title: Epidemiological survey of ossification of the posterior longitudinal ligament by using clinical investigation registration forms.
abstract: BACKGROUND
  In Japan, ossification of the posterior longitudinal ligament (OPLL) has been designated as an intractable disease by the Ministry of Health, Labour, and Welfare. Here we aimed to clarify the epidemiological characteristics of severe OPLL patients by analyzing a national registry of this disease that uses clinical investigation registration forms.
  
  
  METHODS
  We retrospectively investigated clinical investigation registration forms for 24,502 patients with OPLL. We examined the sex distribution, age of disease onset, period from disease onset to registration, family history, site of ossification as determined by plain radiographs, Japanese Orthopaedic Association score, and number of OPLL surgeries.
  
  
  RESULTS
  The male-to-female ratios were 2.7:1 and 1.9:1 for new and renewed registrations, respectively. The mean ages at disease onset were 61.1 and 59.7 years for new and renewed registrations, respectively. The mean periods from disease onset to registration were 2.6 and 8.4 years for new and renewed registrations, respectively. The percentages of new registrations with and without family history were 5.3% and 51.5%, respectively (unknown for 43.3%). Of the new registrations, 3511, 359, and 200 cases exhibited ossification in the cervical spine, thoracic spine, and lumbar spine, respectively; the corresponding numbers for renewed registrations were 13,710, 2484, and 1508. The Japanese Orthopaedic Association score was 9.9 ± 3.6 for new registrations, and the mean score recovery rate for renewed registrations was 6.0%. The number of OPLL surgeries was one or zero, two, three, four, or five for 21,785, 2167, 412, 99, and 39 patients, respectively, with 11.1% of all patients having undergone multiple surgeries.
  
  
  CONCLUSIONS
  This study offers new insight into the epidemiological characteristics of severe OPLL. In particular, we found that the age of disease onset was higher than previously reported, the period from disease onset to registration (surgery) was relatively short, and about 90% of the patients required only a single surgery.
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan; Department of Orthopaedic Surgery, Kitasato University Kitasato Institute Hospital, 5-9-1 Shirokane, Minato, Tokyo 108-8642, Japan; Investigation Committee on the Ossification of the Spinal Ligament of the Ministry of Health, Labor and Welfare, Japan.
authors: Takashi
authors: T
authors: Tsuji
authors: Department of Orthopaedic Surgery, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan; Investigation Committee on the Ossification of the Spinal Ligament of the Ministry of Health, Labor and Welfare, Japan.
authors: Kazuhiro
authors: K
authors: Chiba
authors: Department of Orthopaedic Surgery, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan.
authors: Naobumi
authors: N
authors: Hosogane
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors: Nobuyuki
authors: N
authors: Fujita
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors: Tomohiro
authors: T
authors: Hikata
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors: Akio
authors: A
authors: Iwanami
authors: Department of Advanced Treatment for Spine and Spinal Cord Disorders, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors: Kota
authors: K
authors: Watanabe
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors: Ken
authors: K
authors: Ishii
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan; Investigation Committee on the Ossification of the Spinal Ligament of the Ministry of Health, Labor and Welfare, Japan.
authors: Yoshiaki
authors: Y
authors: Toyama
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan; Investigation Committee on the Ossification of the Spinal Ligament of the Ministry of Health, Labor and Welfare, Japan.
authors: Masaya
authors: M
authors: Nakamura
authors: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan; Investigation Committee on the Ossification of the Spinal Ligament of the Ministry of Health, Labor and Welfare, Japan. Electronic address: morio@a5.keio.jp.
authors: Morio
authors: M
authors: Matsumoto
mesh_terms: D000328:Adult; D017677:Age Distribution; D017668:Age of Onset; D000368:Aged; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D019637:Orthopedic Procedures / Q000379:methods / Q000706:statistics & numerical data*; D017887:Ossification of Posterior Longitudinal Ligament / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000601:surgery*; D011379:Prognosis; D011859:Radiography / Q000379:methods; D012042:Registries; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D017678:Sex Distribution; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome