title: A new method to determine whether ossified posterior longitudinal ligament can be resected completely and safely: spinal canal "Rule of Nine" on axial computed tomography.
abstract: OBJECTIVE
  To introduce the new method of spinal canal "Rule of Nine" on axial computed tomography (CT) to determine whether ossified posterior longitudinal ligament (OPLL) can be resected completely and safely.
  
  
  METHODS
  From January 2008 to January 2013, we retrospectively analyzed 308 patients with cervical OPLL who underwent anterior corpectomy. Patients were examined by cervical plain X-ray, CT, and magnetic resonance imaging. The characteristics of OPLL on axial CT, dural mater adhesion and ossification, complete resection of the ossified mass, cerebrospinal fluid (CSF) leakage, spinal cord injury (SCI), and postoperative outcome were all studied. OPLL was characterized at the maximum ossified level using spinal canal "Rule of Nine" on axial CT.
  
  
  RESULTS
  OPLL was completely and safely resected in 129 patients, whose ossified mass was within the safety zone. No CSF leakage or SCI occurred. The most ossified material was resected when OPLL was within the danger zone in 21 patients. There were two cases of SCI and seven of CSF leakage. In the other 158 patients, the ossified mass was within the intermediate zone. In 96 patients the width of the ossified mass was <2 resection units. It was completely resected and one case had CSF leakage. In the other 62 cases, the ossified mass was >2 resection units and there were nine cases of CSF leakage. CSF leakage and SCI increased significantly when the ossified mass was ≥6 units. The inter- and intraobserver κ values were 0.76 and 0.84, respectively, showing a good reliability.
  
  
  CONCLUSIONS
  Our new method can be used to determine whether OPLL can be resected completely and safely, and identify potential risks and complications.
authors.affiliation: Department of Orthopaedic Surgery, Changzheng Hospital, No. 415 Fengyang Road, Shanghai, 200003, China.
authors.forename: Haisong
authors.initials: H
authors.lastname: Yang
authors.forename: Xuhua
authors.initials: X
authors.lastname: Lu
authors.forename: Xinwei
authors.initials: X
authors.lastname: Wang
authors.forename: Deyu
authors.initials: D
authors.lastname: Chen
authors.forename: Wen
authors.initials: W
authors.lastname: Yuan
authors.forename: Lili
authors.initials: L
authors.lastname: Yang
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000328:Adult; D000368:Aged; D065634:Cerebrospinal Fluid Leak / Q000209:etiology; D003661:Decision Support Techniques; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000000981:diagnostic imaging / Q000601:surgery*; D011183:Postoperative Complications; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013115:Spinal Canal / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed