Lumbar disc degeneration and segmental instability: a comparison of magnetic resonance images and plain radiographs of patients with low back pain.

We analyzed disc space height, angular displacement, tilting movement, and horizontal displacement in 109 patients with low back pain and/or sciatica, on plain radiographs of the lumbar spine. These parameters were compared with the grade of disc degeneration as evaluated by magnetic resonance imaging with the aim of studying lumbar segmental instability. Disc space height decreased in proportion to the grade of disc degeneration. Angular displacement was significantly less with severe disc degeneration, accompanied by a tendency to stabilization of the motion segment. Tilting movement and horizontal displacement did not correlate with the grade of disc degeneration. Lumbar segmental instability was recognized at all levels even in individuals who appeared to be normal or to have mild disc degeneration. The incidence of lumbar segmental instability at the L3-4 level was significantly higher in patients with normal discs or mild disc degeneration. At the L4-5 and L5-S levels it did not differ between different grades of disc degeneration.