Measurement And Clinical Significance Of K-line Tilt Following Adjacent Two-level Anterior Cervical Discectomy And Fusion

Objective:To investigate the relationships between classical sagittal alignment parameters and new parameter K-line tilt,and to study the significance of K-line tilt.Methods:A total of 72 patients following adjacent two-level ACDF were retrospectively analyzed.Radiographic measurements included:T1 slope(T1s),C2-7lordosis,segment angle(SA),C2-7SVA and K-line tilt.The neck disability index(NDI)scores were used to evaluate the clinical prognosis.Pearson correlation coefficient was calculated between radiographic measures.Linear regression analysis was used to analyze the relationships between follow-up K-line tilt and NDI.Results:?K-line tilt positively correlated with?T1s(r=0.650,p<0.05),?SA(r=0.269,p<0.05)and?C2-7SVA(r=0.293,p<0.05);?T1s positively correlated with?C2-7lordosis(r=0.428,p<0.05),?SA(r=0.631,p<0.01)and?C2-7SVA(r=0.235,p<0.05);?C2-7lordosis positively correlated with?SA(r=0.666,p<0.05),negatively correlated with?C2-7SVA(r=-0.467,p<0.01).The preoperative and postoperative K-line tilt were statistically significant(p<0.01),increasing from(7.50±6.48)oto(9.95±5.09)o.Preoperative NDI positively correlated with preoperative C2-7SVA(r=0.639,p=0.011)and K-line tilt(r=0.516,p=0.026);follow-up NDI positively correlated with follow-up T1s(r=0.664,p=0.038),C2-7SVA(r=0.756,p=0.004)and K-line tilt(r=0.832,p=0.006).The linear regression model showed that when follow-up K-lint tilt>23.75°,NDI>25(R~2=0.737,P=0.000).Conclusion:K-line tilt is also a important parameter like the C2–C7SVA.Particularly,K-line tilt greater than 23.75 corresponded to worse clinical prognosis,defined as NDI score greater than 25.