Application of image registration to measurement of intervertebral rotation in the lumbar spine

In this study, the precision and accuracy of a new method for measuring axial rotations of the lumbar vertebrae, which are thought to be increased in patients with degenerative spinal instability, were estimated. A standard image registration algorithm involving a user-selected center of rotation was adapted for this purpose. Accuracy was tested on a phantom containing a rotating lumbar vertebra. Calculated rotations were compared to the known values. Images were also obtained in subjects, using a tilting table that provided rotation between thorax and hips. For these measurements precision was estimated by varying the center of rotation. In the phantom the method had an accuracy of 0.2degrees. In the human subject measurements the precision was 0.60-1.5degrees. The method measured rotations of lumbar vertebrae with sufficient accuracy and precision to detect clinically significant differences in patients with back pain.