title: CT provides precise size assessment of implanted titanium alloy pedicle screws.
abstract: BACKGROUND
  After performing instrumented spinal fusion with pedicle screws, postoperative imaging using CT to assess screw position may be necessary. Stainless steel implants produce significant metal artifact on CT, and the degree of distortion is at least partially dependent on the cross-sectional area of the implanted device. If the same effect occurs with titanium alloy implants, ability to precisely measure proximity of screws to adjacent structures may be adversely affected as screw size increases.
  
  
  OBJECTIVE
  We therefore asked whether (1) CT provides precise measurements of true screw widths; and (2) precision degrades based on the size of the titanium implant imaged.
  
  
  METHODS
  CT scans performed on 20 patients after instrumented spinal fusion for scoliosis were reviewed. The sizes of 151 titanium alloy pedicle screws were measured and compared with known screw size. The amount of metal bloom artifact was determined for each of the four screw sizes. ANOVA with Tukey's post hoc test were performed to evaluate differences in scatter, and Spearman's rho coefficient was used to measure relationship between screw size and scatter.
  
  
  RESULTS
  All screws measured larger than their known size, but even with larger 7-mm screws the size differential was less than 1 mm. The four different screw sizes produced scatter amounts that were different from each other (p < 0.001).The amount of metal bloom artifact produced does increase as the size of the screw increases (rho = 0.962, p < 0.001).
  
  
  CONCLUSIONS
  CT of titanium alloy pedicle screws produces minimal artifact, thus making this the preferred imaging modality to assess screw position after surgery. Although the amount of artifact increases with the volume of titanium present, the degree of distortion is minimal and is usually less than 1 mm.
authors: Department of Pediatric Orthopedics, Children's Hospital Central California, Madera, CA, USA.
authors: Michael J
authors: MJ
authors: Elliott
authors: Joseph B
authors: JB
authors: Slakey
mesh_terms: D000497:Alloys; D000704:Analysis of Variance; D016477:Artifacts; D001863:Bone Screws; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D061330:Multidetector Computed Tomography; D011237:Predictive Value of Tests; D011474:Prosthesis Design; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D014025:Titanium; D016896:Treatment Outcome
chemical_list: D000497:Alloys; D014025:Titanium