A Commentary on “The Role of K-Line and Canal-Occupying Ratio in Surgical Outcomes for Multilevel Cervical Ossification of the Posterior Longitudinal Ligament: A Retrospective Multicenter Study”

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Neurospine. 2025;22(2):349-350

Publication date (electronic) : 2025 June 30

doi : https://doi.org/10.14245/ns.2550870.435

Department of Neurosurgery, Brigham and Women’s Hospital, Dana Farber Cancer Institute, Boston, MA, USA

Corresponding Author John H. Chi Department of Neurosurgery, Brigham and Women’s Hospital/MGB, Harvard Medical School, 75 Francis St., Boston, MA, USA Email: jchi@bwh.harvard.edu

Ossification of the posterior longitudinal ligament (OPLL) is a frequently encountered condition causing cervical myelopathy with cord compression causing neurologic deficits. Unlike in most cases of cervical stenosis, where softer tissue from disc osteophyte complexes and/or ligament hypertrophy are the culprit, OPLL consists of much harder calcified soft tissues which often times is very adherent or even incorporated into the dura making decompression more challenging and higher risk. The debate between whether anterior, posterior or combination approaches is best for OPLL is longstanding and likely relies on situational factors to tailor the surgical plan to optimize success and minimize complications and adverse events.

To this end, the authors in this article [1] present a multicenter, retrospective series of 575 patients undergoing surgery for OPLL with minimum 2-year follow-up and report clinical outcomes in the context of a variety of radiographic/imaging measurements. The authors distill their findings down to a dichotomous categorization of canal-occupying ratio (COR) greater or less than 50% and K-line intersection presence or absence (defined as whether the OPLL crosses the line between midcanal at C2 and C7 on x-ray). They report that combining K-line and COR helps distinguish whether results will be better from and anterior or posterior approach.

The strengths of this study include the multicenter contributions as well as a relatively high number of patients. A wide range of surgeries were allowed, including anterior cervical discectomy and fusion with partial corpectomy (ACDF), anterior cervical corpectomy and fusion, laminoplasty and laminectomy with fusion, which represents the real-world options available to surgeons and a large number of radiographic parameters were measured. However, the majority of anterior procedures were ACDF which may indicate a lesser degree of OPLL as the stenotic portions are limited to the disc space itself and not behind the vertebral bodies (which presumably would have then required either corpectomy or posterior approach). This may be a selection bias giving an advantage to the anterior procedure given the relatively high success rate for ACDF in general and may have skewed results in favor of anterior approaches. Additionally, the combination of favorable K-line and low COR just indicates a “lesser” degree of OPLL and thus its predictive value may simply be a surrogate for degree of disease. The most interesting finding however is the authors observation that laminoplasty was best for high COR and positive K-line while laminectomy and fusion was favored for high COR but negative Kline. This deserves further study and the reasons for this finding is unclear.

Finally, the overall results of this study share some similaries and differences with a recent seminal paper published by Ghogawala et al. [2] in 2021. This randomized clinical trial showed results favoring posterior approaches for cervical spondylotic myelopathy, which is different but related to OPLL. Understanding how the results of both these studies can interact and complement each other will be important moving forward.

Notes

Conflict of Interest

The author has nothing to disclose.

References

1. Shin JJ, Yoo SJ, Kim DK, et al. The role of K-line and canaloccupying ratio in surgical outcomes for multilevel cervical ossification of the posterior longitudinal ligament: a retrospective multicenter study. Neurospine 2025;22:337–48.

2. Ghogawala Z, Terrin N, Dunbar MR, et al. Effect of ventral vs dorsal spinal surgery on patient-reported physical functioning in patients with cervical spondylotic myelopathy: a randomized clinical trial. JAMA 2021;325:942–51.

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