title: A simple method for in vivo measurement of implant rod three-dimensional geometry during scoliosis surgery.
abstract: Scoliosis is defined as a spinal pathology characterized as a three-dimensional deformity of the spine combined with vertebral rotation. Treatment for severe scoliosis is achieved when the scoliotic spine is surgically corrected and fixed using implanted rods and screws. Several studies performed biomechanical modeling and corrective forces measurements of scoliosis correction. These studies were able to predict the clinical outcome and measured the corrective forces acting on screws, however, they were not able to measure the intraoperative three-dimensional geometry of the spinal rod. In effect, the results of biomechanical modeling might not be so realistic and the corrective forces during the surgical correction procedure were intra-operatively difficult to measure. Projective geometry has been shown to be successful in the reconstruction of a three-dimensional structure using a series of images obtained from different views. In this study, we propose a new method to measure the three-dimensional geometry of an implant rod using two cameras. The reconstruction method requires only a few parameters, the included angle θ between the two cameras, the actual length of the rod in mm, and the location of points for curve fitting. The implant rod utilized in spine surgery was used to evaluate the accuracy of the current method. The three-dimensional geometry of the rod was measured from the image obtained by a scanner and compared to the proposed method using two cameras. The mean error in the reconstruction measurements ranged from 0.32 to 0.45 mm. The method presented here demonstrated the possibility of intra-operatively measuring the three-dimensional geometry of spinal rod. The proposed method could be used in surgical procedures to better understand the biomechanics of scoliosis correction through real-time measurement of three-dimensional implant rod geometry in vivo.
authors: Division of Human Mechanical Systems and Design,Graduate School of Engineering, Hokkaido University, North 13 West 8 Kita-Ku, Sapporo, Japan 060-8628.
authors: Remel A
authors: RA
authors: Salmingo
authors: Shigeru
authors: S
authors: Tadano
authors: Kazuhiro
authors: K
authors: Fujisaki
authors: Yuichiro
authors: Y
authors: Abe
authors: Manabu
authors: M
authors: Ito
mesh_terms: D006801:Humans; D007432:Intraoperative Period; D055595:Mechanical Phenomena; D008962:Models, Theoretical; D019736:Prostheses and Implants; D012600:Scoliosis / Q000601:surgery*; D013131:Spine / Q000601:surgery