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The recognition of needle entry into an epidural space is a pivotal moment in cervical, thoracic, or lumbar epidural injections. Its significance cannot be overestimated. Regardless of how experienced you are, realizing that you are approaching an epidural space makes your heart beat faster. The safety of the procedure and its success rate depends upon proper and reliable identification of the needle entering into the epidural space. Recent advances in our understanding of fluoroscopic guidance allow pain practitioners to safely place the needle close to the ventral interlaminar line (VILL) [1–4]. However, recognition of the needle exiting the ligamentum flavum and entering into the epidural space was until now performed with the art of the loss of resistance technique (LORT). To rely upon LORT, a practitioner has to master his tactile sensation of change in resistance to the level of an expert. The contrast spread technique (CST) , on the contrary, depends upon the knowledge and ability to utilize fluoroscopy to recognize needle depth. We use various fluoroscopic views, and our understanding of clinical anatomy, to create a three-dimensional visualization of the needle tip inside the human body, and to answer the following questions: how close is the needle tip to the epidural space, and how far is it from the midline?
Using CST brought me to two paradoxical findings. There may be no need for the LOR syringe, and there may be no need for an epidural needle. My first finding is understandable, as CST does not rely on tactile loss of resistance, but employs visualization of the needle placement. My second finding occurred after I performed many successful procedures over the course of several months at the cervical and thoracic spine. Tuohy, Hustead, Sprotte, and other epidural needles have shorter, more angulated, and less sharp bevels in order to minimize the chance of inadvertent puncture of the dura matter and to facilitate LORT. I found that the 22g Quincke needle works better with CST than the 20g Tuohy epidural needle. A Quincke needle with a bent tip is much easier to maneuver and navigate toward the desired spot under fluoroscopy than a thicker, straight epidural needle. This is important at the cervical spine, where spaces are small and accuracy of needle placement is critical (Figure 1). The bent-tip Quincke needle makes a challenging procedure possible when attempting to place the needle between angulated spinal processes at the thoracic spine. I found that my success rate with thoracic epidurals became higher after I substituted the Tuohy needle with the Quincke. With CST, one may see the spread of the contrast into an epidural space, as well as into soft tissue when only the very edge of the needle’s bevel is inside the epidural space and the rest is in soft tissue. This would follow with classic contrast spread into an epidural space with minimal needle advancement. In my view, the short-beveled sharp cutting needle would be more advantageous than the Quincke needle for the purpose of CST.
It is not a goal of this letter to change common practices in epidural injections. LORT is safe and reliable in experienced hands and one cannot consider himself a pain practitioner until he masters it. There is no substitute for LORT with spinal cord stimulator trials or when epidural injection has to be done blindly, as, for example, in labor epidurals. However, it is my belief that CST could be an alternative to LORT in challenging cervical and thoracic procedures. With advances in fluoroscopy and in our understanding of imaging of the spine, it may become a helpful tool for pain practitioners to recognize epidural space while performing spinal injections.