Clinical Effects of Preoperative K-Line Tilt on Patient Outcomes After Laminoplasty for Cervical Ossification of the Posterior Longitudinal Ligament

Abstract

We sought to clarify the effects of the preoperative K-line tilt on cervical sagittal balance and patient outcomes after laminoplasty for cervical ossification of the posterior longitudinal ligament (OPLL). A retrospective analysis of 45 patients with OPLL treated by laminoplasty from January 2013 to December 2018 was performed. The radiological parameters included the K-line tilt, C2-C7 sagittal vertical axis, C2-C7 lordosis, T1 slope, and T1 slope minus C2-C7 lordosis. The patient quality of life outcomes were assessed using the neck disability index, Japanese Orthopaedic Association disability scale, and visual analog scale. The patients were classified into 2 groups according to the median preoperative K-line tilt angle (14.1°): the high K-line tilt group (n= 23) and the low K-line tilt group (n= 22). The postoperative cervical alignment changes and patient outcomes were compared and analyzed. The clinical outcomes demonstrated overall improvement at the final follow-up. The C2-C7 lordosis had significantly decreased from 13.5° ± 9.5° preoperatively to 10.2° ± 9.7°. The C2-C7 lordosis was less in the high K-line tilt group than that in the low K-line tilt group. In addition, the high K-line tilt group revealed significantly greater kyphotic changes and a greater loss of cervical lordosis compared with the low K-line tilt group. Finally, the quality of life outcomes and postoperative visual analog scale scores were higher in the high K-line tilt group. The results of the present study have shown that the parameter K-line tilt is an ideal radiological parameter for predicting the outcomes and determining the need for laminoplasty for cervical ossification of the OPLL. Patients with a higher K-line tilt preoperatively experienced more kyphotic alignment changes and neck pain after laminoplasty.