title: Model studies on segmental movement in lumbar spine using a semi-automated program for volume fusion.
abstract: OBJECTIVE
  To validate a new non-invasive CT method for measuring segmental translations in lumbar spine in a phantom using plastic vertebrae with tantalum markers and human vertebrae.
  
  
  METHODS
  One hundred and four CT volumes were acquired of a phantom incorporating three lumbar vertebrae. Lumbar segmental translation was simulated by altering the position of one vertebra in all three cardinal axes between acquisitions. The CT volumes were combined into 64 case pairs, simulating lumbar segmental movement of up to 3 mm between acquisitions. The relative movement between the vertebrae was evaluated visually and numerically using a volume fusion image post-processing tool. Results were correlated to direct measurements of the phantom.
  
  
  RESULTS
  On visual inspection, translation of at least 1 mm or more could be safely detected and correlated with separation between the vertebrae in three dimensions. There were no significant differences between plastic and human vertebrae. Numerically, the accuracy limit for all the CT measurements of the 3D segmental translations was 0.56 mm (median: 0.12; range: -0.76 to +0.49 mm). The accuracy for the sagittal axis was 0.45 mm (median: 0.10; range: -0.46 to +0.62 mm); the accuracy for the coronal axis was 0.46 mm (median: 0.09; range: -0.66 to +0.69 mm); and the accuracy for the axial axis was 0.45 mm (median: 0.05; range: -0.72 to + 0.62 mm). The repeatability, calculated over 10 cases, was 0.35 mm (median: 0.16; range: -0.26 to +0.30 mm).
  
  
  CONCLUSIONS
  The accuracy of this non-invasive method is better than that of current routine methods for detecting segmental movements. The method allows both visual and numerical evaluation of such movements. Further studies are needed to validate this method in patients.
authors.affiliation: Department of Orthopaedics, Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden. per.svedmark@karolinska.se
authors.forename: P
authors.initials: P
authors.lastname: Svedmark
authors.forename: L
authors.initials: L
authors.lastname: Weidenhielm
authors.forename: G
authors.initials: G
authors.lastname: Nemeth
authors.forename: T
authors.initials: T
authors.lastname: Tullberg
authors.forename: M E
authors.initials: ME
authors.lastname: Noz
authors.forename: G Q
authors.initials: GQ
authors.lastname: Maguire
authors.forename: M P
authors.initials: MP
authors.lastname: Zeleznik
authors.forename: H
authors.initials: H
authors.lastname: Olivecrona
mesh_terms: D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D017116:Low Back Pain / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D009068:Movement / Q000502:physiology*; D012984:Software; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D025321:Surgery, Computer-Assisted