Epidural Corticosteroid Injections: Technical Considerations - Part B
Technical Considerations Continued ...
Fig 3. Interlaminar cervical epidural blocks should only be performed by experienced injectionists. It is important to be absolutely confident as to the depth of needle penetration. Injection should rarely be undertaken above the C7-T1 level. At higher levels, a catheter can be advanced.
Figures a-c demonstrate the steps in performing an epidural injection using a catheter technique. The radiographs show a 17 gauge Tuohy needle advanced through the T1-2 interspace for the purpose of advancing the catheter to the C5 segment. The T1-2 interspace is often chosen because the epidural space is somewhat deeper at this level than at the C7-T1. The skin and subcutaneous fascia to the lamina can be first infiltrated with local anesthetic under direct fluoroscopic vision. Figure 3a shows the Tuohy needle first advanced to the upper lamina of T2. Once the lamina is contacted, it can be walked off 3-5 millimeters until the ligamentum flavum is contacted. Once contacted, the needle is advanced through the ligamentum flavum using "loss of resistance to fluid" technique. Figure 3b shows the Tuohy needle in the epidural space, 1 millimeter to the left of the midline at the T1-2 level. The catheter can then be advanced to the desired level. In this case, the catheter is advanced to the mid-body of T4 (Figure 3c). .05 ml of non-ionic contrast is injected and shows an epidural pattern. It is important to note that contrast stays within the epidural space, ruling out intravascular or subarachnoid injection.
Translaminar injections, sometimes referred to as paramedian translaminar epidural (PLE), are placed dorsally (posteriorly) by passing a needle through an interlaminar space, preferably just lateral to the interspinous ligament (3, 20). This needle must then penetrate the ligamentum flavum prior to entering the epidural space but just superficial to the underlying dural sac. (Fig 3.) Significant dexterity and manual feel for a "loss of resistance" with a special syringe is required in this technique. Final placement of injectate is dependent on diffusion to get to the ventral target tissue with this technique. (Fig 4.)
Figure 4(a) The AP view demonstrates excellent multi-segmental bilateral spread of contrast. However, the lateral view image (4b), taken one minute after injection, demonstrates the primary difficulty with interlaminar epidural injection procedures. (In this case, 1 cc of 4% Xylocaine, 1 cc of contrast, and 1.5 cc of Celestone were injected.) Most of the injectate remains contained in the dorsal compartment. Unfortunately, this is not the site of primary pathology although at the C5-6 and C6-7 levels there has been some ventral spread to the area of pathology. On the other hand, selective epidural blocks apply the local anesthetic and corticosteroid much more precisely to the area of pathology (4c).