A NONINVASIVE, 3-DIMENSIONAL SPINAL MOTION ANALYSIS METHOD

Study Design. A three-dimensional, noninvasive motion analysis method was developed by monitoring the orientation of the principal axes of e ach vertebra. Objectives. To develop a method of performing three-dime nsional, noninvasive motion analysis of the spine using computed tomog raphy data. Summary of Background Data. The concept of using principal axes of the moment of inertia tensor to measure the orientation and p osition of a rigid body has been applied to the wrist and subtalar joi nts, but has not yet been applied to the spine. Methods. Scans were ta ken of two isolated vertebrae in various known positions. Centroids, a rea, moments, and product of inertia of each scan were determined usin g a commercial program. Custom software combined data using the parall el axis theorem to give three-dimensional data for each vertebra. Chan ges in the centroid and principal axes were used to calculate translat ion and rotation? respectively. Results. The system accuracy was withi n 1.0 degrees in rotation and 1.0 mm in translation. Some errors occur red in minor motions when a smaller number of scans were used System r esolution was 0.43 mm. Conclusions. A system has been developed capabl e 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 studie s will be necessary to apply this system in vivo.