15 Injection-Based Spine Procedures and Diagnostic Procedures

It is important the clinician understands the medications that are used in spinal injections. This section will give a brief overview of some medications in each category, but is by no means a comprehensive list. The clinician should refer to the official prescribing information for each drug. These can be found in the published manufacturer product information as well as the Physicians’ Desk Reference.¹

Local Anesthetic

A local anesthetic reversibly blocks neural sodium channels to interrupt nerve impulse conduction. The two most commonly used local anesthetics, lidocaine and bupivacaine, are amides. Lidocaine has a faster onset and shorter duration of action² ( Table 15.1). Bupivacaine is more lipid soluble, so it is more potent and has a longer duration of action than lidocaine. Both are metabolized by the hepatic cytochrome P450 system as well as conjugation. Because of this, caution should be used in patients with liver dysfunction. Because of potential adverse reaction with intravascular injection of a vasoconstrictor (i.e., epinephrine) or perineural injection of preservative (e.g., methylparaben), it is generally recommended to do spinal injections with preservative-free and vasoconstrictor-free medications. Because the local anesthetics are slightly acidic to enhance stability, which can cause a burning sensation when first injected into the skin and subcutaneous tissue, a small amount of sodium bicarbonate 8.4% can be added to the local anesthetic (1:20 volume ratio) to decrease the initial burning.^3,4 This must be done carefully since adding too much sodium bicarbonate can cause drug precipitation.

Corticosteroids

Glucocorticoids are anti-inflammatory by decreasing the local production of inflammatory medications such as prostaglandins, leukotrienes, interleukin 1, interleukin 6, and tumor necrosis factor α.^5,6 Glucocorticoids are metabolized by the liver and excreted in the urine. They also transiently elevate blood glucose level, so they must be used with caution in patients with diabetes mellitus.⁷

The selection of the steroid to be used depends on the injection to be done. Commonly used corticosteroids include methylprednisolone acetate (Depo-Medrol), triamcinolone acetonide (Kenalog), and dexamethasone sodium. In general, nonparticulate steroids have been demonstrated to dissipate rapidly and therefore may have a limited duration of effect.⁸ Because of this, even though there is no randomized controlled trial verifying this, it is felt particulate steroids are longer acting.⁹ Thus, if there is no major risk of cerebral or spinal cord infarcts, it is reasonable to consider using particulate steroids.

However, with cervical and thoracic epidurals, injection of particulate corticosteroids into a vertebral or foraminal artery can cause brain and spinal cord infarcts. It is felt the smaller particle size could decrease the risk of a clinically significant infarct. Dexamethasone sodium phosphate particle size is smaller than red blood cells and the particles did not aggregate. Triamcinolone acetonide and betamethasone sodium phosphate showed variable sizes. They aggregated and some particles were larger than red blood cells. Methylprednisolone acetate did not aggregate, and the majority were smaller than red blood cells.¹⁰ This was verified that same year in an animal study injecting corticosteroids in the vertebral arteries of pigs. Methylprednisolone was injected into four pigs causing severe stroke and failure to ventilate, dexamethasone was injected into four pigs causing no symptoms or transient symptoms that resolved in 2 hours, and prednisolone caused no symptoms.¹¹ In this situation, it may be prudent to use nonparticulate steroids with cervical and thoracic epidurals. Because local injection of corticosteroids into the skin can cause skin depigmentation, anytime corticosteroids are injected, the needle should be flushed with a small amount of local anesthetic or contrast before the needle is pulled to the skin.¹² Alternatively, if infection is not a major issue, and good sterile technique is practiced, the stylet can be reinserted into the needle before the needle is withdrawn.

Contrast

Contrast agents are used with fluoroscopic images to help verify the location of the needle tip. With joint injections, it helps determine if the tip is intra-articular. With epidurals and medial branch blocks, it also helps verify whether the tip is not intravascular. Nonionic water soluble iodine-based contrast agents are less irritating and allergenic than ionic iodine-based contrast. Two commonly used agents are iohexol (Omnipaque) and iopamidol (Isovue). These agents are excreted by the kidney. Potential side effects include headaches, nausea, vomiting, and central nervous system disturbances.¹³

For patients with anaphylactic allergic reactions to iodinated contrast, gadolinium contrast could be considered. This contrast is not as radiopaque as iodine-based contrast agents, so the contrast is harder to visualize than iodinated contrast. Also, gadolinium should not be injected intrathecally since this is irritating to nervous tissue and high doses can cause seizures.¹⁴ However, injection of low volume (0.5 mL) of gadolinium was reportedly done with low risk of complications.¹⁵

15.1.2 Fluoroscopic Guidance

Fluoroscopic guidance is important to confirm accurate needle position in the correct anatomic location. It has been shown that with blinded interlaminar epidurals, 20 to 30% were not properly placed when done without fluoroscopic guidance.^16,17 With blinded caudal epidurals, new clinicians had a 48% rate of improper needle placement, but experienced clinicians still had a 38% rate of improper needle placement.¹⁸ With sacroiliac joint injections, there was only a 78% rate of nonarticular injection with a blinded technique.¹⁹ Fluoroscopic guidance not only helps with improving needle placement accuracy, but also helps with decreasing the risk of intrathecal injection and intravascular injection.²⁰

Fluoroscopic guidance can also help make sure the needle tip is not in a blood vessel. Even when the needle was correctly placed in the spinal canal with caudal epidurals, the presence of blood on the needle stylus was not a reliable indicator of venous placement, so venous injection was done 9.2% of the time with blinded caudal epidurals.¹⁸ More recently, it was shown that for lumbar transforaminal epidural injections, live fluoroscopic imaging was better at detecting intravascular needle placement, and even doing intermittent fluoroscopic images 1 second after contrast injection missed 57% of the vascular injections of contrast.²¹ To help minimize radiation exposure to the hand, it is recommended to use a 6- to 12-inch extension tubing so the injecting hand can be kept out of the fluoroscopic image. It is not recommended to keep the hand in the fluoroscopic image with radiation gloves because the machine may then increase the fluoroscopic radiation output exposing the patient and clinician to more radiation.

Also, radiation exposure should be kept “as low as reasonably achievable” (ALARA). Only 2 to 3 seconds of live fluoroscopic imaging with contrast injection is necessary to determine if there is intravascular uptake. Similarly, a minimal amount of contrast is needed to determine proper needle tip location with joint injections to allow more room for the medications to be injected. If the contrast shows the needle tip is in the wrong location, less contrast injection will obscure less of the image area, making it easier to redirect the needle to the correct target.

15.1.3 Skin Preparation

The goal of skin preparation is to remove transient and pathogenic flora.²² The ideal agent should be safe and effective, quick acting, and inexpensive.^22,23 The most commonly used agents are alcohol, povidone-iodine, and chlorhexidine gluconate. Seventy percent isopropyl alcohol after 2 minutes kills 90% of the bacteria on the skin.²² Some reviews felt that chlorhexidine was more effective than iodine.^24,25 However, other reviews using more stringent criteria felt no conclusions could be drawn regarding using povidone-iodine versus chlorhexidine for reducing surgical site infections.^26,27 Good skin antisepsis, sterile drapes, and sterile technique should be used with all spinal procedures.

15.2 Pre- and Postprocedure Care

15.2.1 Basic Needle Control Techniques Effect of Bevel Tip on Needle Direction

Most spinal injections are done using a bevel-tip needle. If the needle is of larger caliber (22 gauge or smaller), the needle is less likely to bend during the procedure and the clinician can directly redirect the needle in the tissue with direct pressure. This is fine with procedures such as medial branch blocks, interlaminar epidurals, or hip joint injections where the path to the target location is fairly straight and it does not matter the direction the needle tip reaches the target. With smaller caliber (23 gauge or larger) bevel-tip needles, when the needle is advanced, it will generally move directly away from the beveled side (also generally away from the notch of the hub/stylet). This effect is less pronounced in tissue with less resistance such as adipose tissue and is more pronounced in tissue with more density such as muscle tissue and connective tissue.

Techniques for Advancing a Needle Tip in One Direction

With advancing a needle, the tip will tend to move away from the bevel (hub notch) at an angle based on the tissue density. If the needle is desired to be directed more in that direction, the exposed part of the needle could be bent in an arc and translated away from the desired direction of motion.²⁸ If the needle is desired to be directed even more laterally in that direction, the skin at the needle insertion site can be tractioned in the opposite direction of the desired direction of motion.

For procedures such as transforaminal epidurals and discograms especially at the L5–S1 level, it is also commonly useful to be able to direct the needle around bony tissue and still successfully direct the needle tip to the target. In these cases, it is useful to use smaller caliber needle (e.g., 23- or 25-gauge needles) with a bent tip ( Fig. 15.1). From the author’s experience, using a 25-gauge, 3.5-inch Quincke tip needle is the best choice for most procedures. Some use 27-gauge needles, but these needles have much less stiffness so that even with a bent tip, the needle may tend to advance only along the patient’s tissue planes making it harder to steer to the desired target. If a longer needle needs to be used, using a 25-gauge 5- to 6-inch Quincke tip needle or 23-gauge 6-inch Quincke tip needle is the best choice. When trying to do a transforaminal epidural injection after posterior fusion, if the postoperative scar tissue in the paraspinal muscles is very dense and directs the needle tip in the wrong direction, a 22-gauge Quincke tip needle may be the best choice. With epidurals, medial branch blocks, and medial branch radiofrequency neurotomy, the bent tip is useful once the tip is at the target location, since, if the injection of contrast shows intravascular flow, the needle can be easily readjusted 1 to 2 mm by pulling a few millimeters, then rotating the needle and readvancing to the target depth to try to get out of the blood vessel.

Bending the Needle Tip

In general, since the bevel is on the same side of the notch in the hub, to augment the direction the needle prefers to normally move when advanced, the needle tip is bent away from the bevel (away from the notch in the hub). There are several ways to bend the needle tip. One way is to hold the tip of the needle between the thumb and second digit of one hand and then hold the hub of the needle with the other hand and then bend the needle ( Fig. 15.2a). A second way, using one hand, is to hold distal end of the needle with the thumb on one side and the second and third digits on the other side. The thumb then applies pressure on the needle, bending the needle tip ( Fig. 15.2b). With these two techniques, the bend usually occurs about 10 mm from the tip. If more precise needle control is needed, it is better to bend the needle tip about 4 to 5 mm from the tip. This can be accomplished by using a needle driver to gently grasp and bend the needle tip. Some use the needle driver or another hard sterile metal instrument to push the tip flat on the procedure tray and then bend the needle up with the other hand. However, this author does not do this since pushing the needle down against the procedure tray may puncture the sterile drape and contaminate the needle tip. Another technique is to insert the tip of the needle about 3 to 4 mm into the tip of a larger caliber needle such as an 18-gauge needle and then bend the tip ( Fig. 15.2c). When bending the needle tip using the last three techniques, the needle should only be bent about 10 to 15 degrees at one location because bending further can cause the needle to catch the stylet. If a larger angle is desired, a second bend can be done about 1 to 2 mm closer to the tip than the first bend. Fig. 15.3 shows some commonly used needles for spinal injections. A 22-gauge needle is harder to bend by hand and may need to be bent using the latter methods described above.

Fig. 15.1 The effect of bent tip on needle trajectory. Using a flank of corned beef as the medium, with all three 25-gauge needles starting in the same angle and then advancing 1 inch, the straight needle (a) curves a little, the needle with a bend 10 mm from the tip (b) curves a little more, and the needle with a bend 4 mm from the tip (c) curves the most. In denser tissues, the needles would curve even more. In loose tissue such as adipose tissue, all three needles may not curve much at all.

Fig. 15.2 (a) Bending the needle tip with two hands. One hand holds the needle tip between the thumb and second finger. The other hand holding the hub is pulled so the needle tip is bent away from the bevel. (b) Bending the needle tip with one hand. One hand holds the needle tip with the second and third finger on the bevel side and the thumb on the other side. The thumb applies pressure so the needle tip is bent away from the bevel. (c) The needle tip is inserted into the tip of a larger caliber needle of about 3 to 5 mL. The needle is then bent so the tip is bent away from the bevel. The tip should only be bent about 10 to 15 degrees at one location. Bending the needle more than 15 degrees at one location can catch the stylet, making it hard to remove and reinsert.

Fig. 15.3 Different needle configurations for spinal injections. (a) 22-gauge, 3.5-inch Quincke tip needle with a straight tip; (b) 25-gauge, 3.5-inch Quincke tip needle with a straight tip; (c) 25-gauge, 3.5-inch Quincke tip needle with a bend 10 mL from the tip; (d) 25-gauge, 3.5-inch Quicke tip needle with a bend 4 mL from the tip; (e) 18-gauge, 3.5-inch Tuohy needle; (f) 20-gauge 5-inch Quincke tip needle; (g) 25-gauge, 8-inch Quincke tip needle with a bend 3 mL from the tip; (h) 25-gauge, 8-inch Quincke tip needle with a gradual bend about 1 inch from the tip.

The caudal epidural was first reported in 1901.²⁹ Corticosteroids were not added to the local anesthetic until 1952.²⁰ The volume of injectate reported ranged from 5 to 25 mL.²⁰ However, more recent data allow the clinician to better determine how much volume to inject. Freeman et al³⁰ showed using live fluoroscopic images of caudal contrast injection that at most 3.8 mL of contrast injection was needed to reach the L5–S1 disc space and 5 mL was needed to reach the L4–L5 disc space. Manchikanti et al³¹ assessed filling patterns of the lumbosacral epidural space by injections of different volumes of nonionic contrast. They showed increased filling of up to 10 mL of contrast injection at the S1 level. However, good filling was seen in 82% at the S1 level and only in 12% at the L5 level in nonsurgical patients.³¹ Because of this, caudal epidurals are more appropriate for pathology in the sacral region or lower lumbar region.

With the patient in the prone position (or lateral decubitus position if the patient cannot lie prone), the area just inferior to the sacral hiatus is palpated and highlighted on anteroposterior (AP) and lateral fluoroscopic view, and the skin over the area is prepared with 1 mL of 1% lidocaine using a 25- or 27-gauge 1.5-inch needle. A 25-gauge, 3.5-inch spinal needle is then directed about 30 to 45 degrees taken down through the sacral hiatus using multiple fluoroscopic images. The needle is then directed to enter the sacral spinal canal. The needle should be kept below the S2 level to decrease risk of intrathecal injection. If the patient’s symptoms are more to one side, the needle tip should be directed slightly to that direction since some patients have a dorsal median epidural septum that confines the spread of medication injected to the side ipsilateral to the injection.^32,33 Proper needle position is verified with two views. A 10-mL syringe should be used to ensure there is no blood flashback. Contrast should then be injected with live sequential fluoroscope imaging. This should highlight the nerve roots and epidural space without intravascular uptake ( Fig. 15.4). Injection is completed with 5 mL of a mixture of 1 mL of corticosteroid and 4 mL of local anesthetic. The needle is then flushed with a small amount of local anesthetic or contrast or the stylet is reinserted before the needle is completely removed.

Fig. 15.4 Caudal epidural. (a) Lateral view showing the needle passing thought the sacral hiatus. The tip should not extend above S2. (b) Anteroposterior (AP) view showing good contrast flow. The needle is kept to the right of midline since the patient’s symptoms were on the right side.

Interlaminar epidurals deliver medications into the posterior epidural space. Even though the injectate can flow anteriorly as it flows cranially, this does not always happen due to impedance from epidural fat, and the injectate may not reach the anterior space at the level of injection.³⁴ In the lumbar spine, any level can be chosen based on the clinical situation. In the cervical spine, injections should not be done at a level with central stenosis less than 8 mL due to risk of causing an epidural hematoma.³⁵

Loss of Resistance Technique

With the patient in a prone position, the interlaminar space is identified on AP view. The skin and soft tissue along the planned injection route is prepared with 1 mL of 1% lidocaine. A 18-gauge, 3.5-inch blunt tip needle (usually either a Tuohy needle or pencil tip needle) is then taken down to the interlaminar space using multiple fluoroscopic images on AP view to verify the needle is directed to the upper portion of the lower laminar. Once the needle is close to the epidural space, a lateral view should be used to determine proper depth since the ligamentum flavum is located at the anterior aspect of the spinous processes. The needle is then redirected a little cranially to walk off the lamina into the interlaminar space. Loss of resistance with either air or saline ensures the tip passes the ligamentum flavum and is in the epidural space. Proper needle position should be verified with two views. There should be no bloody flashback and injection of nonionic contrast with live sequential fluoroscope imaging verifies epidural flow without intravascular uptake ( Fig. 15.5). The injectate should be a corticosteroid with or without local anesthetic. The needle is then flushed with a small amount of local anesthetic or contrast or the stylet is reinserted before the needle is completely removed.

Fluoroscopy with Cervical Interlaminar Epidurals

Because the epidural space is larger in the lower cervical spine, cervical interlaminar epidurals are usually done at the C7–T1 level. However, because there is more dense tissue at the T1–T3 levels with the shoulders, it is commonly harder to visualize the needle tip in the C7–T1 epidural space on lateral view. Two ways to help with visualizing the needle tip include depressing the patient’s shoulders to the foot so they overlie the target area less as well as moving the fluoroscope toward the foot so more shoulder is visualized, which will cause the machine to increase the power used.³⁶ Another help is a spinal positioning platform (Oakworks Medical) which is placed under the patient’s chest when lying prone, and allows the shoulders to fall forward so they are not overlying the target C7–T1 epidural space.

Hanging Drop Technique

The hanging drop technique was described by Gutierrez.³⁷ This technique relies on the presence of negative pressure in the epidural space when the patient is sitting in the cervical and upper thoracic spine.³⁸ Because of this, this technique should not be considered in the lumbar region. With the patient sitting up, a needle is directed to the C7–T1 interspace. Once the needle is in the interspinous ligament, the stylet is removed and a drip of saline or local anesthetic is placed on the hub. The needle is slowly advanced. When the needle passes the ligamentous flavum, the negative pressure in the epidural space draws the drop of fluid into the needle. If available, a Weiss needle should be used for this technique since the two side flaps at the hub allow the clinician to better control the advance of the needle.³⁹ If fluoroscopy is available, it should be used to improve safety and efficacy. The ligamentum flavum cannot be seen, but lies at the anterior aspect of the spinous processes.

15.3.3 Transforaminal Epidurals

Lumbar Transforaminal Epidural Steroid Injection

With the patient in the prone position, the location of the neuroforamen just inferolateral to the corresponding pedicle is identified at about 15 degree lateromedial oblique view ( Fig. 15.6a). The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle is then taken down to the neural foramen’s most superior aspect just inferior to the pedicle using multiple fluoroscopic images ( Fig. 15.6b). When the needle tip is about 1 inch from the target, AP views should be used to make sure the needle tip is always kept lateral to the 6 o’clock position of the pedicle on AP view ( Fig. 15.6c). Proper needle position is verified with two views ( Fig. 15.6c, d). Derby et al reported the safe triangle in the superior neuroforamen region as a good anatomic target for lumbar transforaminal epidurals that minimizes the risk of hitting the exiting nerve root or puncturing the thecal sac.⁴⁰ The medial point of the triangle is the bottom of the pedicle with a base running inferolaterally where the nerve root runs and the lateral side is the outer margin of the intervertebral foramen. Later, Jasper and then Choi et al^41,42 reported a second anatomic target, the retrodiscal space in the inferior neuroforamen previously described as Kambin’s triangle ( Fig. 15.7), that is useful especially at the L5–S1 level where the patient’s anatomy can make the safe triangle difficult to reach as well as the upper lumbar region to avoid the artery of Adamkiewicz, which unfortunately tends to be present in the upper part of the neuroforamen.^{41,42,43,44,45} There should be no bloody flashback, and injection of nonionic contrast with live sequential fluoroscope imaging verifies epidural flow without intravascular uptake ( Fig. 15.6e and Fig. 15.7c). The injectate should be a corticosteroid with or without local anesthetic. If the level injected is the L2–L3 neuroforamen or more cranial, because of the risk of the artery of Adamkiewicz being present, a small particulate steroid such as dexamethasone should be considered.^10,11,43,46 Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted.

Fig. 15.5 Interlaminar epidural. (a) Lumbar lateral view. (b) Lumbar AP view. (c) Thoracic lateral view. (d) Thoracic AP view. (e) Cervical lateral view. (f) Cervical AP view. If using a Tuohy needle, the needle is advanced from a caudal to cranial direction with the curved (blunt) side of the tip facing the spinal canal to decrease the risk of puncturing the dura mater. The needle tip should stop around the anterior aspect of the spinous processes. The cervical later view can still be hard to visualize even with moving the view to the thoracic level and using a spinal positioning platform.

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