Puncture of T12–L1 through L4–L5 intervertebral discs

In the double-needle technique, a styletted 25-gauge, 6-inch needle is placed into each disc through a 20-gauge 3.5-inch introducer needle under fluoroscopic guidance. To protect the discographer’s hand from radiation exposure, forceps may be used to grasp the introducing needle. The introducer needle is advanced parallel to the fluoroscopic beam using an oblique fluoroscope view (Fig. 25.3).

Fig. 25.3 The introducing needle should proceed parallel to the fluoroscopic beam using an oblique fluoroscope view.

A slight ‘hockey-stick’ bend at the end of the introducer needle can improve navigation. If bony obstruction is encountered, the physician should confirm whether the needle has contacted the superior articular process or the vertebral body. If necessary, the needle may be slightly withdrawn and its trajectory modified. The introducer needle can be either advanced just over the lateral edge of the superior articular process or advanced to the margin of the disc. At the L5–S1 level, advancement may proceed just over the lateral edge of the superior articular process. When the introducer or discogram needle contacts the disc margin, the ideal position in the AP projection is on a line drawn between the midpoints of the pedicles above and below (Fig. 25.4A).

Fig. 25.4 The ideal position of needle when the needle contacts the disc is on the line between midpoint of pedicles at AP (A) and posterior vertebral margin at lateral view (B) (P, pedicle).

In no case should one advance the introducer or discogram needle medial to the inner pedicle margins before contacting the intervertebral disc. In the lateral view the needle should contact the disc between the posterior vertebral margins (Fig. 25.4B).

After confirming introducer needle position with a lateral view, a 25-gauge, 6-inch needle is advanced into the center of the disc through the introducing needle while monitoring by lateral view. A slight ‘hockey-stick’ bend on the end of the discogram needle facilitates navigation. When the needle contacts the disc, position should be checked using AP and lateral views. Contact with the anulus fibrosus is characterized by the perception of firm but resilient resistance, and frequently the patient experiences a momentary, sharp, or sudden aching sensation in the back or the buttock. The needle is then advanced to the center of the disc. Needle position must be monitored and checked by both AP and lateral imaging.

L5–S1 intervertebral disc

Due to increased facetal width and the presence of the iliac crest diacrest, puncture of the lumbosacral disc is more challenging. Instead of a direct lateral approach, once the introducer needle is advanced to the anterior border of the superior articular process of S1, a slight curve or ‘hockey-stick’ bend is needed to advance the discogram needle in a medial and slightly posterior direction around the SAP to contact the disc just anterior to the vertebral margin as viewed in the lateral fluoroscopy projection. Less experienced operators may find an 18/23-gauge needle combination easier to direct than the 20/25-gauge combination used for upper levels. Longer needle combinations may be required in muscular or obese patients. The fluoroscopy tube is rotated until about 1–2 cm of the L5–S1 disc is visualized between the superior articular process of S1 and the sacral ala (Fig. 25.2).

Using the oblique fluoroscopic view, the guide needle is introduced toward the bony notch between the sacral ala and superior articular process of S1 until the needle tip lies immediately adjacent to the anterolateral aspect of the superior articular process of the sacrum (Fig. 25.5A). The needle tip should not be handled directly, but should be wrapped in sterile gauze. The distal 2–3 cm of the needle should be bent in a direction opposite the bevel. The degree of curve is determined by the operator on the basis of how much deflection is required in the patient at hand for the needle to approach the target disc center. In a lateral fluoroscopic projection, the 25-gauge discogram needle is passed through the guide needle while the guide needle is held firmly in position. The inner needle is advanced until the tip emerges from the guide needle. The inner needle is advanced under direct fluoroscopic vision. As it emerges, the guide needle is retracted slightly (Fig. 25.5A). This unsheathes the procedure needle, which should be turned so that the curve or bend bows the introducer needle in a medial and posterior direction through the safe triangle. Once the needle encounters the anulus fibrosus, its position is checked and confirmed in both AP and lateral fluoroscopy views. In the lateral view the needle should contact the disc 2–3 mm anterior to the vertebral margin (Fig. 25.5B) and in the AP view the needle should ideally be on a line bisecting the midpoint of the L5 and S1 pedicles.

Fig. 25.5 (A) Oblique view of L5–S1 discography. The inner needle is advanced slightly under direct fluoroscopic vision, and the guide needle is simultaneously retracted slightly. (B) Lateral view. The inner needle should contact the disc 2–3 mm anterior to the vertebral margin.

If the inner needle fails to curve medially it will not pass toward the center of the disc, and may strike the ventral ramus. As a result, the needle course must be monitored. If the needle fails to track medially and posteriorly, the needle should be removed and its curvature accentuated. Should the procedure needle meet with bony obstruction, the fluoroscope should be turned to determine whether the superior articular process or the vertebral body has been encountered. If the vertebral body has been encountered, the course of the needle can be corrected by withdrawing it slightly and rotating the needle appropriately. If the needle is blocked by the superior articular process, the inner needle is retracted into the guide needle and the pair are advanced to the lateral edge of the S1 superior articular process. The inner needle may then be directed toward the disc as described above. The ideal final needle position is in the disc center; however, there is leeway. In severely degenerated discs the needle position is not as critical, since contrast medium will spread throughout the disc. Ideally, the needle should be within 4–5 mm of the center on AP and lateral fluoroscopy.

Provocation

Once the needle tip has been properly placed in the center of the nucleus pulposus, nonionic contrast medium mixed with antibiotic is injected into each disc at slow velocity using a controlled injection syringe with digital pressure readout. The total volume injected should probably be limited to 3.5 mL. Although a few severely degenerated discs will accept more volume, the incidence of false-positive pain responses may increase. If one cannot achieve 50 psi above opening pressure at 3.5 mL due to the degree of disc degeneration or a leak through the endplates or anulus, a dynamic pressure of 50 psi above opening can usually be achieved by more rapid injection. In general, however, the media should be injected as slowly as possible. Higher injection speeds may cause rapid pressure elevations leading to increased pressure differences between the nucleus pulposus and manometer and between the dynamic and static pressures. At 0.05 mL/sec (one revolution of the Merit monometer) the difference between static and dynamic pressures is minimal. The intrinsic disc pressure is the pressure required to start the flow of contrast medium into the nucleus (opening pressure) resulting from osmotic forces within the disc resisted by anulus tension and the tension of the anterior and posterior longitudinal ligaments. Typical opening pressures are 5–25 psi, depending on the degree of nuclear degeneration. An opening pressure >30 psi usually indicates that the needle tip is within the inner anulus. In this case, the needle tip should be repositioned.

The disc is slowly pressurized by injecting 0.5 mL increments through a syringe attached to a pressure measuring device. At each 0.5 mL increment, the injection pressure, location of contrast medium, and any pain response are recorded. At a slow injection speed, the dynamic pressure more closely reflects the real intradiscal pressure than the static pressure taken without pressure applied to the injecting syringe. Injection continues until one of the following end points is reached: subject pain = 6/10, intradiscal pressure >50 psi above opening in a disc with a grade 3 annular tear or 80–100 psi in a normal-appearing nucleogram, or a total of 3.5 mL of contrast medium has been injected.

Imaging

The appearance of the normal nucleus following the injection of contrast medium is unmistakable: the contrast medium assumes a lobular pattern or a bilobed ‘hamburger’ pattern (Fig. 25.6A). A variety of patterns may occur in abnormal discs.⁹ Contrast medium may extend into radial fissures of various lengths but remain contained within the disc (Fig. 25.6B), or it may escape into the epidural spaces through a torn anulus (Fig. 25.6A). In some cases (Fig. 25.6C), the contrast medium may escape through a defect in the vertebral endplate.³ However, none of these patterns alone is indicative of whether the disc is painful; that can be ascertained only by the patient’s subjective response to disc injection.

Fig. 25.6 The appearance of the nucleus following the injection of contrast media. (A) The contrast medium assumes either a lobular pattern or a bilobed (‘hamburger’) pattern (black arrowhead) as a normal nucleogram. Contrast medium escaped into the epidural space through a radial fissure at L5–S1 level (white arrow). (B) Contrast medium extended into radial fissures (arrow) but remain contained within the disc. (C) The contrast medium escaped through a defect in the vertebral end plate (white arrowheads).

Immediately after discography, CT–discography may be performed to define fissures extending to the outer third of the anulus and extending circumferentially within the anulus fibrosus. Radial annular tears can be found by discography, but only the postdiscogram CT axial view clearly shows the location and size of fissures within the anulus fibrosus.³ Sachs et al.¹⁰ developed the Dallas discogram scale, in which annular disruption is graded on a 4-point scale. Grade 0 describes contrast medium contained wholly within a regular nucleus pulposus. Grades 1 to 3 describe the extension of contrast medium along radial fissures into the inner third, middle third, and outer third of the anulus fibrosus, respectively. Aprill and Bogduk¹¹ proposed a modified Dallas description scale which includes grade 4, distinguished from grade 3 by the spread of contrast medium circumferentially within the substance of the anulus fibrosus and subtending a >30° arc at the disc center.

Interpretation

The most important information obtained from discography is whether the patient’s pain is reproduced. There is no alternative or superior means of determining if a disc is the source of a patient’s pain. Conceptually, discography is an extension of clinical examination, tantamount to palpating for tenderness. It is only the inaccessibility of a disc to palpation that requires the use of needles. In this regard, it is critical that the criteria for a painful disc be rigorously satisfied. Internal control observations are mandatory: a disc cannot be deemed the source of a patient’s pain if stimulating other discs or other structures in the same region reproduce similar pain.

Assessing patient response to discography requires measuring the pain reproduced by injection. Pain may be characterized by three components: intensity, location, and character. If the location and character of pain provoked during discography are similar to or the same as the patient’s clinical symptoms, the criteria for concordant pain are satisfied. The intensity of pain is measured by the patient (e.g., by using a numerical rating scale) and by observed pain behaviors. The intensity of provoked pain, however, is dependent on stimulus intensity. In simple terms, the harder one pushes on the syringe the more likely the disc is to hurt. By measuring intradiscal pressures, stimulus intensity can be quantified and standardized, permitting more reliable comparisons among patients and discographers. While injection pressures may be manually estimated, use of a controlled inflation syringe with digital pressure readout is more precise.

Adding pressure monitoring to provocative discography improves interobserver reliability and, as a result, reproducibility. A positive discogram requires an abnormal disc, pain response =6/10 (numeric rating scale; NRS), pressure level =50 psi, pain described by the participant as ‘familiar,’ and at least one negative control disc. One must, however, be aware that transient pain is often provoked when fissures are suddenly opened. In most cases, such pain should not be used as evidence of a true-positive response unless pain >6/10 is sustained for more than 30 seconds. Most experienced discographers will perform a confirmatory re-pressurization once a suspected positive response is provoked. If re-pressurization does not again provoke significant concordant pain at 50 psi or less above opening pressure, then the initial response will remain indeterminate. These criteria for positive response were reconfirmed in a study performed in 13 normal asymptomatic volunteers.^11a,11b When the operational criteria for discography were set to pressure =50 psi and evoked pain intensity >4, the expected false-positive rate was <10%. However, a false-positive rate of zero could be secured either if the pain score was held at 4 and the injection pressure lowered to 20 psi, or if the pressure was held at 50 psi and the required pain score was raised to 6. To increase discography specificity, local anesthetic may be injected into the positive disc in an effort to obtain prolonged relief of pain from that disc (analgesic discography). In a preliminary study investigating the reliability of analgesic discography, 78% of patients showed significantly prolonged pain relief after local anesthetic injection. Those patients underwent fusion surgery and were followed to observe surgical outcome (T. Alamin, personal communication, 2004).

In addition to these criteria for positive discography, disc anulus sensitivity may also be graded. Using the protocol of Derby et al.,¹² four disc categories may be defined: (1) chemical discs, which provoke pain at 15 psi above opening pressure, (2) mechanical discs, which provoke pain at pressures between standing and lying, or 15–50 psi above opening pressure, (3) indeterminate discs, which provoke pain at 51–90 psi above opening pressure, and (4) normal discs, with no pain provocation. If a disc is painful at >50 psi, the response cannot be considered clinically significant, since it is difficult to distinguish from the effect of mechanically stimulating a normal or subclinically symptomatic disc.¹³ Excessive stimulation involving pressures >50 psi above opening pressure and uncontrolled, high injection speeds increase false-positive responses.