Movements of the lumbar spine measured by three-dimensional X-ray analysis.

Techniques for the calculation from biplanar radiographs of the three-dimensional coordinates of anatomical landmarks on human lumbar vertebrae, and of the movements in three dimensions of the vertebrae between different positions of the spine are presented. The calculation of three-dimensional coordinates uses a calibration procedure based on direct linear transformation. Coordinate systems are used to define the orientations of each vertebra, and movements are derived from coordinate transformations between neighbouring vertebrae. The root mean square error in determining the absolute locations of anatomical landmarks was found to be less than 1 mm. For the movements of one vertebra relative to its neighbour the root mean square errors for translations were less than 2 mm and for rotations were less than 1.5 degrees. The system has been used to assess patients after spinal fusions and is currently being used in the diagnosis and assessment of patients with specific pathologies.