Effect of Cervical Mismatch on Sagittal Alignment and Patient Reported Outcomes in Long Posterior Cervical Fusions-A Multi-Center Analysis

Introduction: The dual purpose of this study was to, first, investigate the effect of T1 Slope and Cervical Lordosis (CL):T1-CL on outcomes in patients undergoing multi-level cervical fusions, and to establish a normative value of T1-CL in multi-level posterior cervical fusion.

Methods: Retrospective analysis of a multi-center database of patients undergoing of a ≥3 level posterior cervical fusion for cervical degeneration.

Results: 356 patients from seven different centers were included in analysis. Cohort demographics yielded mean age of 63 ±12 years with C3-C7 as the most frequently treated levels (42.3%). There was a strong correlation between T1 slope and C2-C7 CL (r=0.79), and a positive correlation between T1-CL and SVA (r=0.76), ODI (r=0.62) and VAS (r=0.65). Patients were then divided into 3 different groups based on the distribution ( < 25th, ≥25th& ≤75th and >75th percentile) of T1-CL data: Group 1, T1-CL < 34°; Group 2, 34°≥T1-CL≤56.4°; Group 3 T1-CL >56.4°. Group 1 had better alignment (20.6 mm), VAS (3.2) and ODI (32.6) as compared to Groups 2 (SVA 52.9, VAS 4.8, ODI 45.2) and 3 (SVA 70.4, VAS 5.4, ODI 47.4) at 2 years follow-up. SVA of Group 1 improved significantly more (pre vs last visit) than those in Groups 2 and 3. There was no difference in complication and revision rates between the three groups. Linear regression revealed that T1-CL demonstrated a constant value of 21.7° (r2=0.68, standard error 5.6°). A subgroup analysis of cohorts with T1-CLvalue between 21.7° and 34°, vs. others revealed a significant improvement in alignment, disability and pian (p < 0.05).

Conclusion : T1 slope and C2-C7 Cervical Lordosis and are strongly correlated, and when a parameter of T1 – CL is created, that value, in turn, is positively correlated with sagittal alignment (SVA), as well as pain (VAS) and disability scores (ODI). Patients with T1–CL values (between 21.7° and 34°) were significantly better aligned and reported less pain and lower disability scores. A range of T1-CL between 21.7° to 34° may be necessary to maintain horizontal gaze.