Shunsuke Kanbara, Shiro Imagama, Keigo Ito, Kenyu Ito, Naoki Ishiguro, Fumihiko Kato

May 2018, Volume 27, Issue 6, pp 1416 - 1422 Original Article Read Full Article 10.1007/s00586-017-5246-9

First Online: 01 August 2017


The K line was introduced in a previous study, but did not include the cervical range of motion (ROM) as a parameter for evaluating surgical outcomes for patients with cervical ossification of the posterior longitudinal ligament (OPLL), and few reports have used both the K line and X-ray evaluations of the cervical ROM to describe the surgical outcomes in such patients.


Double-door C2–C7 or C3–C7 laminoplasty was performed in 100 patients with cervical OPLL who were classified according to the K line [86 patients, K line (+) and 14 patients, K line (−)]. Preoperative and 1-year postoperative Japanese Orthopedic Association (JOA) scores were used to evaluate recovery rates. Preoperative and postoperative C2–C7 lordotic angles were measured using the Cobb method. In addition, preoperative and postoperative sagittal alignments in flexion and extension were studied, and the flexion values were calculated by subtracting the preoperative and postoperative flexion ROM from extension ROM.


The mean JOA scores recovery rate were 57.3% in the K line (+) and 37.7% in the K line (−) groups (p < 0.05), and the respective corresponding mean postoperative C2–C7 lordotic angles were 9.1° and −3.4° (p < 0.001). In the K line (+) group, the JOA score recovery rate for a postoperative flexion value >0 was significantly lower than that for a postoperative flexion value ≤0 (p < 0.01), and the mean JOA score recovery rate worsened with an increased signal intensity on 1-year postoperative magnetic resonance imaging.


K line (+) patients exhibited sufficient neurological improvement after laminoplasty. However, even patients in this group had a low JOA score recovery rate if the postoperative flexion value was >0 and the 1-year postoperative increased signal intensity grade was 2 or 3.

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