Rotational hypermobility of disc wedging using kinematic CT: preliminary study to investigate the instability of discs in degenerated scoliosis in the lumbar spine

The number of patients showing lumbar degenerative scoliosis, including disc wedging, has increased, and examination of the mechanism of spinal nerve compression due to lateral and rotational mobility of the lumbar spine is necessary. Thirty-two patients with L4–L5 disc wedging but without antero- or retrospondylolisthesis and ten age-matched controls were examined. The angle of disc wedging and change in the angle between left and right bending were evaluated by anterior–posterior X-ray images of patients while they were in a standing position. The degree of disc degeneration and existence of vacuum phenomena were evaluated at the L4–L5 discs. Rotational mobility between maximal right and left rotation was examined by computed tomography (CT). Rotational mobility was measured using the spinal transverse processes of L4 and L5. The relationship between these factors was statistically evaluated using multivariate analysis and Spearman’s correlation test. There was a significant increase in the average rotational mobility of the L4–L5 disc-wedging group. In the L4–L5 disc-wedging group, the increased angle of disc wedging and change in the angle between left and right bending correlated with increased rotational mobility. The degree of disc degeneration did not affect rotational mobility. However, existence of vacuum phenomena increased the rotational mobility of the L4–L5 disc-wedging group. This is the first study to evaluate the rotational hypermobility of L4–L5 disc wedging in patients without antero- or retrospondylolisthesis using kinematic CT. Increases in the wedging angle and abnormal instability of lateral bending correlated with increased rotational mobility. For surgical planning of degenerative L4–L5 disc wedging, it is important to consider rotational hypermobility using kinematic CT or X-ray imaging findings of lateral bending.