Position and anatomical landmarks
The patient lies in the prone position on an X-ray permeable table with a pillow under the abdomen to flatten the lumbar lordosis. Provocative discography is performed in the operating theatre under strict sterile conditions. Thirty minutes before the intervention, the patient receives antibiotics (2 g cephazolin, i.v.). Many pain specialists also mix antibiotics within the intradiscal-injected contrast at a concentration of between 1 and 10 mg/ml (e.g., 3 mg/ml cephazolin). The administration of antibiotics to prevent discitis is disputed. Yet currently, international consensus exists to administer, prior to the procedure, antibiotics as part of the complete discography procedure. The most important condition for the prevention of discitis is the regulation of strict sterile techniques. The skin of the lower back and the gluteal region is thoroughly disinfected. The pain specialist and his assistant must wash their hands according to the hospital's local protocol, and must wear protective clothing (surgical caps, surgical jackets and sterile gloves). After the injection point has been marked, the patient is covered with a sterile drape. The same must be done with the C-arm. Due to the limited rotation of the C-arm, it must be located on the side of the patient where the needle is to be inserted.
The levels to be examined by discography are selected, based on a combination of medical history, physical examination and additional examinations. The symptomatic level and the two adjacent levels are always examined. One or two adjacent intervertebral discs can serve as control levels.
The least degenerated, or more likely asymptomatic, discs are studied first. The patient should be blinded to the disc level and should not be aware of the start of the disc stimulation. The patient should preferably be only lightly sedated during the procedure, but those on copious narcotics should be given a judicious dose so that their pain sensitivity is not exaggerated. The patient must be awake and able to report reliably during disc stimulation.
The C-arm is first positioned with the direction of the radiation beam parallel to the end plate of the lower vertebral plate of the disc. In the discs above L5-S1, the C-arm is then rotated ipsilaterally until the lateral aspect of the articular process overlies the axial middle of the disc to be punctured (Figure 1), and the disc height is at its maximum. In this projection, the needle can be inserted parallel to the direction of the radiation beam and brought into position (tunnel vision).
Figure 1. Starting point of the needle, assuming a maximum disc height, is such that the C-arm is rotated so that the facet column is between one-third and one-half of the vertebral body. As a result, the insertion point is directly lateral to the superior articular process (sap).
The target for puncturing the annulus fibrosis is the lateral-middle side of the disc, just lateral to the lateral border of the superior articular process (Figure 2). At the L5-S1 level, the iliac crest does not allow access to the disc using a down-the-beam approach. The C-arm is rotated until the lateral border of the superior articular process of S1 is positioned approximately 25% over the posterior-to-anterior distance of the vertebral body.
Figure 2. Needle positions for a perfect discography at levels L3/L4, L4/L5 and L5/S1.
For the positioning of the needles, a new needle is used for each disc to be examined. After anaesthetising the skin and underlying tissue, a one- or two-needle technique can be used to approach the disc. In a two-needle technique, a 20-G needle is advanced over the lateral border of the superior articular process. A 25-G hollow needle is then inserted through this needle and into the annulus fibrosis until it reaches the centre of the nucleus. The two-needle technique may help to reduce the incidence of discitis and allow the disc to be entered with small-diameter needles (e.g., 27-G), which may help to prevent the incidence of iatrogenic disc degeneration. The needle is carefully advanced to the needlepoint end position. Beyond the superior articular process, the needle passes through the intervertebral foramen in the vicinity of the ventral branch. In case of paraesthesia, the needle must be repositioned. A strong resistance is felt as the needle passes through the annulus fibrosis. The needle is pushed through the annulus fibrosis to the centre of the disc. The needle's progress is monitored in various projections, first in AP view and then in lateral view (Figure 3). Ideally, after placement, the needle is located in the middle of the nucleus of the disc nucleus, as seen in the AP view as well as in the lateral view.
Figure 3. Needle positions with tips in the middle of the discs at levels L3/L4, L4/L5 and L5/S1: AP view.
After verification of the correct needle position, the stylet is removed from the needle and the needle is connected to a contrast agent delivery system, which can measure the intradiscal pressure. The rate of infusion of the contrast agent should not exceed 0.05 ml/sec. This infusion rate reflects a static flow that corresponds with the distension pressure in the intervertebral disc. If a higher flow is used, false positive discographies can occur due to the resultant pressure peaks. These pressure peaks, due to vertebral end-plate compression and distention of the adjacent facet joint, often provoke pain. It is important that the disc expected to be the most painful is the last to be stimulated. The patient must not be able to see which disc is being stimulated.
If the painful disc is stimulated first, it is possible that the echo of that pain lasts long enough to make adequate stimulation at other levels no longer possible. When these conditions have been met, the stimulation can be started.
- The following parameters must be carefully monitored during injection of the contrast solution:
- Opening pressure (OP) is the pressure at which contrast is first visible in the disc.
- Provocation pressure is the pressure greater than the opening pressure at which complaints of pain arise.
- Peak pressure is the final pressure at the end of the procedure.
- Ideally, pressure, volume and provocation details are recorded at 0.5-ml increments, with additional notations being made for the above-mentioned events.
- Discitis is the most serious potential complication.