Proposal of a Cervical Sagittal Classification System to Guide Surgical Treatment for Adult Cervical Deformity: A MEANS Cohort Analysis

Retrospective analysis. To describe normative cervical sagittal alignment and to propose a classification system to guide clinical assessment and surgical planning. Optimizing alignment is a key goal of adult cervical deformity (ACD) surgery. The purpose of this study was to understand normative alignment utilizing an asymptomatic adult cohort and to formulate a classification system that would help identify the spinal regions contributing to the cervical deformity. A total of 468 asymptomatic adults (18-80&#xa0;yr) from five countries (USA, France, Japan, Singapore, and Tunisia) formed the Multi-Ethnic Alignment Normative Study (MEANS). The C2-C7 sagittal vertical axis (cSVA), T1 slope (T1S), and C2-C7 cervical sagittal angle (CSA; positive=kyphosis, negative=lordosis), and other sagittal parameters were measured. Linear regression was utilized to correlate the C2-C7 CSA to the T1 slope. Thresholds for the C2-C7 sagittal vertical axis and T1 slope were defined as mean+2 SD. Groups were compared using ANOVA with a Tukey post hoc test. &#x3c7; 2 analysis was used for categorical comparisons. Mean values for C2-C7 cervical sagittal angle were -0.4&#xb0; (12.7&#xb0;), T1 slope was 23.0&#xb0; (7.9&#xb0;), C2-C7 sagittal vertical axis was 19.1 (9.8). The highest mean segmental Cobb angle was 3.2&#xb0; (4.8), which was at the C4-C5 segment. The T1S-CSA mismatch was 22.6 (9.4) with an interquartile range of 9.5 to 35.7. Linear regression yielded a formula CSA=-1.1(T1S) + 24.5 ( R2 =0.45, P <.0001) which was simplified to CSA=25-T1S. Four alignment types (1A/1B/2/4) were observed in the MEANS cohort. Type 3 alignment was absent. Types 1A, 1B, 2, and 4 alignment showed significant differences across cervical, thoracic, and global sagittal parameters. We define normative cervical alignment utilizing the MEANS cohort and propose a classification system to identify the spinal region driving the cervical deformity. Types 1A-B represent well-compensated alignment. Types 2 and 3 were considered to have deformities in the cervical spine and thoracolumbar spine, respectively. Type 4 spines have a combined deformity. This can help guide surgeons to determine the appropriate region that should be addressed with surgery.