[Technic of extradural diskography]

Extra-dural discography is an ambulatory investigation. The exact technique is based upon three principles: a) the patient is in a 3/4 position on the table; b) follow the direction of the actual central ray or of a correction applied to it when the disc is impacted. This correction is made using a ruler, abacus and goniometer placed on the support of the tube; c) use of a range of special needles, certain of which have been curved at the time of manufacture. Interpretation of the results of a series of 121 cases of sciatica treated surgically after discography has confirmed the reliability of the method as shown by operative findings in particular when discography has shown a protrusion of 5 mm or more (94% of results showing agreement). Amongst degenerated discs, the distinction must be drawn between those without a protrusion and those with, hence the value of measuring the raised area caused by the contrast medium in the epidural space. Finally, the existence of an epidural leak is compatible with all the types of lesion seen.