A systematic review and meta-analysis of sagittal cervical spine parameters: Normative values, correlation with quality of life, and biomechanical modeling.

Background: The sagittal alignment of the cervical spine is pivotal for spinal biomechanics, head positioning, and overall spinal balance. This systematic review synthesizes the available evidence on sagittal cervical spine parameters, establishing normative values in asymptomatic populations, evaluating their correlation with health-related quality of life, and exploring biomechanical modeling to understand their functional implications. Methods: A systematic literature search was conducted in PubMed/MEDLINE (January 2010-May 2025) following PRISMA guidelines. Key cervical alignment parameters were identified, including C2-C7 Cobb angle, C2-C7 sagittal vertical axis (SVA), T1 slope (T1S), T1 slope minus cervical lordosis (T1S-CL), C2 slope, neck tilt, cranial tilt, and spino-cranial angle (SCA). After screening 500 articles, 20 studies meeting predefined inclusion criteria were analyzed. Data on normative values, correlations with HRQoL scores and findings from biomechanical modeling were extracted. A meta-analysis was performed to establish normative values in the asymptomatic population. Results: Normative values were derived from meta-analyses, and statistical correlations were used to link the cervical spine parameters under study to HRQoL metrics such as the Neck Disability Index (NDI), EuroQol 5 Dimension (EQ-5D), and Short Form-36 (SF-36). Deviations, particularly C2-C7 SVA > 40 mm and T1S-CL > 15-20°, were significantly associated with reduced HRQoL. Biomechanical modeling techniques, including finite element (FE) and multibody dynamics approaches, provide further insights into spinal loading and stress distribution in the setting of abnormal cervical spinal alignment. Conclusions: Quantitative evidence shows that cervical alignment is prognostically decisive rather than merely descriptive. Across several clinical cohorts, a C2-7 sagittal vertical axis > 40 mm or a T1-slope minus cervical-lordosis mismatch > 15-20° consistently predicted clinically meaningful disability as measured by NDI, EQ-5D and SRS-22. These thresholds, supported by biomechanical modelling, define actionable targets for surgical planning, rehabilitation and long-term follow-up. Standardized measurement protocols and patient-specific reference ranges are now the critical next steps to transform these radiographic markers into personalized care pathways and prospective interventional trials.