title: A new concept for making decisions regarding the surgical approach for cervical ossification of the posterior longitudinal ligament: the K-line.
abstract: METHODS
  To report a new index, the K-line, for deciding the surgical approach for cervical ossification of the posterior longitudinal ligament (OPLL).
  
  
  OBJECTIVE
  To analyze the correlation between the K-line-based classification of cervical OPLL patients and their surgical outcome.
  
  
  BACKGROUND
  Previous studies showed that kyphotic alignment of the cervical spine and a large OPLL are major factors causing poor surgical outcome after laminoplasty for cervical OPLL patients. However, no report has evaluated these 2 factors in 1 parameter.
  
  
  METHODS
  The K-line was defined as a line that connects the midpoints of the spinal canal at C2 and C7. Twenty-seven patients who had cervical OPLL and underwent posterior decompression surgery were classified into 2 groups according to their K-line classification. OPLL did not exceed the K-line in the K-line (+) group and did exceed it in the K-line (-) group. By intraoperative ultrasonography, we evaluated the posterior shift of the spinal cord after the posterior decompression procedure. The Japanese Orthopedic Association scores before surgery and 1 year after surgery were evaluated, and the recovery rate was calculated.
  
  
  RESULTS
  Eight patients were classified as K-line (-), and 19 patients were classified as K-line (+). The mean recovery rate was 13.9% in the K-line (-) group and 66.0% in the K-line (+) group (P < 0.01). Ultrasonography showed that the posterior shift of the spinal cord was insufficient in the K-line (-) group.
  
  
  CONCLUSIONS
  The present results demonstrate that a sufficient posterior shift of the spinal cord and neurologic improvement will not be obtained after posterior decompression surgery in the K-line (-) group. Our new index, the K-line, is a simple and practical tool for making decisions regarding the surgical approach for cervical OPLL patients.
authors.affiliation: Spine Section, Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, Chuo-ku, Chiba, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Fujiyoshi
authors.forename: Masashi
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Junko
authors.initials: J
authors.lastname: Kawabe
authors.forename: Tomonori
authors.initials: T
authors.lastname: Endo
authors.forename: Takeo
authors.initials: T
authors.lastname: Furuya
authors.forename: Masao
authors.initials: M
authors.lastname: Koda
authors.forename: Akihiko
authors.initials: A
authors.lastname: Okawa
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Konishi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D019299:Decompression, Surgical / Q000379:methods* / Q000639:trends; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000601:surgery*; D011859:Radiography