Modified K-line in Magnetic Resonance Imaging Predicts Clinical Outcome in Patients With Nonlordotic Alignment After Laminoplasty for Cervical Spondylotic Myelopathy

Abstract

Retrospective single-center study. To investigate whether a preoperative index predicts clinical outcome after laminoplasty for cervical spondylotic myelopathy. This is the first study using the modified K-line, which connects the midpoints of the spinal cord at the C2 and C7 levels on midsagittal magnetic resonance imaging, to assess the relationship between postoperative clinical outcome and anticipated degree of spinal cord shifting. Sixty-one consecutive patients who underwent laminoplasty for the treatment of cervical spondylotic myelopathy between 2000 and 2011 at our hospital were retrospectively reviewed. The interval between the preoperative mK-line and the anterior structure of the spinal canal at each segment of the C3 to C6 levels (INTn, n = 3-6) were measured on sagittal T1-weighted magnetic resonance imaging, and the sum of the INTn (INTsum) was then calculated. The degree of posterior cord shift was defined as follows: %Csum = ΣCn; Cn = (Bn-An) × 100/An (n = 3-6; An and Bn represent the preoperative and postoperative intervals between the midpoint of the spinal cord and the anterior impingement at each segment on sagittal T1-weighted magnetic resonance imaging, respectively). In addition, we defined INTmin as the minimum interval of the INTn in each patient. All patients were divided into lordotic and nonlordotic groups on the basis of lateral neutral radiography. The Japanese Orthopaedic Association (JOA) scoring system and recovery rate of the JOA score for cervical myelopathy was evaluated as clinical outcomes. The recovery rate of the JOA score was 48.1%. The lordotic and nonlordotic groups contained 38 and 23 patients, respectively. Linear regression analysis revealed that INTmin was significantly correlated with the recovery rate of the patients in the nonlordotic group, whereas INTsum was not associated with recovery of the JOA score. We identified INTmin as a predictive factor for clinical outcomes in patients with nonlordotic alignment after laminoplasty. 4.