Instability Missed by Flexion-Extension Radiographs Subsequently Identified by Alternate Imaging in L4–L5 Lumbar Degenerative Spondylolisthesis

Our study provides evidence that flexion and extension radiographs underreport the dynamic extent of LDS and therefore should not be solely relied upon to ascertain instability. These findings have implications for how instability should be established and the extent of surgery that is indicated.