title: 3D video-based deformation measurement of the pelvis bone under dynamic cyclic loading.
abstract: BACKGROUND
  Dynamic three-dimensional (3D) deformation of the pelvic bones is a crucial factor in the successful design and longevity of complex orthopaedic oncological implants. The current solutions are often not very promising for the patient; thus it would be interesting to measure the dynamic 3D-deformation of the whole pelvic bone in order to get a more realistic dataset for a better implant design. Therefore we hypothesis if it would be possible to combine a material testing machine with a 3D video motion capturing system, used in clinical gait analysis, to measure the sub millimetre deformation of a whole pelvis specimen.
  
  
  METHODS
  A pelvis specimen was placed in a standing position on a material testing machine. Passive reflective markers, traceable by the 3D video motion capturing system, were fixed to the bony surface of the pelvis specimen. While applying a dynamic sinusoidal load the 3D-movement of the markers was recorded by the cameras and afterwards the 3D-deformation of the pelvis specimen was computed. The accuracy of the 3D-movement of the markers was verified with 3D-displacement curve with a step function using a manual driven 3D micro-motion-stage.
  
  
  RESULTS
  The resulting accuracy of the measurement system depended on the number of cameras tracking a marker. The noise level for a marker seen by two cameras was during the stationary phase of the calibration procedure ± 0.036 mm, and ± 0.022 mm if tracked by 6 cameras. The detectable 3D-movement performed by the 3D-micro-motion-stage was smaller than the noise level of the 3D-video motion capturing system. Therefore the limiting factor of the setup was the noise level, which resulted in a measurement accuracy for the dynamic test setup of ± 0.036 mm.
  
  
  CONCLUSIONS
  This 3D test setup opens new possibilities in dynamic testing of wide range materials, like anatomical specimens, biomaterials, and its combinations. The resulting 3D-deformation dataset can be used for a better estimation of material characteristics of the underlying structures. This is an important factor in a reliable biomechanical modelling and simulation as well as in a successful design of complex implants.
authors.affiliation: University of Basel, 4056 Basel, Switzerland. beat.goepfert@unibas.ch
authors.forename: Beat
authors.initials: B
authors.lastname: Göpfert
authors.forename: Zdzislaw
authors.initials: Z
authors.lastname: Krol
authors.forename: Marie
authors.initials: M
authors.lastname: Freslier
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Krieg
mesh_terms: D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000503:physiopathology*; D002138:Calibration; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods*; D008954:Models, Biological; D009038:Motion; D010388:Pelvis / Q000503:physiopathology*; D014741:Video Recording / Q000295:instrumentation* / Q000379:methods