[Evaluation of peroperative measurement system in the follow-up of vertebral displacements].
A computer assisted surgery system has been developed to quantify the vertebral displacements induced by the Cotrel-Dubousset instrumentation and to visualize in 3-D the spine at different per-operative steps. This spinal surgery is realized to correct idiopathic scoliosis. Per-operative measurements are obtained by using a magnetic digitizer. Five points per thoracic vertebra and six points per lumbar vertebra are digitized. The method proposed estimates the location of the digitized points on a computer graphics 3-D model of vertebrae by a point-to-surface matching algorithm. The 3-D models are constructed before the surgery using multiplanar radiographic reconstruction technique (2 or 3 views) and geometric modeling methods. Computer tools permit the 3-D visualization of the spine peroperatively and the evaluation of clinical indices such as Cobb angles and vertebral rotations. The system includes 3 principal error sources: 2) reconstruction error; 2) digitizer error (digitizer precision) and 3) point-to-surface matching error. In order to validate the overall system, measurements have been simulated for 2 vertebrae and 2 digitizers of different precision, taking onto account the reconstruction error. For 5 and 6 digitized points per vertebra, the matching algorithm gives a RMS error of respectively 3.0 and 2.0 mm.
Brodeur
P
P
Institute de Génie Biomédical, Ecole Polytechnique, Montréal, Québec, Canada.
Dansereau
J
J
De Guise
J
J
Labelle
H
H
D001696:Biomechanical Phenomena; D004868:Equipment Failure; D006801:Humans; D016268:Internal Fixators; D007432:Intraoperative Period; D011856:Radiographic Image Enhancement; D012600:Scoliosis / Q000601:surgery*; D013813:Therapy, Computer-Assisted / Q000379:methods*; D014102:Torsion Abnormality