The Importance of Incorporating Proportional Alignment in Adult Cervical Deformity Corrections Relative to Regional and Global Alignment

Abstract

Study Design/Setting. Retrospective single-center study. Background. The global alignment and proportion score is widely used in adult spinal deformity surgery. However, it is not specific to the parameters used in adult cervical deformity (ACD). Purpose. Create a cervicothoracic alignment and proportion (CAP) score in patients with operative ACD. Methods. Patients with ACD with 2-year data were included. Parameters consisted of relative McGregor’s Slope [RMGS = (MGS × 1.5)/0.9], relative cervical lordosis [RCL = CL – thoracic kyphosis (TK)], Cervical Lordosis Distribution Index (CLDI = C2 – Apex × 100/C2 – T2), relative pelvic version (RPV = sacral slope – pelvic incidence × 0.59 + 9), and a frailty factor (greater than 0.33). Cutoff points were chosen where the cross-tabulation of parameter subgroups reached a maximal rate of meeting the Optimal Outcome. The optimal outcome was defined as meeting Good Clinical Outcome criteria without the occurrence of distal junctional failure (DJF) or reoperation. CAP was scored between 0 and 13 and categorized accordingly: ≤3 (proportioned), 4–6 (moderately disproportioned), >6 (severely disproportioned). Multivariable logistic regression analysis determined the relationship between CAP categories, overall score, and development of distal junctional kyphosis (DJK), DJF, reoperation, and Optimal Outcome by 2 years. Results. One hundred five patients with operative ACD were included. Assessment of the 3-month CAP score found a mean of 5.2/13 possible points. 22.7% of patients were proportioned, 49.5% moderately disproportioned, and 27.8% severely disproportioned. DJK occurred in 34.5% and DJF in 8.7%, 20.0% underwent reoperation, and 55.7% achieved Optimal Outcome. Patients severely disproportioned in CAP had higher odds of DJK [OR: 6.0 (2.1–17.7); P=0.001], DJF [OR: 9.7 (1.8–51.8); P=0.008], reoperation [OR: 3.3 (1.9–10.6); P=0.011], and lower odds of meeting the optimal outcome [OR: 0.3 (0.1–0.7); P=0.007] by 2 years, while proportioned patients suffered zero occurrences of DJK or DJF. Conclusion. The regional alignment and proportion score is a method of analyzing the cervical spine relative to global alignment and demonstrates the importance of maintaining horizontal gaze, while also matching overall cervical and thoracolumbar alignment to limit complications and maximize clinical improvement.