Surgical Management of Cervical Ossification of the Posterior Longitudinal Ligament: Natural History and the Role of Surgical Decompression and Stabilization

Patrick A. Sugrue, M.D.; Jamal McClendon Jr., M.D.; Ryan J. Halpin, M.D.; John C. Liu, M.D.; Tyler R. Koski, M.D.; Aruna Ganju, M.D.

Disclosures

Neurosurg Focus. 2011;30(3):e3 

In This Article

Abstract and Introduction

Abstract

Object. Ossification of the posterior longitudinal ligament (OPLL) is a complex multifactorial disease process combining both metabolic and biomechanical factors. The role for surgical intervention and choice of anterior or posterior approach is controversial. The object of this study was to review the literature and present a single-institution experience with surgical intervention for OPLL.
Methods. The authors performed a retrospective review of their institutional experience with surgical intervention for cervical OPLL. They also reviewed the English-language literature regarding the epidemiology, pathophysiology, natural history, and surgical intervention for OPLL.
Results. Review of the literature suggests an improved benefit for anterior decompression and stabilization or posterior decompression and stabilization compared with posterior decompression via laminectomy or laminoplasty. Both anterior and posterior approaches are safe and effective means of decompression of cervical stenosis in the setting of OPLL.
Conclusions. Anterior cervical decompression and reconstruction is a safe and appropriate treatment for cervical spondylitic myelopathy in the setting of OPLL. For patients with maintained cervical lordosis, posterior cervical decompression and stabilization is advocated. The use of laminectomy or laminoplasty is indicated in patients with preserved cervical lordosis and less than 60% of the spinal canal occupied by calcified ligament in a "hill-shaped" contour.

Introduction

Ossification of the posterior longitudinal ligament (OPLL) is a pathological process whereby the PLL becomes progressively calcified, often leading to symptomatic spinal canal or foraminal stenosis.[11,29,31] It is a complex disease process, and patients often present to the spine surgeon in an advanced stage requiring surgical intervention. There is a great deal of evidence that OPLL is a multifactorial process resulting not only from inherent biological factors but also from environmental and biomechanical factors.[11,29,30,33] Each of these competing factors plays a role in the natural history of the disease process and ultimately in the role of surgical intervention. With that in mind, there are various potential surgical options available to the spine surgeon, each with its own risks, benefits, and accompanying pitfalls. In this manuscript, we discuss the various types of OPLL in the cervical spine and the advantages and disadvantages of different surgical strategies as supported by our institutional experience.

The prevalence of OPLL has been shown to be higher in East Asian countries, most significantly in Japan (1.9%–4.3%), Korea (3.6%), and Taiwan (2.8%).[11] The prevalence of OPLL in the North American Caucasian population has been reported as only 0.12% historically,[11] but more recently, Epstein[5] has reported that as many as 25% of patients who present with cervical myelopathy have some evidence of OPLL. While there is evidence of a genetic predisposition for OPLL there are also underlying associated metabolic comorbidities. Both adult-onset and non–insulin-dependent diabetes mellitus have been shown to be independent risk factors for OPLL and are believed to be related to an increase in insulin production and its upregulating effect on osteoprogenitor cells leading to OPLL.[1,11,20,27] Ossification of the PLL can also be seen in as many as 50% of cases of diffuse idiopathic skeletal hyperostosis (DISH).[5,7]

Four types of OPLL have classically been described:[10,25] 1) segmental—confined to the area posterior to the vertebral bodies without crossing the disc spaces; 2) continuous—extending from vertebral body to vertebral body including the disc space and spanning multiple levels; 3) mixed: combined aspects of both segmental and continuous types that maintains some skipped areas; and 4) other: limited to area behind the disc space with some extension to the posterior vertebral body endplate or focal punctate areas of hypertrophy/calcification of the posterior longitudinal ligament.

Although OPLL is the result of multiple processes, there have been numerous studies addressing the genetic and metabolic basis of this disease. While the details of those studies are beyond the scope of this manuscript, there are a few details that bear mentioning. The role of repeated mechanical stress to the cervical spine has been proposed as an agent in the formation of OPLL. Studies looking at the importance of dynamic repeated stress have demonstrated an increase in BMP-2, BMP-4, prostaglandin I2 synthase, and osteoblast specific transcription factors in patients with OPLL compared with those without OPLL.[11,12] The increase in these cytokines suggests, as the authors point out, that the mechanical stress induces a biochemical response that leads ultimately to osteogenic induction in the ligament cells leading to OPLL. The importance of this finding with respect to surgical intervention is important to point out in terms of the role of surgical stabilization as opposed to decompression alone.

Matsunagra et al.[22] studied the natural history of untreated OPLL and found that 17% of patients who were found to have OPLL without signs of myelopathy went on to progress to the development of myelopathy. Likewise, 64% of patients with signs of myelopathy at the time of presentation who did not undergo surgery experienced neurological deterioration. This clinical study helps to highlight the fact that the development and progression of OPLL is a dynamic process. Epstein[5] describes OPLL as part of a continuum that begins with increased vascular fibrosis of the PLL and progresses to focal calcification, proliferation of periosteal cartilage, and ultimately ossification. Early ossification is often seen in patients in the 5th decade of life in the area posterior to the disc space alone, making it difficult to distinguish from degenerative spondylosis. The rate of ossification is variable among different patient groups but Harsh et al.[8] found an annual growth rate of 0.67 mm in the anterior-posterior direction and 4.1 mm in the cranial-caudal direction. In another study, Matsunaga et al.[21] confirmed these findings, demonstrating that nearly 20% of patients with untreated OPLL experienced an increase of 2 mm or more in PLL thickness and 86% experienced an increase in the cranial-caudal extent of the disease. Murakami et al.[26] likewise report a case of a patient who progressed from asymptomatic segmental OPLL to a mixed-type OPLL as his neurological condition deteriorated, developing myelopathy over the course of 4 years. The progressive nature of OPLL suggests that most patient will ultimately require some sort of surgical intervention.

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