Prediction of incomplete decompression after cervical laminoplasty on magnetic resonance imaging: The modified K-line

The original K-line was developed on plain radiograph to predict incomplete indirect decompression for the patients with ossification of the posterior longitudinal ligament. The current study modified the K-line on magnetic resonance imaging (MRI) to determine risk factors for incomplete decompression after laminoplasty and to provide a guide for predicting incomplete decompression after laminoplasty and making decisions regarding the surgical approach in patients with cervical spondylotic myelopathy (CSM).

A retrospective review of 47 patients with CSM after laminoplasty was conducted. The modified K-line was defined as a line connecting both anterior points of the spinal cord at the level of the inferior vertebrae endplates of C2 and C7 on sagittal T1-weighted MR image. Quantitative analysis of the interval between the maximal anterior compression factor and the modified K-line (IAK) was performed to investigate the efficiency and practicality of this modified K-line. Data analysis involved logistic regression and Spearman rank correlation coefficient.

Thirteen patients (27.7%) had postoperative residual anterior compression of the spinal cord (ACS). Univariate logistic regression with backward stepwise procedure showed that only IAK (odds ratio: 0.301; 95% confidence interval: 0.134-0.673, P=0.003) was a significant risk factor for the occurrence of postoperative ACS. Incidence of ACS was 80% in patients with an IAK of less than 1.5mm and 96.2% in those whose IAK is 0mm.

The modified k-line can provide a guide for predicting poor clinical outcome after laminoplasty and making decisions regarding the surgical approach in patients with CSM.