The disk is preferentially approached from the side opposite the patient’s usual pain to avoid the patient mistaking discomfort secondary to needle placement with provoked pain secondary by disk stimulation. If the patient has central pain or the pain is equal bilaterally, or if there are other impeding technical factors, needle insertion from either side is fine.

The insertion point is marked on the skin. The distance between the opposite superior articular processes increases at the lower lumbar levels. At T12–L1, the needle insertion point is about 3–4 cm lateral to the midline; at L5–S1 it is approximately 6–7 cm lateral. At L5–S1, because of the iliac crest and increased interfacetal distance, ideal access to the disk may not be possible. The fluoroscope is therefore rotated only far enough to bring the superior articular process approximately 25 % of the distance between the anterior and posterior vertebral margins.

Prior to needle placement, a skin wheal is made with lidocaine 1 % (~1 cc) using a 25 gauge 1.5 in. needle. To anesthetize the needle track, one can use a 25 gauge 3.5 in. needle advanced under “tunnel vision,” i.e., parallel to the X-ray beam, to the level of the SAP. Exercise caution so as not to anesthetize the dorsal root ganglion within the foramen. Overenthusiastic anesthetization may obscure nerve root impalement and could potentially anesthetize the sinuvertebral and ramus communicans nerves, thus altering the evoked pain response during disk stimulation and creating a false-negative response.

A one- or two-needle technique may be used; however, most diskographers currently use a two-needle technique. Prior to the routine use of prophylactic antibiotics, Fraser et al. [24] reported a rate of diskitis with single non-styletted versus double needles of 2.7 % versus 0.7 %, respectively. Both the North American Spine Society and the International Spinal Injection Society recommend a two-needle approach [16, 19].

The two-needle technique utilizes a shorter, larger gauge introducer needle through which a longer, smaller gauge needle is advanced past the tip of the introducer needle into the targeted intervertebral disk, theoretically avoiding picking up any skin flora. The trend is to use a 20 gauge 3.5 in. introducer with the 25 gauge 6 in. disk puncture needle. The 25 gauge needle theoretically minimizes any trauma to the disk. Less experienced operators may start with the 18/22 gauge needle combination, particularly because the curve of the disk puncture needle is easier to maintain. The body habitus of the patient will dictate if longer needles are necessary, i.e., 5 in. introducer and an 8 in. disk puncture needle. A slight bend, opposite the bevel, is typically made at the tip of the disk puncture needle to allow the operator to “steer” the needle during extra- and intradiscal insertion [39–42]. At times a larger curve, at the distal third of the disk puncture needle, must be utilized to compensate for less than ideal anatomy or postsurgical changes.

The introducer needle is passed through the skin wheal at the skin puncture point, using a “down the beam” or “tunnel vision” technique on the oblique fluoroscopic view and is often felt to enter the foramen (Fig. 8.3). To protect the diskographer’s hand from radiation exposure, forceps may be used to grasp the introducing needle. To avoid potential neural injury, direct the needle into the region below the segmental nerve, just lateral to the superior articular process and above the end plate (Fig. 8.4). The disk puncture needle must travel under the segmental nerve coursing medial to lateral, and dorsal to ventral, to puncture the annulus fibrosus of the disk at the midpoint of the disk when seen in lateral and AP views. To minimize nerve trauma, one might consider use of a needle with a short, non-cutting bevel. However, a Quinke tip spinal needle is appropriate in that contact with the ventral ramus should be a rare occurrence if a modicum of care is utilized. Forward advancement is stopped at the approximate level of the SAP, although placement within the foramen, ventral to the intervertebral disk annulus, is acceptable. Use a lateral fluoroscopic view to check needle depth (Fig. 8.5).

The stylette is then removed from the introducer, and the longer, smaller gauge disk puncture needle is advanced slowly under real-time lateral fluoroscopy. The needle will be seen to transverse the intervertebral foramen; then, a firm but distinct change in resistance will be noted as the needle touches and punctures the annulus fibrosus. On the lateral view, the needle will typically contact the posterior disk margin 1–3 mm posterior to the vertebral margin. On AP projection, the diskogram needle ideally contacts the disk margin on a line drawn between the midpoints of the pedicles above and below (Fig. 8.6). The patient may experience a brief sharp “pinch” or sudden aching sensation when the needle pierces the innervated outer annulus fibrosus. In no case should one advance the introducer or diskogram needle medial to the inner pedicle margins before contacting the intervertebral disk. Using lateral fluoroscopy, the needle is then advanced to the center of the disk as seen on both lateral and AP projections (Figs. 8.7 and 8.8). AP and lateral projections are used to assure good needle placement, and spot films saved for documentation prior to injection of contrast.

If bony obstruction is encountered, the physician should use fluoroscopy to determine whether the needle has contacted the superior articular process or the vertebral body. If the SAP is contacted, the introducer needle can be withdrawn slightly and its trajectory modified. The introducer needle can be advanced to just over the lateral edge of the superior articular process or advanced to the dorsal margin of the disk. If the vertebral body is contacted, the introducer needle is withdrawn to a point where manipulation of the slightly bent disk puncture needle can compensate for the nonoptimal placement of the introducer needle.

If the patient experiences any radicular pain or dysesthesia during needle advancement, insertion of the needle must halt. The ventral ramus may be encountered because it crosses the posterior-lateral aspect of the disk in close proximity to the disk entry site. In such a case, the needle is partially withdrawn to alter its course and redirected toward the disk. A slight bend in the needle tip facilitates small directional adjustments. Typically, redirection of the needle more medially and caudally will avoid the segmental nerve. If greater direction changes are needed, withdraw and redirect the introducer needle as well.

The above technique can be utilized for disk puncture in greater than 95 % of lumbar disk levels; however, occasionally, due to anatomical variations (i.e., overriding iliac crest, osteophytes) or postsurgical changes (i.e., posterior intertransverse fusion mass or fusion hardware), variations in the procedure must be utilized. A detailed description of the myriad modifications with which a diskographer might be faced is beyond the scope of this chapter; however, most involve either a more lateral or more medial needle insertion with the disk puncture needle bent or curved to varying degrees. Rarely, the posterior interpedicular, transdural, approach must be used for disk puncture. This technique increases the chance for morbidity since the dura is punctured twice. Risks and benefits of this technique must be weighed. At the L2–L3 level and above, the posterior approach should never be used due to the real risk of impaling the spinal cord.

Disk puncture at L5–S1 can be technically more challenging than the L1–L4 levels when due to the increased inter-facet distance and the proximity of the iliac crest which obscures direct access to the disk nucleus. When optimal obliquity is not possible due to bone, less rotation is required. After the L5–S1 intervertebral disk has been identified and the superior end plate of the S1 vertebral body is aligned with the X-ray beam, the image intensifier is ipsilaterally obliqued until the ilium or sacral ala obscures the disk target. Counter rotation then is used to evidence a clear path to the lateral disk access. At this point, the S1 superior articular process (SAP) may be only 25 % of the distance between lateral vertebral borders. Less than 2 cm of the L5–S1 disk is visualized between the superior articular process of S1 and the sacral ala (Fig. 8.9). Unlike the direct approach at the levels above, a slight to marked curve or “hockey-stick” bend is required for the diskogram needle insertion at this level. Under the oblique fluoroscopic view, the introducer needle is advanced toward the bony notch between the S1 superior articular process (SAP) and sacral ala. The needle tip should be immediately adjacent to the anterolateral aspect of the S1 SAP (Fig. 8.9). Next, sterile gauze is used to curve the distal 2–3 cm of the diskogram needle into a smooth arc in the direction opposite the bevel (Fig. 8.10). The degree of curve is operator dependent, based on the amount of medial deflection required to reach the center of the disk. Under a live lateral fluoroscopic view, the curved diskogram needle is advanced through the guide needle until the tip emerges and is felt to gain purchase in the outer annulus. The needle is then directed in a medial and slightly posterior course around the SAP to stay within the safe region (Fig. 8.4). For some diskographers, the 18/22 gauge needle combination may be easier to direct versus the 20/25 gauge needle combination used at upper levels. Obese or muscular patients may require longer needles. Once the diskogram needle reaches the annulus fibrosus, its position is checked in both AP and lateral views. In the lateral view, the needle should contact the disk 2–3 mm posterior to the vertebral margin (Fig. 8.9b), and in the AP view, the needle should ideally be on a line bisecting the midpoint of the L5 and S1 pedicles. The needle course must be closely monitored; if the needle does not curve sufficiently in the medial direction, it will not reach the center of the disk; moreover, it may strike the ventral ramus. If the needle does not track medially and posteriorly, it must be removed and its curvature accentuated. Once the disk puncture needle is within the outer annulus and is slowly advanced, the introducer needle can be withdrawn to reinstitute and accentuate the bend on the disk puncture needle facilitating medial deviation. As mentioned previously, if the needle contacts bone, determine whether the superior articular process or the vertebral body has been encountered and make appropriate adjustments. Ideally, the final needle position is the center of the disk; however, there is leeway. In severely degenerated disks, the needle position is not as crucial because the contrast spreads throughout the disk due to loss of the intrinsic disks architectural integrity. Ideally, the needle should be within 4–5 mm of the disk center on AP and lateral fluoroscopy.