Multi-level posterior cervical-only fusion and instrumentation with versus without extension to C1: A short-term outcomes analysis using a large database.

Background Context: Few studies have compared outcomes of posterior cervical fusions and instrumentations with versus without extension to C1. Therefore, this study evaluates such 30-day adverse events, comparing multi-level constructs extending to C1 (C1) with subaxial fusions (SF) at C2 and below, to better define complication profiles. Methods: The ACS-NSQIP database (2014-2023) was queried for patients undergoing multi-level posterior cervical-only fusions and instrumentations using CPT codes 22600 (SF) and 22595 (C1), each paired with 22842. Cases with missing key variables or involving occiput, thoracic, or lumbar arthrodesis were excluded, and coding restrictions prevented cohort overlap. The primary outcome was any adverse event (AAE), with additional subgroup analyses. Propensity score matching (PSM) of relevant covariates balanced cohorts, with standardized mean differences <0.1 considered acceptable. Statistics included chi-squares, independent t-tests, multivariable regressions with odds-ratios (ORs), and threshold analyses, when appropriate. Results: Each cohort had 281 patients after PSM: SF (mean age=50.2±10.6; BMI=28.1±6.1 kg/m Conclusions: SF and C1 patients demonstrated plausibly comparable short-term outcomes, suggesting that extension of cervical-only fusion and instrumentation constructs through the atlantoaxial joint does not substantially increase early postoperative risk. Attention to perioperative timing may be warranted, and larger, longer-term studies are needed for corroboration. Level of Evidence: Level III.