Novel Method for Precise Multilevel Injection Through a Single Skin Puncture: Entry over Target Fluoroscopic Technique

Dear Editor, We present a novel method designed to reach multiple targets through a single skin puncture while maintaining a co-axial “gun barrel” fluoroscopic approach. Many interventional pain procedures are performed with subcutaneous infiltration of local anesthetic at the site of needle entry. Skin anesthetization is important for patient comfort, yet it possibly increases the false positive rate of diagnostic nerve blocks such as medial branch blocks (MBBs) and lateral branch blocks (LBBs), used for lumbar facetogenic and sacroiliac joint pain, respectively [1]. These procedures often involve multiple levels and multiple skin punctures. Stojanovic et al. [2] proposed an alternative solution that minimizes the number of skin punctures. In the “single-needle” approach, the needle is withdrawn close to the skin surface and repositioned for the next block. The C-arm is maintained in the same anterior/posterior view. Although this method successfully obviates the need for additional skin punctures, it becomes more challenging when the needle is driven nonaxially to a distant target where the depth and angle are uncertain and estimated. Some practitioners may be more comfortable with the co-axial approach and prefer the security of bony landmarks for safety reasons. Additionally, misjudgment of depth and angle in the single-needle approach could theoretically lead to increased procedure time or needle entry into unintended targets. Therefore, we propose a modified version of the single-needle method that would allow co-axial approach for multiple targets with systematic fluoroscopic reorientation of the entry site over the target zone. The entry over target (ET) technique can be used for any procedure where minimizing the number of skin puncture sites is desired and multiple targets are within reach. We have found it to be particularly useful in lumbar medial branch blocks, but it could also be used for sacral lateral branch blocks and cervical medial branch blocks. This potentially reduces the number of skin punctures from two to three down to one. Abuzayed et al. studied morphometrics of the adult spine [3]. They found that the lumbar spine measured 26.12 mm and 9.14 mm, averaging 35.26 between medial branches. Based on these measurements, using a standard 89 mm spinal needle, a single skin puncture site should allow access to adjacent lumbar levels. The fluoroscopic images in Figure 1, A–C, demonstrate a left-sided L4 and subsequent L3 medial branch block using the ET technique. With sufficient needle length, the process can be repeated for subsequent targets (L5 dorsal ramus). (A) Central location of L4 MBB chosen as initial target. Radiopaque marker placed over skin surface to create radiographic reference point. (B) C-arm repositioned to superimpose reference point over location of L3 MBB. (C) Radiopaque marker removed. Primary needle is withdrawn to just beneath the skin surface and driven co-axially to new target. Target 1: L4 medial branch Drive needle to desired target in a co-axial “gun barrel” view. Needle is retained in place while stylet is re-inserted. Create a radiographic reference point (Figure 1A). Place a second needle or radiopaque marker horizontally on the patient’s skin surface, crossing the primary needle at its skin insertion site. This forms a radiographic reference point correlating to the insertion site at the skin surface. This is the point where the primary needle will be withdrawn close to the skin surface and, while remaining subcutaneous, redirected to the next target. Target 2: L3 medial branch (Figure 1B) Superimpose reference point over new target by repositioning C-arm until the crossed needles are lying directly over the target. In essence, this uses the fluoroscopy beam to create a linear vector through the skin puncture to the target. Drive needle co-axially to second target (Figure 1C). Second needle or radiopaque marker is removed from field. Primary block needle is withdrawn until the tip is just beneath the skin. While still in subcutaneous tissue, needle is redirected in a co-axial “gun barrel” view to the new target location. The cardinal principal for every injection is that the target must first and foremost be visualized. Therefore, one limitation when using the ET technique is that views may not be optimal for every target, nor is every target always accessible from the starting point. Parallax must be accounted for as targets become less optimal in order to continually achieve co-axial views. Correlation with anterior/posterior and lateral fluoroscopic views may still be needed (although these are potentially needed with conventional techniques). Conversely, literature has shown that even small amounts of volume such as 0.5 mL will spread and likely reach targeted MB several millimeters away in the event that the needle tip has strayed from the intended target somewhat [1]. A second limitation is that this technique may be difficult in patients with a larger body habitus. Longer needles may be difficult to drive to distant targets while standard 3.5” needles may not cover the necessary distance. However, using the reference measurements provided above and determining depth of needle insertion to first target, the distance to the next target can be approximated as a geometric hypotenuse. From a practical standpoint, if the first target requires almost all of the needle length, the ET technique may not be feasible with the same needle. Finally, it is possible that while skin puncture pain is reduced, there may be increased pain from other sources. With more distant levels, the needle will take a longer pass through soft tissue structures before landing on the spine. Skin punctures are an important source of patient anxiety and discomfort during interventional procedures. The ET technique augments safe and precise alignment of multiple radiographic targets from a single entry site while maximizing efficiency and patient comfort. It is not a replacement for proper anatomic knowledge and confirmatory fluoroscopic views for interventional pain procedures.