Association of Spinal Alignment Correction With Patient-Reported Outcomes in Adult Cervical Deformity: Review of the Literature

OBJECTIVE: Adult cervical deformity (ACD) is a debilitating spinal condition that causes significant pain, neurologic dysfunction, and functional impairment. Surgery is often performed to correct cervical alignment, but the optimal amount of correction required to improve patient-reported outcomes (PROs) are not yet well-defined. METHODS: A review of the literature was performed and Fisher z-transformation (Zr) was used to pool the correlation coefficients between alignment parameters and PROs. The strength of correlation was defined according to the following: poor (0 <r ≤ 0.3), fair (0.3 < r ≤ 0.5), moderate (0.5 < r ≤ 0.8), and strong (0.8 < r ≤1). RESULTS: Increased C2–7 sagittal vertical axis was fairly associated with increased Neck Disability Index (NDI) (pooled Zr=0.31; 95% confidence interval [CI], -0.03 to 0.58). Changes in T1 slope minus cervical lordosis poorly correlated with NDI (pooled Zr=-0.04; 95% CI, -0.23 to 0.30). Increased C7–S1 was poorly associated with worse EuroQoL 5-Dimension (pooled Zr=-0.22; 95% CI, -0.36 to -0.06). Correction of horizontal gaze did not correlate with legacy metrics. Modified Japanese Orthopedic Association correlated with C2-slope, C7–S1, and C2–S1. CONCLUSION: Spinal alignment parameters variably correlated with improved health-related quality of life and myelopathy after corrective surgery for ACD. Further studies evaluating legacy PROs, Patient-Reported Outcomes Measurement System, and ACD specific instruments are needed for further validation.