Sidebending versus flexion-extension radiographs in lumbar spinal instability.

Flexion-extension radiography is accepted as an effective method for the diagnosis of lumbar spinal instability, but the usefulness of sidebending films is less well known. Flexion-extension and sidebending radiographs of 300 patients with clinically suspected lumbar spinal instability were analyzed retrospectively. Generally used criteria for lumbar spine instability were applied in the film analysis. Although flexion-extension and sidebending films were statistically significantly interrelated in the diagnosis of instability, intertechnique agreement remained poor. Flexion-extension films more frequently revealed signs of instability than sidebending films; 84 vs 50 patients. Signs of instability on sidebending films showed the best correlation with the findings of angular motion and posterior sliding instability on flexion-extension films. Sidebending films are complementary to flexion-extension films but are unlikely to be helpful on a routine basis.