BACKGROUND CONTEXT The natural shift from a flexible lordotic to relatively fixed kyphotic spine demands special consideration in cervical deformity (CD) surgery. Rigid instrumentation may alter these dynamics considerably depending on a patient's primary driver of deformity and even apex of curvature. The lower instrumented vertebrae (LIV) in CD constructs may have varying effects on patient outcomes that are still poorly understood. PURPOSE To compare outcomes in CD patients undergoing instrumented correction according to the relation of LIV with primary driver of deformity. STUDY DESIGN/SETTING Retrospective review of a multicenter cervical fusion dataset. PATIENT SAMPLE Sixty-two patients undergoing cervical fusion. OUTCOME MEASURES Baseline (BL) and postop HRQLs: mJOA, NDI, EQ5D, Numeric Rating Scale for Neck/Back pain, distal junctional kyphosis (DJK) rate and magnitude. METHODS CD database inclusion: cervical kyphosis >10°, scoliosis (coronal Cobb>10°), positive cervical sagittal imbalance (cSVA>4 cm or TS-CL>10°), or CBVA>25°. Patients were stratified by primary driver of deformity: cervical (C) via Ames classification (TS-CL>20 or cSVA>40) and thoracic (T) via hyper/hypo-kyphosis (TK) from T4-T12 (60 10° LIV and LIV+2) rate up to 1 year. RESULTS Sixty-two CD patients (54.9 yrs, 62.8% F) were analyzed. Mean parameters at BL: TSCL 28.1, cSVA 26.9, T4-T12 angle 38.1. 21 pts had a C primary driver and 41 had a T primary driver by definition. One hundred percent of C primary drivers had LIVs below CL apex, while 9.2% of T primary drivers had LIVs below (caudal) to TK apex and 90.8% had LIVs above TK apex. No differences in HRQLs were found between C and T groups at BL and 3 mo postop. By 1 yr, C patients trended lower NDI (21.9 vs 29.0, p=0.245), lower NRS Neck pain (4.2 vs 5.1,p=0.358), and significantly higher EQ5D VAS (69.2 vs 52.4,p=0.040). When T pts with LIVs below TK apex were excluded, remaining T pts with LIV above apex had significantly higher 1 yr NDI than C pts (37.5vs21.9,p=.05). T patients also trended higher rates of postop DJK than C (19.5% vs 4.8%, p=0.119). No significant differences in mJOA were found (p>0.05). CONCLUSIONS Stopping prior to apex was more common in patients with a primary thoracic driver (T) and associated with deleterious effects. Those with a primary cervical driver (C) tended to have LIVs inclusive of CL apex with lower rates of post-op DJK. Additionally, T patients with LIVs above TK apex had significantly higher NDI and lower EQ5D VAS scores by 1-year. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.