title: A noninvasive, three-dimensional spinal motion analysis method.
abstract: METHODS
  A three-dimensional, noninvasive motion analysis method was developed by monitoring the orientation of the principal axes of each vertebra.
  
  
  OBJECTIVE
  To develop a method of performing three-dimensional, noninvasive motion analysis of the spine using computed tomography data.
  
  
  BACKGROUND
  The concept of using principal axes of the moment of inertia tensor to measure the orientation and position of a rigid body has been applied to the wrist and subtalar joints, but has not yet been applied to the spine.
  
  
  METHODS
  Scans were taken of two isolated vertebrae in various known positions. Centroids, area, moments, and product of inertia of each scan were determined using a commercial program. Custom software combined data using the parallel axis theorem to give three-dimensional data for each vertebra. Changes in the centroid and principal axes were used to calculate translation and rotation, respectively.
  
  
  RESULTS
  The system accuracy was within 1.0 degree in rotation and 1.0 mm in translation. Some errors occurred in minor motions when a smaller number of scans were used. System resolution was 0.43 mm.
  
  
  CONCLUSIONS
  A system has been developed capable of calculating three-dimensional spinal motion based on measurements of a series of computed tomography images. The system has an accuracy similar to that of current motion analysis methods, but future studies will be necessary to apply this system in vivo.
authors.affiliation: Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, USA.
authors.forename: T H
authors.initials: TH
authors.lastname: Lim
authors.forename: J C
authors.initials: JC
authors.lastname: Eck
authors.forename: H S
authors.initials: HS
authors.lastname: An
authors.forename: L M
authors.initials: LM
authors.lastname: McGrady
authors.forename: G F
authors.initials: GF
authors.lastname: Harris
authors.forename: V M
authors.initials: VM
authors.lastname: Haughton
mesh_terms: D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology*; D014057:Tomography, X-Ray Computed