A Commentary on “Flexion K-Line Status Predicts Surgical Strategy in Multilevel Cervical Ossification of the Posterior Longitudinal Ligament” - No. 2025 Action/Completeness/Style Phrase

Sep 30, 2026

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Neurospine 2025 commentary by Yutaro Kanda addresses how flexion K-line (FK-line) status informs surgical strategy in multilevel cervical ossification of the posterior longitudinal ligament. The commentary explains the clinical role of the K-line and FK-line, reviews evidence linking K-line negativity and greater preoperative cervical ROM to poorer outcomes after laminoplasty, and highlights comparative findings between laminoplasty and laminectomy with fusion. It also discusses C5 palsy risk factors, emphasizing posterior instrumentation attention and the authors’ valuable contribution to ongoing surgical debate.

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A Commentary on “Flexion K-Line Status Predicts Surgical Strategy in Multilevel Cervical Ossification of the Posterior Longitudinal Ligament”

K-line and FK-line as decision tools

Comparative outcomes: laminoplasty vs laminectomy with fusion

C5 palsy and posterior cord shift

Conflict of Interest

Neurospine 2025;22(4):949-950. [https://doi.org/10.14245/ns.2551834.917](https://doi.org/10.14245/ns.2551834.917) Commentary Corresponding Author Yutaro Kanda [https://orcid.org/0000-0001-5538-5516](https://orcid.org/0000-0001-5538-5516) Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan [Email: ykanda221@gmail.com](Email: ykanda221@gmail.com) See the article “Flexion K-Line Status Predicts Surgical Strategy in Multilevel Cervical Ossification of the Posterior Longitudinal Ligament: A Multicenter Comparison of Laminoplasty and Laminectomy With Fusion” via [https://doi](https://doi). org/10.14245/ns.2551108.554. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ([https://creativecom](https://creativecom)[mons.org/licenses/by-nc/4.0/](mons.org/licenses/by-nc/4.0/)) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © 2025 by the Korean Spinal Neurosurgery Society Neurospine pISSN 2586-6583 eISSN 2586-6591 A Commentary on “Flexion K-Line Status Predicts Surgical Strategy in Multilevel Cervical Ossification of the Posterior Longitudinal Ligament: A Multicenter Comparison of Laminoplasty and Laminectomy With Fusion” Yutaro Kanda Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan Ossification of the posterior longitudinal ligament (OPLL) is not rare in East Asian countries such as Korea and Japan, with prevalence rates ranging from 1.9% to 4.0%.1 The K-line is an imaginary line drawn connecting the midpoint of the spinal canal at C2 and C7 in patients with cervical OPLL, helping surgeons decide the surgical approach and procedure. Cervical laminoplasty (LP) has demonstrated favorable neurological outcomes in patients with K-line (+) and multilevel OPLL, although K-line (-) patients could experience insufficient decompression and poor neurological recovery when treated by LP. Therefore, anterior cervical decompression and fusion (ACDF) or laminectomy with fusion (LF) is frequently selected in patients with K-line (-) and multilevel OPLL because of favorable neurological recovery.2 However, perioperative complications, such as dysphagia and graft complications, were more common when treated by ACDF compared to LF.2 Consequently, surgeons are more likely to choose posterior surgery for high-risk patients, such as patients of advanced age and/or comorbidities. The optimal surgical procedure for the cervical OPLL is still a matter of debate. Some patients with K-line (+) and multilevel OPLL after LP experience limited neurological recovery.3 There is a limit to the decision-making by the use ofK-line alone. This maybe because of the lack of dynamic factors. In fact, a retrospective study of 72 patients demonstrated large preoperative segmental range of motion (ROM) at the peak of the OPLL as an independent risk factor for poor surgical outcome after LP for K-line (+) OPLL.3 Another study of 45 patients with OPLL also demonstrated a preoperative C2–7 ROM of greater than 20° as the risk factor of poor clinical outcome.4 The authors5 conducted a multicenter study of 426 patients with multilevel cervical OPLL with a focus on the K-line at the flexion position (FK-line). As expected, FK-line (-) patients tended to have a more kyphotic alignment and a more severe spinal cord compression, which would result in poorer neurological recovery compared to FK-line (+) patients. These find [www.e-neurospine.org](www.e-neurospine.org) 949 ings are consistent with prior reports.6,7 In contrast to these reports, the authors5 compared clinical outcomes between LP and LF in a significant number of patients with FK-line (-), which should be commended. LF achieved better correction of sagittal alignment and greater posterior cord shift, le

FAQs

What is the K-line in cervical OPLL, and how is it used in surgical planning?

The K-line is an imaginary line connecting the midpoint of the spinal canal at C2 and C7 in patients with cervical OPLL. It helps surgeons decide the surgical approach and procedure.

Why does FK-line status matter for choosing laminoplasty versus laminectomy with fusion?

FK-line (-) patients tend to show a more kyphotic alignment and more severe spinal cord compression, leading to poorer neurological recovery than FK-line (+) patients. In the multicenter comparison, laminectomy with fusion achieved better sagittal correction and greater posterior cord shift with superior neurological outcomes.

What factors are associated with the development of C5 palsy in cervical spine surgery?

Greater posterior spinal cord shift is associated with C5 palsy, supported by in vivo and clinical studies. Additional risk factors discussed include correction angle exceeding 20° and C4–5 foraminal stenosis.

Sep 30, 2026

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