Importance of correlating static and dynamic imaging studies in diagnosing degenerative lumbar spondylolisthesis.

Degenerative spondylolisthesis in the lumbar spine is due to long-standing segmental instability. A standing plain radiograph is commonly the only imaging study needed to establish the diagnosis. Translatory motion in spondylolisthesis is traditionally assessed with lateral flexion and extension radiographs. These dynamic studies often demonstrate a decrease in the slip percentage between the vertebral segments with extension and an increase with forward flexion. Some low-grade spondylolisthetic deformities reduce anatomically on the operating table after the administration of an anesthetic. We encountered one case in which there was complete reduction of an L4-5 grade I degenerative spondylolisthesis with positioning of a non-anesthetized patient in the supine position during a lumbosacral magnetic resonance imaging (MRI) scan. The patient's condition was originally misdiagnosed, as the spondylolisthesis was not identified on recumbent plain radiographs or on lumbosacral MRI. This case stresses the importance of correlating static and dynamic imaging studies in developing a treatment plan for patients with degenerative spondylolisthesis.