How is needle navigation performed in therapeutic injections for pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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Answer

Answer

Knowing how to manage the bevel of the outer cannula and inner stylet are key to successful needle navigation. The hub of the needle usually has a notch that corresponds to the face of the bevel needle tip. After puncturing the skin, as the needle is advanced through the deeper soft tissues, the needle tip tends to veer slightly in the direction opposite to the hub notch; therefore, enter the skin as close to the target as feasible. The tendency for a needle to travel in a curved trajectory can be useful at times and can be enhanced by placing a small 5-10° bend in the tip. When traveling a significant distance with a bent needle tip, the needle must be continually rotated to prevent it from straying off course, which may cause significant tissue disruption.

To counter this potential problem, a larger coaxial needle can be placed just proximal to the target, and then if a curved trajectory facilitates steering just beyond the needle tip, a bent needle can be inserted through the larger needle, which allows it to swerve or turn in the direction necessary to reach the anatomical objective.

The needle hub is held with the thumb on top pointing toward the notch. The index and middle fingers are place opposite the thumb at the junction of the hub and needle. The needle is pushed by the thumb and can be steered by turning the notch in a direction that is 180° opposite to the target. This maneuver places the sharp edge of the needle tip toward the direction that the needle is intended to travel. The stylet should always be contained entirely within the cannula while the needle is moving forward.

Before skin entry, the angle of the needle tip and its trajectory define its course. However, after the needle passes into deeper soft tissues, it cannot be steered by redirecting or pushing it sideways. Bowing of the needle is a technique, whereby, pressure is established both at the skin surface and at the proximal end of the needle. The needle bows toward the surface pressure. The hub is moved in a direction opposite to the notch, causing the needle to arc and the needle tip to travel in the same trajectory as the bow, opposite to the notch. Turning the hub changes the course of the needle, but always in a direction that is opposite to the bowed posture of the needle. See images below.

Needle tracking paths with bevel alone, bevel plus Needle tracking paths with bevel alone, bevel plus bend and rotation
Pushing sideways on a superficial needle changes t Pushing sideways on a superficial needle changes the needle tips' direction. Pushing sideways on a deep needle bends the needle shaft without changing direction of tip.
Changing the needle's direction when needle tip is Changing the needle's direction when needle tip is deep. Technique of bowing the needle shaft changes the direction of a deep needle tip.

The needle should always be advanced slowly over short distances with frequent monitoring by fluoroscopy. The operating practitioner needs to be aware to move his hands out of the path of the x-ray beam when using intermittent fluoroscopy. The needle tip position can be determined by tissue feel (soft tissue vs bone), fluoroscopic visualization [lateral, oblique and AP planes] and using radiopaque contrast. Fluoroscopic localization requires an AP and lateral of the needle or one fluoroscopy view and contact with an identifiable bony landmark. Contacting bone during the procedure offers a unique opportunity to know needle tip position.

Also, when the needle tip is resting on bone, it is unlikely to be in a dangerous venue, such as a blood vessel, neural tissues, or the intrathecal space. Injection of radiopaque dye can be used to further establish certainty of the needle location. Water-soluble contrasts are benign, even when injected into the intravascular or intrathecal space; however, the presence of contrast may obscure view of the needle's tip for continued placement. The operator must know the needle tip's location before injecting any active medication. If injected radiocontrast dye washes away rapidly from the needle tip during the injection be wary, because the contrast may be entering a blood vessel. The dye should stay at the injection site. [2]


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