title: Reliability of low-radiation dose CT in the assessment of screw placement after posterior scoliosis surgery, evaluated with a new grading system.
abstract: METHODS
  A retrospective study.
  
  
  OBJECTIVE
  To evaluate the reliability of computed tomography (CT) with low radiation dose in the assessment of implant status in patients with adolescent idiopathic scoliosis (AIS).
  
  
  BACKGROUND
  The use of all-pedicle screw construct in scoliosis corrective surgery continues to gain increasing popularity since their introduction 1994 although their use in the thoracic spine carries a potential risk for neurovascular complications. CT is the method widely used to evaluate screw placement.
  
  
  METHODS
  Retrospective analysis of 46 consecutive low-dose spine CT in patients with AIS after posterior corrective surgery. Status of 809 titanium screws (642 thoracic) was evaluated. The degree of interobserver and intraobserver agreements about implant status was used as an indicator of the reliability of the low-dose spine CT in the assessment of accuracy of pedicle screw insertion. A new grading system has been developed for this purpose. Five types of misplacement have been evaluated: lateral, medial, and anterior cortical perforations; endplate perforation; and foraminal perforation.
  
  
  RESULTS
  The analysis has shown a substantial interobserver and intraobserver agreements (kappa: 0.69 and 0.76, respectively) in differentiating pedicle screws with acceptable placement from screws with partial or total cortical perforation. None of the examinations was subjectively classified as unreliable.
  
  
  CONCLUSIONS
  The study has shown that low-dose spine CT is a reliable method in evaluating screw placement in patients with AIS after posterior scoliosis surgery with titanium implants, using the here proposed grading system. The new grading system of screw misplacement was feasible and in line with the general agreement about the harmlessness of misplacement with minor pedicle breach. The reliability of low-dose spine CT in evaluation of lateral and medial cortical perforations was substantial. To reduce the radiation load, the postoperative assessment of titanium implants should be performed with low-dose CT.
authors.affiliation: Department of Radiology, Section of Neuroradiology, University of Lund, Malmö University Hospital, Malmo, Sweden. Kasim.Abul- Kasim@med.lu.se
authors.forename: Kasim
authors.initials: K
authors.lastname: Abul-Kasim
authors.forename: Anita
authors.initials: A
authors.lastname: Strömbeck
authors.forename: Acke
authors.initials: A
authors.lastname: Ohlin
authors.forename: Pavel
authors.initials: P
authors.lastname: Maly
authors.forename: Pia C
authors.initials: PC
authors.lastname: Sundgren
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D006801:Humans; D015588:Observer Variation; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*