Stereo radiography of lumbar spine motion.

The technique of Biplanar Radiography for the computer analysis of orthogonal radiographs of the human spine enables the calculation of three-dimensional coordinates for anatomical landmarks on the vertebrae. Three-dimensional intervertebral movements are deduced from the changes in the relative orientations of the vertebrae as a subject moves from one position to another. The three-dimensional coordinates of the anatomical landmarks on the vertebrae were found to have an RMS error of less than 1 mm. The RMS errors for translational movements were less than 2 mm and for rotations were less than 1.5 degrees. This study of normal subjects has defined the ranges of voluntary flexion and extension, axial rotation, and lateral bending in the lumbar spines of young males. The range of flexion plus extension at each lumbar intervertebral joint is approximately 14 degrees with the L4/5 level being slightly more mobile than the others. There are approximately 2 degrees of axial rotation at each joint with L3/4 and L4/5 being slightly more mobile. Lateral bending of approximately 10 degrees occurs at the upper three levels while there is significantly less movement of 6 degrees and 3 degrees at L4/5 and L5/S1 respectively. In flexion and extension accompanying axial rotation of 2 degrees or more and lateral bending of 3 degrees or more occurred rarely and any larger accompanying rotation at an intervertebral joint should be considered abnormal. During twisting and side bending axial rotation to the right is accompanied by lateral bending to the left and vice versa at the three upper levels. At L5/S1 axial rotation and lateral bending generally accompany each other in the same direction while L4/5 is a transitional level. During lateral bending there is also generally extension at the upper levels and flexion at L5/S1. The measurement in vivo of the accompanying rotations in the other planes has demonstrated that there is no simple mechanical coupling of the rotations. Finally, this study has provided a base line of normal movements to which the movements seen in pathological conditions can be compared.