A noninvasive, three-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 each vertebra. Objectives. To develop a method of performing three-dimensional, noninvasive motion analysis of the spine using computed tomography data. Summary of Background Data. The concept of using principal axes of the moment of inertia tensor to measure the orientation and position of a rigid body has been applied to the wrist and subtalar joints, but has not yet been applied to the spine. Methods. Scans were taken of two isolated vertebrae in various known positions. Centroids, area, moments, and product of inertia of each scan were determined using a commercial program. Custom software combined data using the parallel axis theorem to give three-dimensional data for each vertebra. Changes in the centroid and principal axes were used to calculate translation and rotation? respectively. Results. The system accuracy was within 1.0 degrees in rotation and 1.0 mm in translation. Some errors occurred in minor motions when a smaller number of scans were used System resolution was 0.43 mm. Conclusions. A system has been developed capable 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 studies will be necessary to apply this system in vivo.