An investigation of artefacts in lumbar discography

An artefact of lumbar discography which can confuse or negate delineation of the nucleus pulposus is presented. This artefact is the inadvertent injection of contrast medium into a cavity which is not the true nuclear cavity. A positive diagnosis cannot be made in this situation, normality has not been proven and, in particular, the presence of a protrusion of the nucleus through the annulus fibrosus may not have been demonstrated. Hypotheses are proposed to explain the occurrence of these artefactual injections.