Prospective clinical study.

To determine the optimal posture for instability evaluation using flexion–extension X-ray imaging in patients with lumbar spondylolisthesis.

Currently, flexion–extension X-ray imaging is the most practical approach for the evaluation of lumbar instability. In flexion–extension X-ray imaging, achievement of the greatest segmental motion with flexion–extension movement is necessary. However, to our knowledge, currently, there is no standardized posture for determining lumbar instability.

Twenty-three individuals with lumbar spondylosis related to the fourth vertebra underwent flexion–extension X-ray imaging in different postures (standing, sitting, and lateral decubitus positions), lumbar magnetic resonance imaging (MRI), and low back pain Visual Analog Scale (VAS) evaluation on the same day. Intervertebral angle, percent slippage, and intervertebral disc area ratio for different postures during flexion and extension were compared using Tukey’s method. The effect of low back pain and the association between MRI facet effusion and these measurements were investigated according to posture.

The percent slippage during extension (p=0.036), change in the percent slippage between flexion and extension (p=0.004), and change in the intervertebral angle (p=0.042) were significantly different between the sitting and lateral decubitus positions. There were also significant differences between the standing and lateral decubitus positions in the change in intervertebral angle (p=0.010). In patients with VAS score <40, there were significant differences in the intervertebral angle (p=0.011) between the standing and lateral decubitus positions, percent slippage (p=0.048), and intervertebral disk ratio (p=0.008) between the sitting and lateral decubitus positions. We found no relationship between MRI facet effusion and posture in terms of instability.

In this study, intervertebral instability was best evaluated in the lateral decubitus position when using flexion–extension X-ray imaging for patients with fourth lumbar vertebral spondylolisthesis.