title: Modified K-line in magnetic resonance imaging predicts insufficient decompression of cervical laminoplasty.
abstract: METHODS
  A retrospective single-center study.
  
  
  OBJECTIVE
  To clarify preoperative factors predicting unsatisfactory indirect decompression after laminoplasty in patients with cervical spondylotic myelopathy.
  
  
  BACKGROUND
  Many authors have shown that inadequate indirect decompression after laminoplasty can inhibit neural recovery and should be considered a complication. We previously demonstrated that residual anterior compression of the spinal cord (ACS) impaired recovery of upper extremity motor function. Although the K-line has been established as a predictive index indicating that laminoplasty is required in patients with ossification of the posterior longitudinal ligament, it remains unclear what preoperative factors can predict insufficient posterior cord decompression in patients with cervical spondylotic myelopathy.
  
  
  METHODS
  Forty-six consecutive patients who underwent laminoplasty for the treatment of cervical spondylotic myelopathy at our hospital were reviewed. A modified K-line was defined as the line connecting the midpoints of the spinal cord at C2 and C7 on a T1-weighted sagittal magnetic resonance image. We also determined the minimum interval between the tip of local kyphosis and a line connecting the midpoint of the cord at the level of the inferior endplates of C2 and C7 (INTmin) on the midsagittal image. Data analysis involved logistic regression and receiver operating characteristic curve analysis to select the most valuable index for predicting postoperative ACS.
  
  
  RESULTS
  Ten patients had ACS immediately after laminoplasty. Logistic regression analysis showed that INTmin was a significant predictive factor for the occurrence of postoperative ACS (odds ratio = 0.485; 95% confidence interval = 0.29-0.81; P = 0.02). Receiver operating characteristic curve analysis showed an area under the curve of 0.871. A cutoff of 4.0 mm had a sensitivity of 80% and a specificity of 80.6% for prediction of postoperative ACS.
  
  
  CONCLUSIONS
  The parameter INTmin correlated with the occurrence of postoperative ACS. A cutoff point of 4.0 mm is most appropriate for alerting spine surgeons to a high likelihood of postoperative ACS.
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirai
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yamada
authors.forename: Masato
authors.initials: M
authors.lastname: Yuasa
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Enomoto
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Yoshii
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kato
authors.forename: Shigenori
authors.initials: S
authors.lastname: Kawabata
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Inose
authors.forename: Atsushi
authors.initials: A
authors.lastname: Okawa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D019299:Decompression, Surgical / Q000379:methods*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011859:Radiography; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013117:Spinal Cord Compression / Q000000981:diagnostic imaging / Q000601:surgery*; D055009:Spondylosis / Q000000981:diagnostic imaging / Q000601:surgery; D016896:Treatment Outcome