UIV and C2 UIV patients showed significant BL-1Y improvements in McGS(both P<0.030), C2 UIV patients improved to a larger degree(7.3° v 6.2°). Groups did not differ in complications, reoperation, pseudarthrosis, or BL-1Y changes in HRQLs(P>0.05). Those with C2 UIV showed higher operative complication rates(16% v 0%,P=0.020). Conclusion: Patients with instrumentation ending at the second cervical vertebra showed similar range of motion and rates of reoperation, non-union, and BL-1Y HRQL changes as patients with instrumentation ending in the subaxial cervical spine, though higher complication rates. Compared to subaxial UIV patients, C2 UIV patients showed greater BL-1Y improvements in horizontal gaze, demonstrating the increased radiographic benefit and minimal clinical downside of extending fusion constructs to C2.