Correlation Of Preoperative K-line Tilt With Prognosis Of Double-door Cervical Laminoplasty For Ossifcation Of The Posterior Longitudinal Ligament

OBJECT:To investigate the correlation between the preoperative K-line tilt and the prognosis of patients with OPLL（Ossifcation of the posterior longitudinal ligament）undergoing double-opening LAMP（laminoplasty）and each cervical sagittal plane parameter.METHODS:Using a retrospective analysis,50 cervical kyphosis patients with K-line positive and no cervical kyphosis and undergoing double-opening LAMP from January 2017 to December 2020 were selected for the study.The cervical sagittal balance parameters,including K-line,K-line tilt,C2-C7 SVA（C2-C7 sagittal vertical axis）,CL（cervical lordosis）,T1 slope,and T1 slope-CL（T1 slope-cervical lordosis）,were recorded for each patient based on preoperative neutral lateral X-ray.The NDI（cervical disability index）of the patients 1 year after surgery and the cervical kyphosis change within 1year after surgery were recorded to measure the patients’ postoperative recovery.The patients were divided into 2 groups according to the median postoperative NDI score of 12.5: good prognosis group（n = 25）and poor prognosis group（n = 25）.The differences in individual cervical sagittal balance parameters and posterior convexity changes between the two groups were compared and analyzed.The relationship between postoperative NDI and each sagittal parameter was also investigated by linear correlation and linear regression.Finally,the degree of influence of each parameter on postoperative NDI was analyzed by multiple linear regression according to the cervical sagittal balance parameters that showed positive differences in comparison between groups.RESULTS:Clinical symptoms improved in all patients,and there were differences between the low and high NDI score groups in K-line tilt（8.91±4.66 vs.13.71±4.29）,C2-C7SVA（17.27±6.50 vs.24.9±6.71）,T1 slope（21.74±3.32 vs.24.32±4.69）There was no statistically significant difference in cervical kyphosis change after surgery（0 vs 0）;there was a strong linear correlation between each 2 of the 3 parameters,K-Line tilt,postoperative NDI,and C2-C7 SVA（r = 0.838,P = 0.000;r = 0.746,P = 0.000;r =0.779,P = 0.000）;the postoperative NDI score was used as the dependent variable by multiple Linear regression analysis yielded the equation Y = 0.846 X1 + 0.364 X2 +0.242 X3-10.744（Y = postoperative NDI score;X1 = K-line tilt;X2 = T1 slope;X3 =C2-C7 SVA;R2 = 0.746）,and the absolute values of the standardized coefficients Beta K-line tilt,C2-According to the linear regression equation,K-line tilt=19.43° and postoperative NDI score=25（R2=0.7028,p=0.000）.In addition,both CL and T1 slope were linearly correlated with T1 slope-CL（r =-0.721,p = 0.000;r = 0.590,p = 0.000）.CONCLUSIONS:1.the larger the values of preoperative K-line tilt,C2-C7 SVA,and T1 slope,the higher the NDI score and the worse the prognosis after double-opening LAMP in patients with cervical OPLL.2.The influence of preoperative K-line tilt,C2-C7 SVA,and T1 slope on the prognosis of patients with OPLL undergoing double-opening LAMP was decreasing in order.3.Each of preoperative K-line tilt,preoperative C2-C7 SVA,and postoperative NDI scores had a positive relationship,and K-line tilt could serve as a substitute for C2-C7 SVA and T1 slope when measuring preoperative cervical sagittal parameters for operative selection.4.When the preoperative K-line tilt >19.43°,the postoperative NDI score was >25and the prognosis was poor.Therefore,patients with large preoperative K-line tilt are not suitable for double-opening LAMP.5.Preoperative K-line tilt is not predictive of the cervical kyphosis change in OPLL patients undergoing double-opening LAMP at short-term follow-up.