Spine Injections

Back pain is one of the most common reasons for patients to seek medical attention. About two-thirds of adults will experience low back pain at least once in their lifetime (Rubin 2007).

Its etiology is often unclear given that similar complaints and symptoms may result from various pathologic conditions and imaging studies do not always correlate. This makes accurate diagnosis and treatment difficult. Occupational injuries, compensation, and secondary gain issues confound the situation even more. A thorough history and physical examination, as well as development of a cohesive and consistent treatment plan incorporating diagnostic procedures and therapeutic interventions yield the most effective care (Waldman 1996) (Table 13.1).

Back pain can be generalized into two categories, axial and radicular, but patients commonly have components of both. Axial back pain commonly originates with the facet joints but can be secondary to pathology related to the intervertebral disk. Radicular pain usually results from nerve root irritation which may be the end result of many different processes. There are different approaches to diagnosis and treatment of axial and radicular back pain through interventional procedures, but significant overlap exists. Patient responses to the procedures are difficult to predict, and evidence-based outcomes are difficult to interpret.

Table 13.1 Diagnostic tests in patients with back pain.

Diagnostic test

Accuracy (%)

Sensitivity

Specificity

Clinical examination

46-76

0.80

0.82

Radiography

34

-

-

Myelography

72-91

0.67-0.95

0.76-0.96

CT/MRI

70-100

0.80-0.96

0.68-0.95

Discography

30

0.83

0.63-0.78

Electromyography

78

0.66-0.72

-

CT - computed tomography; MRI - magnetic resonance imaging. Adapted from Rubin (2007).

CT - computed tomography; MRI - magnetic resonance imaging. Adapted from Rubin (2007).

Epidural Steroid Injections

Interlaminar, Transforaminal, and Caudal Epidural Steroid Injections

Indications

Epidural steroid injections (ESIs) are the most commonly performed injection for back pain. They may be performed in all segments of the spine, but are most commonly done in the lumbar and cervical regions. The usual approach is through the interlaminar window, but this is not always possible. Removal of bone and ligament, hardware implantation, and postsurgical scarring can make the interlaminar approach both difficult and risky. Transforaminal, caudal, and sacral approaches to steroid injections may be necessary due to the anatomic alterations or pathologic changes in the spine. Clinical practice data have shown that cervical interlaminar ESI is safer than cervical transforaminal injection. Lumbar interlaminar ESIs compared with lumbar transforaminal injection are equally safe and efficacious.

Interlaminar ESI

Technique

The interlaminar ESI is usually performed in the prone position under fluoroscopic guidance. The targeted level is identified by counting the lumbar or cervical vertebrae from a known level such as T1 (first rib-bearing vertebrae), T12 (last rib-bearing vertebrae), or the skull or sacrum. Anatomic variants such as a sacralized L5 or a lumbarized S1 may be present, so counting up and down is recommended. After a prep and drape and under standard sterile technique, the skin is anesthetized and a Tuohy needle (18 or 20 gauge) is advanced through the skin and interspinous ligament until the ligamentum flavum is engaged. The loss of resistance technique with saline or air is used to access the epidural space. In the cervical spine the hanging drop technique may also be used. The needle tip location is confirmed with a lateral film and also by injection of radio-opaque contrast, which shows a characteristic pattern (Fig. 3.18). The steroid is then injected, followed by a small amount of preservative-free saline or local anesthetic. The addition of local anesthetic not only provides some immediate pain relief but also increases the risk of post-injection weakness. It requires monitoring after the procedure for prolonged weakness or potential intrathecal injection. The injections are targeted at or below the corresponding level of the symptoms and the pathology shown on imaging. Severe stenosis or disk herniation would suggest injection below the level, as risk of

Side Effects Facet Injections
Figure 13.18 Cervical epidural injection at C7-T1 interspace with spread of contrast outlining fat globules in the epidural space.

a wet tap or neurologic injury is increased. The effects of the steroid usually occur within 2448 h and reach their maximum potential benefit by 7-10 days. They may be repeated monthly up to three times per year without significant systemic side effects from the steroids. Diabetics may experience elevated blood glucose levels for up to several weeks.

Transforaminal Injections

Transforaminal steroid injections target the nerve root laterally as it exits the neural foramen created between two vertebral segments. Depending on practice, they are performed for the same indications of intralaminar injections or after failure of interlaminar injections. Additionally, transforaminal injections are utilized in patients whose anatomy does not allow for safe performance of the interlaminar approach. A 22-gauge spinal needle is used to approach the nerve root in the foramen. A fluoroscopic view about 22° lateral oblique shows the characteristic "scotty dog" appearance of the vertebral body and pedicle. The needle is advanced toward the "neck," or 6 o'clock position just beneath the transverse process. This area above the nerve root is considered safer with respect to risk for intravascular injection and contact with the nerve root itself. This approach is also used for diagnostic nerve root blocks utilized in preoperative planning.

Complications

Intravenous injection is prevented with contrast dye. Intraneural injection can be reduced following present American Society of Interventional Pain Physicians guidelines that require a patient be communicative, such that initiation of an intraneural injection will be met with a scream of discomfort from the patient and cessation of injection at that anatomical point.

Intra-arterial injection of particulate steroids in this approach can cause spinal cord infarction. The use of contrast to assess for vascular runoff and verify spread along the nerve root and even to the epidural space is a must. It should be noted that the risk of intra-arterial injection is even higher when performing transforaminal injections in the cervical spine (Figs. 13.19 and 13.20). Cervical epidural injection with the use of a lateral view can reduce risk of inadvertent improper location of injection and mitigate the risk of catastrophic cord injection.

Transfaraminar Injection Xray Scottydog
Figure 13.19 Fluoroscopic image of left C6 nerve root injection.

Caudal ESI

The caudal ESI delivers steroid to the epidural space by entry through the sacral hiatus. The external palpable landmarks to this are the sacral cornu and the tip of the coccyx, and a lateral fluoroscopic view is very helpful in directing the Tuohy needle. After a prep, local anesthesia, and fluoroscopic views AP and lateral are obtained, the Tuohy needle is advanced through the skin just below the sacral hiatus and advanced to the sacrococcygeal ligament. The needle approach angle is then flattened almost to the same axis as the patient and advanced through the ligament. The injection may be delivered via the needle at this location or an epidural catheter may be advanced further to a more cephalad location. Dye may be used to confirm the spread, and a flush with 7-10 ml of preservative-free saline also helps to achieve cephalad spread of the medication.

Catheter Epidural
Figure 13.20 The arrows are pointing to the left L3-4 and L4-5 facet joints. From this angle a transforaminal or nerve root injection for L4 would be made at the dot.

Epidurolysis

Epidural fibrosis or "adhesions" may form spontaneously or after a surgery. They may cause back pain or radicular symptoms in addition to limiting the effectiveness of epidural injections. The adhesions can restrict the flow of medication to the nerve roots thus limiting their spread and absorption. Epidural lysis of adhesions is a percutaneous procedure with parts similar to an epidural steroid injection. It may be performed from the sacral, interlaminar, or transforaminal approaches. With the patient prone under fluoroscopy, a Tuohy needle is used to access the epidural space and a steerable catheter is advanced in the epidural space to the affected area. Injection ofcontrast shows characteristic filling defects which are the target of the procedure. Repeated passes of the catheter in combination with injection of large volumes of saline are administered in attempts to disrupt the fibrosis tissue. The injectate may be normal or hypertonic saline sometimes in combination with hyaluronidase which softens scar tissue. It may be followed by steroids and or local anesthetic. The catheters may be left in place for repeated treatments over a several-day period (Racz et al. 2008). An additional approach to perform the lysis of adhesions is done under direct visualization called epiduroscopy. A flexible scope is inserted into the epidural space via the caudal approach to the sacral hiatus. Pressure from the scope in combination with infusions of saline is used to break adhesions.

Caudal Block Fluoroscopy
Figure 13.21 Fluoroscopic image of caudal approach to epidural steroid injection. Radio-opaque catheter and contrast display a characteristic "Christmas tree" pattern outlining the sacral roots.

Complications include dural puncture, headache, epidural abscess, bleeding, sensory deficit, and catheter shearing. The procedure may be repeated several times in a year (Geurts etal. 2002) (Fig. 13.21).

Sacral Nerve Blocks Indications

Sacral injections through the S1 foramen can be used to deliver steroids to the epidural space if other approaches are not technically feasible. A spinal needle is advanced into the superior aspect of the foramen under fluoroscopy, and contrast is injected to verify epidural spread.

Complications

The risks of the above injections vary in degree based on the approach. They include bleeding, infection, dural puncture causing CSF leak and headache, weakness, increased pain, nerve damage, and medication reactions.

Facet Joint Injections Indications

The facet joints are small synovial joints located between each vertebrae posteriorly and are implicated in axial back pain.

Anatomy

They function in alignment of the spine and allow for forward flexion and extension and smaller amounts of lateral flexion, extension, and rotation. Abnormalities in their structure and alignment may cause substantial discomfort which follows a characteristic referral pattern. After a failure of conservative measures, injections are targeted into the joint itself or to the sensory innervation of the joint (Figs. 13.22 and 13.23).

Cervical Facet Joint Referred Pain

Figure 13.22 Pain referral patterns from cervical facet disease. Technique

Facet injections are performed in the prone position under fluoroscopy with a spinal needle. It is directed into the joint space which can only support 1-2 ml of fluid. Diagnostic injections would include LA alone, while a mixture of LA and steroid provides longer relief. Each facet receives sensory innervations from the dorsal nerve root above and below it (Raj et al. 2002) (Fig. 13.24). These nerves, the "medial branches," may be anesthetized with local anesthetic diagnostically as well. This block establishes not only the specific contribution of the injected facet joint to the patients overall back pain but also the ability to treat them with radiofrequency neurolysis. The procedure is performed under fluoroscopic guidance in the prone position. A spinal needle is directed to the lamina where the medial branches come off the dorsal roots at levels above and adjacent to each symptomatic level. A small amount of long-acting LA, usually less than 0.5 cc, is injected to anesthetize each medial branch. Pre- and post-injection pain scores and level of function are compared to establish efficacy, and patients also track their pain over the ensuing hours during normally painful activities. Response to the MBB's correlates a response to radiofrequency neurolysis. Because of the potential for false positives, the right and left sides may be blocked separately, and

Anterior Posterior

Figure 13.23 Pain referral patterns from the lumbar facet joints. In descending order, the most common referral patterns extend from the darkest (low back) to the lightest regions (flank and foot).

Anterior Posterior

Figure 13.23 Pain referral patterns from the lumbar facet joints. In descending order, the most common referral patterns extend from the darkest (low back) to the lightest regions (flank and foot).

it has been suggested that a second diagnostic block be performed to confirm the diagnosis (Schwarzeret al. 1994) (Fig. 13.25).

Due to the anatomic differences between the vertebrae in the different regions of the spine, the approach to the medial branches varies. In the cervical spine there are no distinguishable transverse processes as landmarks. The needle is directed to the groove formed between the superior and the inferior articular processes at each level visualized by a 10° medial oblique angle (Fig. 13.26).

Cervical Facet Injections

All the cervical joints are true joints since they are lined with synovium and have a capsule, except for the Atlanto-occipital and the Atlanto-axial joints. Cervical facet blocks can be done by the intra-articular technique as well. This can be achieved by means of a "blind" technique where the point of entry of the needle is two spinal levels below and 2.5 cm lateral to the facet joint to be blocked. An 18-gauge needle is used as an introducer, and a 25-gauge 3.5-in. styletted spinal needle is inserted to reach the area below the joint to be blocked. As the needle is advanced, a pop is felt when the spinal needle enters the facet joint. Two cubic centimeters of preservative-free local anesthetic is injected into the joint for pain relief. In the presence of inflammation, 80 mg of depot steroid can be added for the first block and 40 mg of depot

Innervation Faccet Joints
Figure 13.24 The facet joints are innervated by the medial branches of the dorsal ramus from the level above and same level as the joint.
Needles Facet Medial Branches Dual
Figure 13.25 The arrow indicates the left pedicle on L4, and the dot indicates the location for a medial branch block in the lumbar region.
Figure 13.26 Fluoroscopic image of the C-spine from a 10° oblique angle to visualize the MBB target groove between articular processes.

steroid can be added for the consequent block. Many practitioners utilize larger volumes (up to 5 ml) for bathing of associated ligaments, paraspinal muscles, and support structures which can provide additional beneficial affects.

Thoracic Facet Block: Medial Branch Technique

Indications

The medial branch technique is the most common technique for treating thoracic facetogenic pain syndrome. Physical examination with pain on facet loading or a Kemp's test is highly suggestive of a facetogenic mediated pain syndrome.

Technique

The patient is placed in a prone position, and the spinous process at the level to be blocked is identified. After anesthetizing the skin with 1% lidocaine, a 25-gauge 3.5-in. styletted needle is inserted through an 18-gauge introducer needle at a point 5 cm lateral and slightly inferior to the spinous process. The needle is pointed to the junction of the transverse process and the vertebra at the level to be blocked (Fig. 13.27). The needle is then advanced to the most lateral aspect of the border of the articular process. The stylet is removed, and if no blood or CSF fluid is observed after aspiration, about 1.5 cc of local anesthetic solution is injected. If an inflammatory process is suspected then depot steroid can be added with the local anesthetic usually 80 mg for the initial block and 40 mg thereafter. The block can also be done under fluoroscopic guidance with contrast medium injected before injection of the local anesthetic to ensure that the needle is not in the intrathecal space.

Med. br. dorsal ramus Dorsal ramus

Ventral ramus (intercostal n.)

Sup. articular process

Lat. br. dorsal ramus

Figure 13.27 Thoracic facet block: medial branch technique.

Med. br. dorsal ramus Dorsal ramus

Ventral ramus (intercostal n.)

Sup. articular process

Lat. br. dorsal ramus

Figure 13.27 Thoracic facet block: medial branch technique.

Thoracic Facet Block: Intra-articular Technique

The thoracic facet block can also be done by an intra-articular technique when the needle is inserted two spinal levels below and 2.5 cm lateral to the spinous process to be blocked. Similar to the medial branch technique, an 18-gauge 1-in. needle is used as an introducer for a 25-gauge 3.5-in. styletted spinal needle that is used for the block. The needle is advanced to impinge on the bone of the articular pillar and is advanced until it slides into the facet joint. After negative aspiration a total of 1 cc of local anesthetic is injected. If there is an inflammatory process then 80 mg of depot steroid can be added to the local anesthetic for the initial block and 40 mg of depot steroid for subsequent blocks. The procedure can also be done with fluoroscopic guidance and the injection of 1 cc of contrast medium before the injection of local anesthetic to ensure correct placement of the needle.

Lumbar Facet Joint Block Technique

The lumbar spine is visualized and approached from a 22° oblique angle. Thoracic facet disease is much less common but may be approached in a similar fashion. Patient participation during needle manipulation aids placement. Sedation can be used but is discouraged since it may alter subjective relief of symptoms (Cohen and Raja 2007).

Radiofrequency neurolysis or ablation (RFN or RFA) of facet joints is a neurodestructive procedure utilizing RF energy delivered through the tip of an insulated needle to a specific location, in this case the medial branch of the dorsal root which gives sensory innervation to the facet. After successful diagnostic medial branch blocks with local anesthetic, RF energy can be applied to the same location, achieving sensory denervation of the facet joint for a much longer duration. Both cervical and lumbar RFA of the medial branches have been

Lumbar Facet Block

Medial Branch Posterior Ramus
Figure 13.28 Lumbar facet block: radiofrequency lesioning of the medial branch of the primary posterior rami.

shown to be effective in multiple studies after a single successful diagnostic block (Leclaire et al. 2001, Tekin et al. 2007, van Kleef et al. 1999, van Wijk et al. 2005, Dreyfuss et al. 2002, Dreyfuss et al. 2000, Lord et al. 1996) (Fig. 13.28). Needle placement technique and target are the same as the medial branch blocks. After placement of the RF needle, testing is done to confirm a safe distance from both the dorsal and the ventral roots so that they are not damaged while treating the medial branch. Lesions are made by using high-frequency and varying current, maintaining a temperature of 80° C. The procedure is usually effective for 6-12 months or longer. A variation of the technique using pulsed radiofrequency at 2 Hz for 4 min at 42° C has also been shown to be effective (Tekin et al. 2007). Complications include pain, bleeding, infection, and nerve damage.

Genitofemoral Nerve Blocks Indications

This block is for the treatment of groin pain and genitofemoral neuralgia and also for the provision of surgical anesthesia for groin surgery and inguinal herniorrhaphy when combined with ilioinguinal and iliohypogastric blocks.

Anatomy

The genitofemoral nerve arises out of the L1 nerve root and also occasionally has a contribution from the T12 nerve root. It emerges on the abdominal surface opposite L3 or L4 and then divides into the genital branch and the femoral branch above the inguinal ligament. In males the genital branch passes through the inguinal canal.

Technique

The block is done in a supine position. In order to block the genital branch it is important to identify the pubic tubercle and the inguinal ligament. A point just lateral to the pubic tubercle below the inguinal ligament is the point of entry. A 1.5-in., 25-gauge needle is used to pierce the skin, and 5 cc of 1.0% preservative-free lidocaine is injected into the subcutaneous tissues after negative aspiration. In the presence of inflammation 80 mg of depot steroid can be used with the initial block and 40 mg of depot steroid with subsequent blocks.

Ilioinguinal Nerve Blocks Anatomy

The ilioinguinal nerve is a branch of the L1 nerve with occasional contribution from the T12. The ilioinguinal nerve pierces the transverse abdominis muscle at the level of the anterior superior iliac spine. It provides sensory innervation to the skin in the inner side of the upper thigh, the root of the penis, and the upper scrotum in males or the lateral part of the labia and the mons pubis in females.

Technique

To perform the block a point 2 in. medial and 2 in. inferior to the anterior superior iliac spine is identified. The area is prepped and draped in sterile fashion. A 25-gauge 1.5-in. needle is entered at the point identified and advanced obliquely toward the pubic symphysis. A total of 5-7 cc of 1% lidocaine is injected in a fan-like fashion to block the ilioinguinal nerve.

Iliohypogastric Blocks Anatomy

The L1 nerve root gives fibers to the iliohypogastric nerve. Contribution from the T12 is also seen in some patients. The iliohypogastric nerve perforates the transverse abdominis muscle and lies between this muscle and the external oblique muscle. The nerve divides into a lateral and an anterior branch. The lateral branch gives sensory innervation to the posterior-gluteal region, while the anterior branch provides sensory innervation to the skin above the pubis after piercing the external oblique muscle.

Technique

The block is performed by identifying a point 1 in. medial and 1 in. inferior to the anterior superior iliac spine. A 25-gauge 1.5-in. needle is inserted obliquely toward the pubic symphysis, and about 5-7 cc of 1% lidocaine is injected in a fan-like fashion. Methylprednisolone 40 mg can be injected with the local anesthetic if there is an inflammatory component to the pain.

Sacroiliac Joint Injections Indications

Sacroiliac (SI) joint dysfunction is a common cause of low back pain and also a frequently missed diagnosis. It occurs independently or in conjunction with facet disease, sometimes being confused with it. Physical examination with a positive Patrick's test is highly suggestive of sacroiliac joint-mediated pain. A local anesthetic block of the joint can be used to diagnose it, and steroids may be added to the injection for therapy.

Technique

With the patient positioned prone, fluoroscopy is used to visualize the joint space obliquely, medial to lateral. The joint is accessed in the inferior portion with a 22- or 25-gauge spinal needle. Intra-articular placement is verified with contrast. The joint has a large surface area, but not a tremendous capacity, so only a small amount, several cubic centimeters, of local anesthetic or LA/steroid is tolerated. RF treatment of the joint is also possible and has been shown to be effective versus placebo (Ferrante et al. 2001, Vallejo et al. 2006, Maugars et al. 1996). Standard RF lesions are performed at the L5 medial branch and along the medial portions of the S1 and S2 foramen. This covers the innervation of the upper half of the joint. Then two RF probes are used as bipolar leads to create lesions in a stepwise fashion along the SI joint from the mid portion to the bottom to continue the RF lesion for the remainder of the joint. A "railroad track" down the joint is made by successively placing the needles about 5 mm apart along the medial side of the joint from the mid portion to the inferior edge and creating lesions between them. Motor testing should be performed prior to treating the branches as described in RFN. The effects usually last for 6-12 months.

Cryoneurolysis

Cryoneurolysis is a neurodestructive procedure that uses cooling to induce nerve damage. The cryoprobes consist of an inner tube and an outer tube and a cooling chamber at the tip. They come in 12, 14, or 16 gauges. Either nitrous oxide or carbon dioxide is pressurized through the needle and tip which cools causing a 3.5-5.5 mm expansion of ice in the surrounding tissue. Like radiofrequency, there are several steps to the treatment procedure. First, a diagnostic block should be performed to identify the nerve location and contribution. On another occasion just before treatment, both sensory and motor stimulation should be performed. Lesions are made for 90-120 s. As the nerve regenerates the lesion can be repeated.

Discography

Discography is a diagnostic procedure used to identify pain-generating intervertebral disks in preoperative evaluation and planning. Under fluoroscopy with the patient prone, a needle is guided into the vertebral disk. Contrast dye is injected to verify placement of the needle into the disk. The disk is then pressurized via the needle in attempts to reproduce painful symptoms. The procedure is repeated at levels above and below, and pain scores are reported after injections into each level. Comparison is made from symptomatic to non-symptomatic or control discs. Due to the variability in technique and its basis on subjective patient reports, its use is limited (Fig. 13.29).

Intradiscal Electrothermal Therapy

Intradiscal electrothermal therapy (IDET) is a therapeutic technique used to treat discogenic pain. It involves passage of a catheter under fluoroscopy into the pain-generating ruptured intervertebral disk. The catheter is then heated to 80-90° for 5-6 min. This thermal treatment

Lumbar Sympathetic Block
Figure 13.29 Lumbar discogram.

is postulated to stop the disk contents from leaking as well as improve pain. Despite its initial popularity, its efficacy is inconclusive and because of patient discomfort and risk of diskitis its use has been limited (Bogduk et al. 2004).

Spinal Cord Stimulation

Spinal cord stimulation (SCS) is a treatment modality whereby electrical stimulation is applied to the dorsal columns of the spinal cord to treat pain by "covering" it with sensory interference. It is an "augmentation" therapy as compared to the "ablative" therapies previously mentioned performed by neurosurgery, but similar to the neurosurgical procedures in that it is an endpoint therapy. Although the actual mechanisms are not known, the theories initially spawned from Melzack and Wall's "gate control theory." Neuropathic, sympathetic, and nociceptive pain can all be treated with varying efficacy. Different theories exist for each of the different types of pain treated, but "the precise mechanism of action seems to be complex and may vary depending on the clinical condition for which the device was placed. A single, simple, unifying mechanism of action of SCS is not evident at this time (Schmidek and Roberts 2006)."

Refractory neuropathic pain after back surgery, post-laminectomy pain syndrome or failed back surgery syndrome, chronic regional pain syndrome (CRPS) (Kumar et al. 1997), and ischemic pain from peripheral vascular disease and refractory angina (Ansari et al. 2007) are the most common and very effectively treated with SCS (Bala et al. 2008). It is also used successfully in the treatment of diabetic neuropathy, posttherapeutic neuralgia, and limb amputation pain. Implantation of the electrodes outside the CNS has been valuable in the treatment of peripheral nerve injuries and occipital neuralgia (Jasper and Hayek 2008) (Fig. 13.30). Leads can also be placed subcutaneously for "field stimulation" in non-dermatomal pain syndromes.

Occipital Nerve Stimulation
Figure 13.30 Intraoperative film of bilateral occipital nerve stimulator leads, tip of the instrument is at the C1-C2 interspace.

Technique

The procedure involves several phases, but may be condensed depending on the institution. After appropriate patient screening process including a mental health evaluation (Prager and Jacobs 2001), a several-day stimulation trial is performed. Percutaneous implantation is performed in an operating room setting with the patient under a light anesthetic. With the patient prone, a Tuohy needle and the loss-of-resistance technique are used to access the epidural space several vertebral levels below the desired location. A shallow-angled approach minimizes movement at the skin. The lead is then threaded to the desired level and side adjacent to the dorsal columns with the aid of a steerable central wire and fluoroscopy (Figs. 13.31 and 13.32). Coverage is tested with patient participation so that the lead can be maneuvered for optimal pain coverage. The lead is carefully taped to the skin and attached to an external generator.

Pulse generator

Figure 13.31 Spinal cord stimulation (SCS) system diagram labeled.

Pulse generator

Figure 13.31 Spinal cord stimulation (SCS) system diagram labeled.

Spinal Cord Stimulataor Dual Lead

Intraoperative fluoroscopic image of dual percutaneous thoracic leads.

Figure 13.32

Intraoperative fluoroscopic image of dual percutaneous thoracic leads.

Complications

Complications include epidural hematoma and abscess, dural puncture, infection, and lead migration, the last two being the most common.

If greater than 50% pain relief is achieved over the trial period (about a week), the patient is a suitable candidate and they return for removal of the temporary percutaneous lead and scheduled for a permanent device. If a permanent lead has been implanted for the trial, they return for generator implantation. The generator is implanted in a separate pocket created by blunt dissection at a depth of about 1 cm. The small size of the newer generators permits implantation in many locations: lateral to the entry site, in the abdomen, chest wall, or upper buttocks. Both regular and rechargeable batteries are available. It is essential that the pocket fits the generator snugly to minimize movement of the implant. The lead is tunneled from the anchor site to meet the pocket, and any excess length is coiled beneath it. Standard surgical techniques are utilized. Postoperative infection usually mandates explantation of the device. Lead migration, the most common complication, usually requires a revision and placement of a paddle lead in the epidural space via laminotomy (Fig. 13.33).

Figure 13.33 Intraoperative film of thoracic paddle lead placement via laminotomy.
Tunneled Epidural
Figure 13.34 Boston Scientific generator and paddle lead. With permission from Boston Scientific, Natick, MA.

Detailed programming of the stimulators takes place in recovery after the procedure. The lead electrode arrays allow for an almost infinite number of stimulation programs varying the amplitude, frequency, pulse width, and contacts used. The programming and charging of the device take place via remote placed next to the skin. There are three main manufacturers of the devices: Medtronic Corporation (Minneapolis, MN; www.medtronic.com), Boston Scientific (Natick, MA; www.bostonscientific.com), and St. Jude Medical - formerly ANS (St. Paul, MN; www.sjm.com). Extensive physician and patient information can be found on the web sites listed (Figs. 13.34 and 13.35).

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