Background: Ossification of the posterior longitudinal ligament (OPLL) is defined as ectopic bone formation within the posterior longitudinal ligament. Although various OPLL features (including the extent, shape, and thickness of the OPLL as well as the presence of dural ossification) have been defined in the literature, we are not aware of any systematic reviews that have summarized theassociationsbetween these featuresand clinical outcomes following surgery. The objective of the present study was to conduct a systematic review of the literature to determine whether OPLL characteristics are predictive of outcome in patients undergoing surgery for the treatment of cervical myelopathy. Methods: An extensive search was performed using 4 electronic databases: MEDLINE, MEDLINE In-Process, Embase, and the Cochrane Central Register of Controlled Trials. Our search terms were OPLL and cervical. We identified studies in English or Japanese that evaluated the association between cervical OPLL features and surgical outcome. The overall body of evidence was assessed with use of a scoring system developed by the Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group with recommendations from the Agency for Healthcare Research and Quality (AHQR). The present systematic literature review is formatted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Results: The search yielded a total of 2,318 citations. A total of 28 prognostic cohort studies were deemed relevant following a rigorous review process. Among them, only 7 retrospective studies involved a multivariate analysis that controlled for potential confounding variables. Sample sizes ranged from 47 to 133 patients. The main outcome was the postoperative Japanese Orthopaedic Association (JOA) score and/or recovery rate in 6 studies and the Nurick grade in 1. Of these, 2 were rated as Level-II evidence and 5 were rated as Level-III evidence. On the basis of our results, there was low evidence that patients with a hill-shaped ossification have a worse postoperative JOA score following laminoplasty than those with a plateau-shaped lesion; low evidence that the space available for the spinal cord cannot predict postoperative JOA scores; moderate evidence that there is no association between the occupying ratio and improvement on the Nurick scale; and insufficient evidence to determine the association between JOA outcomes and the type of OPLL, the presence of dural ossification, and the occupying ratio. Conclusions: Patients with hill-shaped OPLL have a worse postoperative JOA score than those with plateau-shaped ossification after laminoplasty. Because of limited evidence, it is unclear whether the occupying ratio, the type of OPLL, and the presence of dural ossification are predictive of surgical outcomes following either anterior or posterior decompression. A limited number of studies have used a multivariate analysis to evaluate the association between clinical outcomes and OPLL features. Additional studies representing high-quality evidence are needed. Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
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