A NEW TECHNIQUE FOR THE 3-DIMENSIONAL STUDY OF THE SPINE IN-VITRO ANDIN-VIVO BY USING A MOTION-ANALYSIS SYSTEM

We introduce a new method with a motion-analysis system (MAS) to study the vertebral model in vitro. Compared with the currently most accura te technique, roentgen stereophotogrammetric analysis (RSA), the diffe rence between the RSA and the MAS is 0.12 degrees +/- 1.64 degrees. An accuracy with an error of 0.08 degrees +/- 1.15 degrees is determined by means of an angle gauge. Although a significant difference between the MAS and the goniometer (p = 0.04) is found around the X-axis (the ta; transverse plane), it is limited to <1 degrees. The MAS provides a n in-depth insight into the mechanism of the three-dimensional rotatio n at each vertebra in vivo. The backward inclination of the apical ver tebra (AV) and forward inclination of the upper-end vertebra (UEV) aro und the Y-axis (phi) results in a correction of the hypokyphosis shown by the Cobb angle in the sagittal plane. The clockwise rotation of th e UEV in the Z-axis (psi) leads to a reduction of the Cobb angle in th e frontal plane. Additionally, the MAS as an intraoperative alternativ e shows different results of the derotation maneuver by the Cotrel-Dub ousset instrumentation (CDI) compared with the computed tomography (CT ) scan. Our method gives more direct details of the derotation not inf luenced by patient posture, as observed in the CT scan.