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

• We developed and modified the K-line on sagittal T1-MRI image.
• We measured IAK to investigate the efficiency and practicality of this K-line.
• Patients with greater IAK values tended to have good neurologic outcome.
• ACS is almost inevitable when anterior compression factors beyond this K-line.
• This K-line can provide a guide for making decisions of the surgical approach.

ObjectivesThe 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).Patients and methodsA 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.ResultsThirteen 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 1.5 mm and 96.2% in those whose IAK is 0 mm.ConclusionThe 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.