Introduction Controversy exists regarding the value of lumbar plain x-ray imaging for patients with low back pain with or without radicular pain (1,2,3).

Methods Plain film x-ray and CT imaging from thirty (30; 19M:11F) consecutive patients (aged 20–68 years; mean 42 years) presenting to a public hospital’s spinal pain clinic with low back pain +/− radicular pain, without a history suggesting ‘red flag’ pathology, was examined and measured to determine the incidence of retrolisthesis of L5 on S1 and any associated disc bulge/protrusion.

Results Sixteen of the thirty patients (53%) had retrolisthesis of L5 on S1 ranging from 2–9 mm; these patients had either intervertebral disc bulging or protrusion on CT examination ranging from 3–7 mm into the spinal canal. Fourteen patients (47%) without retrolisthesis (control group) did not show any retrolisthesis and the CT did not show any bulge/protrusion. On categorizing x-ray and CT pathology as being present or not, the well positioned ie. true lateral plain x-ray film revealed a sensitivity and specificity of 100% ([95% Conf. Int. = [89%–100%]) for bulge/protrusion in this preliminary study. On taking into account the numerical values of x-ray and CT, a significant correlation (p< 0.001) was found.

Discussion In this preliminary study, carefully positioned lateral lumbosacral x-ray films showing L5 on S1 retrolisthesis are highly suggestive of intervertebral disc bulge/protrusion, providing valuable guidance for consideration of lumbosacral CT of MRI examination that is likely to be contributory regarding such pathology.