Influence of spinal posture on abnormalities demonstrated by lumbar myelography

During spinal movements the dural end sac undergoes displacement and deformation, chiefly because of bulging of intervertebral disks and flaval ligaments in lumbar extension. Under normal circumstances these dural changes of form do not lead to clinical symptoms. However, in patients with spinal stenosis radiologic signs may be accentuated in lumbar extension. These tend to disappear in flexion. This implies that examination techniques performed in extension (prone lumbar myelography) tend to enhance abnormalities, while techniques in which the spine is more or less flexed (epidural phlebography, computed tomography) tend to mask them. In addition, there may be discrepancy between the picture during surgery (usually in lumbar flexion) and the situation in which a patient experiences symptoms (usually in lumbar extension in spinal stenosis).