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Ossifi cation of the posterior longitudinal ligament (OPLL) is no longer only a Japanese
disease. In 2004, 18 papers on OPLL and related conditions were published, and 7 of
those were from countries other than Japan. Major textbooks on spine surgery, such
as The Spine, The Cervical Spine, and Spine Surgery, have devoted chapters to OPLL.
Although OPLL has been recognized as a distinct spinal disease entity, several questions
regarding etiology and treatment have remained unanswered.
In 2002, the Committee for Study of Ossifi cation of Spinal Ligaments, subsidized by
the Ministry of Health, Labour and Welfare and chaired by Professor K. Nakamura,
decided to systematically review papers on OPLL and related conditions. The purposes
were to direct the research activities of the committee more effectively and to provide
more certain knowledge about OPLL, in the form of clinical practice guidelines, for
general practitioners and for patients suffering from the condition. A committee for
this task was formed in cooperation with the Japanese Orthopaedic Association, and
clinical practice guidelines for OPLL, consisting of 4 chapters and 75 research questions,
were developed after almost 3 years. Unfortunately, the guidelines have been
published only in Japanese as of this writing. Therefore, 4 chapters of this book (“Overview
of Epidemiology and Genetics,” “Overview of Etiology and Pathogenesis,” “Diagnosis
of OPLL and OYL,” and “Overview of Treatment for Ossifi cation of the
Longitudinal Ligament and the Ligamentum Flavum”) were included as summaries of
the 4 chapters of the guidelines.
One of the important issues that arose during the development of the guidelines was
that of diagnostic criteria. OPLL was discovered before computerized tomography had
been devised; therefore, OPLL was diagnosed on the basis of clinical and roentgenographic
fi ndings from conventional imaging techniques such as plain roentgenography
or tomography. However, with an increase in the diversity of medical professionals
who take care of patients with spinal disease and with advances in imaging technology
such as computerized tomography, a small ossifi ed lesion that usually would not grow
to compress the spinal cord is sometimes diagnosed as OPLL, which confuses patients.
Diagnosis of OPLL has been made based on tactical knowledge—that is, knowledge
held by a closed society made up of experts in the fi eld. This is not a rare example.
Several common spinal diseases, such as cervical spondylotic myelopathy, lumbar disc
herniation, and lumbar canal stenosis, are diagnosed in this manner. The committee
has set tentative diagnostic criteria for OPLL until more defi nite criteria can be established
scientifi cally, and those tentative diagnostic criteria for OPLL are included in
this book.
Since 1997, when the fi rst edition of OPLL was published, research on OPLL has
progressed steadily in genetics and bone cell physiology. Genetic studies using a variety
of approaches, supported by nationwide collaboration, seem to be narrowing in on a
disease-related gene. The process of ossifi cation in this condition has been elucidated
by studies using techniques of bone cell physiology. Clinical studies using imaging and
electrophysiological modalities have clarifi ed the pathophysiology of the spinal cord
in OPLL. Follow-up studies have revealed long-term (more than 10 years) results of
surgical treatment of both posterior and anterior approaches. All the chapters have
been updated with these fi ndings. |
