Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2019 Feb;9(1):85-103.
doi: 10.1177/2192568217720421. Epub 2018 Aug 15.

A Systematic Review of Classification Systems for Cervical Ossification of the Posterior Longitudinal Ligament

Lindsay Tetreault  1   2   3 , Hiroaki Nakashima  1   4   3 , So Kato  1 , Michael Kryshtalskyj  1   2 , Nagoshi Nagoshi  1   5 , Aria Nouri  1   2 , Anoushka Singh  1   2 , Michael G Fehlings  1   2
Affiliations
Review

A Systematic Review of Classification Systems for Cervical Ossification of the Posterior Longitudinal Ligament

Lindsay Tetreault et al. Global Spine J. 2019 Feb.

Abstract

Design: Systematic review.

Objective: To conduct a systematic review to (1) summarize various classification systems used to describe cervical ossification of the posterior longitudinal ligament (OPLL) and (2) evaluate the diagnostic accuracy of various imaging modalities and the reliability of these classification systems.

Methods: A search was performed to identify studies that used a classification system to categorize patients with OPLL. Furthermore, studies were included if they reported the diagnostic accuracy of various imaging modalities or the reliability of a classification system.

Results: A total of 167 studies were deemed relevant. Five classification systems were developed based on X-ray: the 9-classification system (0.60%); continuous, segmental, mixed, localized or focal, circumscribed and others (92.81%); hook, staple, bridge, and total types (2.40%); distribution of OPLL (2.40%); and K-line classification (4.19%). Six methods were based on computed tomography scans: free-type, contiguous-type, and broken sign (0.60%); hill-, plateau-, square-, mushroom-, irregular-, or round-shaped (5.99%); rectangular, oval, triangular, or pedunculate (1.20%); centralized or laterally deviated (1.80%); plank-, spindle-, or rod-shaped (0.60%); and rule of nine (0.60%). Classification systems based on 3-dimensional computed tomography were bridging and nonbridging (1.20%) and flat, irregular, and localized (0.60%). A single classification system was based on magnetic resonance imaging: triangular, teardrop, or boomerang. Finally, a variation of methods was used to classify OPLL associated with the dura mater (4.19%).

Conclusions: The most common method of classification was that proposed by the Japanese Ministry of Health, Labour and Welfare. Other important methods include K-line (+/-), signs of dural ossification, and patterns of distribution.

Keywords: K-line classification; classification systems; dural ossification; ossification of the posterior longitudinal ligament; reliability.

PubMed Disclaimer

Conflict of interest statement

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Overview of search strategy.
Figure 2.
Figure 2.
Classification system proposed by the Japanese Ministry of Health, Labour and Welfare: continuous, segmental, mixed, and localized. From left to right: segmental, continuous, mixed, and localized type of OPLL on computed tomography. Derived from Chang (2006).
Figure 3.
Figure 3.
The K-line. The K-line is a straight line that connects the midpoints of the spinal canal at C2 and C7 on lateral cervical radiographs. From left to right, K-line (+), K-line (−), K-line (+), K-line (−), K-line (−). Arrowheads on the right 2 radiographs indicate where the OPLL crosses the K-line. Derived from Fujiyoshi et al (2008).
Figure 4.
Figure 4.
Classification of ossification morphology: hill, plateau, and mushroom shaped.
Figure 5.
Figure 5.
Novel classification system proposed by Kawaguchi et al (2011) using 3-dimensional computed tomography.
Figure 6.
Figure 6.
Classification of OPLL based on the configuration of the compressed spinal cord: triangular, teardrop, and boomerang.
Figure 7.
Figure 7.
Types of dural ossification.
See this image and copyright information in PMC

References

    1. Matsunaga S, Sakou T. Ossification of the posterior longitudinal ligament of the cervical spine: etiology and natural history. Spine (Phila Pa 1976). 2012;37:E309–E314. - PubMed
    1. Stapleton CJ, Pham MH, Attenello FJ, Hsieh PC. Ossification of the posterior longitudinal ligament: genetics and pathophysiology. Neurosurg Focus. 2011;30(3):E6. - PubMed
    1. Nouri A, Tetreault L, Singh A, Karadimas SK, Fehlings MG. Degenerative cervical myelopathy: epidemiology, genetics, and pathogenesis. Spine (Phila Pa 1976). 2015;40:E675–E693. - PubMed
    1. Nakanishi T, Mannen T, Toyokura Y. Asymptomatic ossification of the posterior longitudinal ligament of the cervical spine. Incidence and roentgenographic findings. J Neurol Sci. 1973;19:375–381. - PubMed
    1. Aita I, Ohno A, Amagai H, Hirabayashi H, Hayashi K. Histomorphometric study of iliac bones in cervical myelopathy with ossification of the posterior longitudinal ligament. J Orthop Sci. 1998;3:324–329. - PubMed

LinkOut - more resources