Abstract:

BACKGROUND: Lumbar spondylolisthesis is commonly confirmed by using flexion and extension radiographs, and the severity is determined through slip distance and slip angle.
OBJECTIVE: To define and demonstrate the presence of “vertical instability” in lumbar spondylolisthesis, and to determine the most useful radiographic views for clinical purposes and analysis of the surgical strategy.
METHODS: Lateral and flexion extension radiographs of the lumbosacral spine in 37 patients with spondylolisthesis taken in standing and recumbent positions and under pelvic traction in the prone or supine positions were suitable for analysis. The changes in disc area, intervertebral kyphotic slip angle, and amount of anteroposterior shift (olisthesis) were measured from the radiographs using a computer digitizer.
RESULTS AND CONCLUSION: Maximum slip angle, maximum olisthesis, and minimum normalized disc area were found in patients under erect flexion. Conversely, prone traction and recumbent extension produced minimum slip angle, whereas the lowest anteroposterior shifts were seen in patients under prone and supine traction. Prone traction also resulted in a significantly larger normalized disc area than any other posture. The change in kyphotic slip angle between erect flexion and prone traction was correlated with the change in normalized olisthesis and disc area. Erect flexion and prone traction radiographs represent the extremes of subluxation and reduction of the olisthesis, respectively, and the change in olisthesis seen between these extremes is correlated with the change in disc area and the intervertebral slip angle. Vertical laxity of the affected functional spinal unit resulting from disc degeneration produces laxity in the ligaments and disc anulus, allowing olisthetic motion. Restoration of disc height in turn restores tension to the soft tissues around the disc and results in a spontaneous reduction of the subluxation. Restoration and maintenance of disc height with a spacer or interbody fusion therefore is recommended as a goal in the treatment of spondylolisthesis. When spondylolytic spondylolisthesis involves a posterior column deficiency, additional reconstruction of this column with posterior instrumentation is recommended.