Hypothesis: The myelopathy-based cervical deformity (CD) thresholds will associate with patient-reported outcomes and complications. Materials and Methods: This study include CD patients (C2-C7 Cobb > 10°, CL > 10°, cervical sagittal vertical axis > 4 cm, or CBVA > 25°) with BL and 1-year (1Y) data. Modifiers assessed low (L), moderate (M), and severe (S) deformity: CL (L: >3°; M:-21° to 3°; S: <‒21°), TS-CL (L: <26°; M: 26° to 45°; S: >45°), C2-T3 angle (L: >‒25°; M:-35° to-25°; S: <‒35°), C2 slope (L: <33°; M: 33° to 49°; S: >49°), MGS (L: >‒9° and < 0°; M: ‒12° to ‒9° or 0° to 19°; S: < ‒12° or > 19°), and frailty (L: <0.18; M: 0.18-0.27, S: >0.27). Means comparison and ANOVA assessed outcomes in the severity groups at BL at 1Y. Correlations found between modifiers assessed the internal relationship. Results: One hundred and four patients were included in the study (57.1 years, 50%, 29.3 kg/m2). Baseline S TS-CL, C2-T3, and C2S modifiers were associated with increased reoperations (P < 0.01), while S MGS, CL, and C2-T3 had increased estimated blood lost (>1000ccs, P < 0.001). S MGS and C2-T3 had more postop DJK (60%, P = 0.018). Improvement in TS-CL, C2S, C2-T3, and CL patients had better numeric rating scale (NRS) back (<5) and EuroQOL 5-Dimension questionnaire (EQ5D) at 1 year (P < 0.05). Improving the modifiers correlated strongly with each other (0.213-0.785, P < 0.001). Worsened TS-CL had increased NRS back scores at 1 year (9, P = 0.042). Worsened CL had increased 1-year modified Japanese Orthopedic Association (mJOA) (7, P = 0.001). Worsened C2-T3 had worse NRS neck scores at 1 year (P = 0.048). Improvement in all six modifiers (8.7%) had significantly better health-related quality of life (HRQL) scores at follow-up (EQ5D, NRS, and Neck Disability Index). Conclusions: Newly proposed CD modifiers based on mJOA were closely associated with outcomes. Improvement and deterioration in the modifiers significantly impacted the HRQL.