Spinal Cord Stimulation

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Chapter 15 Spinal Cord Stimulation

Chul-Joong Lee, MD, PhD, Sang-Chul Lee, MD, PhD, Yong-Chul Kim, MD, PhD

Spinal cord stimulation (SCS) has been used for a wide variety of conditions (see later discussion of indications). The procedure is effective in patients who have chronic intractable pain of the trunk or limbs. Neuropathic pain responds well to SCS, whereas the procedure is usually ineffective in treating nociceptive pain and central pain. SCS has been used with increasing effectiveness because of improvements in patient selection criteria, lead placement accuracy, and devices (multipolar and multichannel). Studies have now shown that SCS is cost effective in comparison with conventional medical management, especially in the treatment of failed back surgery syndrome [1]. Kumar and associates [1], who conducted a 22-year study, reported effective long-term pain control, with a mean follow-up of 97.6 months, in 59.3% of all patients screened and 74.1% of the 328 patients in whom the hardware systems were internalized.

Treatment objectives

To reduce rather than eliminate pain and diminish the use of opioids; 60% to 70% of patients may experience a 50% to 70% reduction in pain.

To improve generalized well-being.

To improve activity levels and degree of disability and to encourage greater independence.

To improve the psychiatric symptoms, such as depression and anxiety, that frequently accompany chronic pain.

Indications

General considerations in the selection of SCS for a particular patient are as follows:

More conservative therapies have failed.

Pathology is the basis for the pain complaint.

Further surgical intervention is not indicated.

There is no serious untreated drug dependence problem.

Psychological clearance has been obtained.

There are no contraindications to implantation.

Trial screening has been successful.

The patient is able and willing to use the therapy.

The patient understands the limits and risks of the therapy.

Special indications for this procedure include the following:

Vascular pain: refractory angina and peripheral vascular disease

Failed back surgery syndrome

Spinal stenosis, nerve-root avulsion

Complex regional pain syndrome type I or II

Postherpetic neuralgia

Phantom pain and stump pain

Arachnoiditis

Urologic diseases, such as interstitial cystitis and urge- incontinence

Neuropathic perineal pain

Preoperative preparation

All patients should be screened by a psychologist before the trial implantation. Psychological screening includes the Minnesota Multiphasic Personality Inventory (MMPI) and a structured interview (past medical history, education, employment history, personal relationships, prior medical treatment, medication history, coping strategies, activity level, and pain severity). Patients who are approved for SCS should be educated about the system, its use, and the trial and implant procedures by means of printed materials or a video.

Radiologic anatomy

Figure 15-1 shows examples of the radiographic films that should be obtained in order to evaluate the following aspects of the thoracolumbar spine:

Interlaminar space: to identify and mark vertebral segments for needle and lead placement

Spinous process: to predict vertebral body rotation and place the lead on exact site

Intervertebral foramen: to place the lead on the posterior epidural space

Figure 15–1 Anteroposterior (A) and lateral (B) images of the thoracolumbar spine.

Instrumentation

The following instruments and equipment are needed for a trial of SCS :

Local anesthetics and antibiotics

25-gauge infiltration needle

Syringes for infiltration of local anesthetics

Figure 15–2 Tuohy needle (left) and guidewire (right).

Figure 15–3 Various types of leads for spinal cord stimulation.

Figure 15–4 Various types of anchors. (A) twist-lock, (B) three-wing (C) two-wing (D) EZ

Figure 15–5 Two kinds of tunneling tools. Top, A tunneling tool with a passing straw for trial stimulation. Bottom, An extension passer with an obturator for implantation of the pulse generator.

Figure 15–6 Various tools for percutaneous extension. A, Percutaneous extensions with or without plastic handle; B, wrenches; C, silicone boot.

Figure 15–7 Screeners (A) and screening cables (B). Item on left side of each figure is that for trial stimulation and item on right side of each figure is that for pulse generator implantation (all manufactured by Medtronic, Inc, Minneapolis, MN).

The equipments for implantation of pulse generator are as follows:

Local anesthetics and antibiotics

25-gauge infiltration needle

Syringes for infiltration of local anesthetics

Minor suture set

Figure 15–8 Pulse generators. (all manufactured by Medtronic, Inc, Minneapolis, MN)

Figure 15–9 Patient programmers for pulse generators. (all manufactured by Medtronic, Inc, Minneapolis, MN)

Procedure

Implantation of the Trial Lead

Preparation for Implantation of the Trial Lead

1. The patient’s written informed consent is obtained.

1. Place the patient in the prone position.

2. Place a pillow under the patient’s abdomen or chest to promote adequate forward flexion of the spine and to facilitate epidural lead placement.

3. Identify and mark vertebral segments for needle and lead placement (Table 15.1).

4. Place the radiopaque pointer over the epidural entry location (just lateral to midline) at the target intervertebral space (Fig. 15-10); then mark this location on the patient’s skin with a sterile marker.

5. To mark the needle entry site, place a pointer on the pedicles, checking the location of the pedicles with a fluoroscope (Fig. 15-11). To improve accuracy during this procedure, use an anteroposterior (AP) C-arm (fluoroscope) image.

6. Place the pointer along the trajectory line connecting the skin entry mark with the epidural entry mark (Fig. 15-12).

7. Anesthetize the needle entry site and needle trajectory with 1% lidocaine (Fig. 15-13).

8. Needle entry should be made into the epidural space using a paramedian approach and with AP projection of the C-arm. Insert the Tuohy needle (Fig. 15-2) until it touches the middle lamina, somewhat lateral to the spinous process of the vertebra, and advance the needle to the superior edge of the lamina while keeping it in contact with the bone.

9. Rotate the C-arm to a lateral projection, and carefully advance the needle into the epidural space using a loss-of-resistance technique with a loss-of-resistance syringe. The needle should be inserted at a shallower angle, less than 30 degrees with the skin, and the beveled edge should be facing cephalad (Fig. 15-14) to avoid puncturing the dura and to make it easy to insert the lead into the epidural space.

Table 15.1 Pain Location, Lead Tip Level, and Entry Level for Spinal Cord Stimulation

Pain Location	Lead Tip Level	Entry level
Foot only	T11-L1 (L1)	L2-L3
Anterior thigh	T11-T12	L2-L3
Posterior thigh	T11-L1	L2-L3
Perineum	T11-L1 (midline)	L2-L3
Buttock and lower extremity	T9-T10 (T11-L1)	T12-L1
Lower back	T9-T10 (midline)	T12-L1
Upper chest wall	T1-T2	T4-T6
Upper extremity	C3-C5	T1-T3
Hand	C5-C6	T1-T3
Shoulder	C2-C4	T1-T3
Neck	C1-C2	T1-T3
Jaw	C2	T1-T3

Data from Medtronic, Inc: Spinal Cord Stimulation—Percutaneous Lead Implantation Guide. (NI-2772EN, UC9604345aEN) Minneapolis, MN, Medtronic Inc, 1999, p 11; and Barolat G, Massaro F, He J, et al. Mapping of the sensory responses to epidural stimulation of the intraspinal neural structures in man. J Neurosurg 1993;78:233-239.

Figure 15–10 Placing the pointer at the epidural entry location (T2-T3 disc level at skin surface (A) and AP fluoroscopic view (B), L2-L3 disc level at skin surface (C) and AP view (D). If two leads are inserted, the second lead can be inserted at the contralateral side of the same level or at the ipsilateral side one level above or below the first lead.

Figure 15–11 Placing the pointer at the needle skin entry site. Right T4 pedicle at skin surface (A) and AP fluoroscopic view (B), right L4 pedicle at skin surface (C) and AP view (D).

Figure 15–12 Placing the pointer along the expected needle trajectory. From T2-T3 disc level at skin surface (A) and AP fluoroscopic view (B), from L2-L3 disc level at skin surface (C) and AP view (D).

Figure 15–13 Using the 26-gauge needle to anesthetize. From T2-T3 disc level at skin surface (A) and AP fluoroscopic view (B), from L2-L3 disc level at skin surface (C) and AP view (D).

Figure 15–14 Needle insertion angle. From right T4 pedicle level at skin surface (A) and from right L4 pedicle level at skin surface (B).

Before insertion of the needle, we prefer to make a 3- to 5-cm longitudinal skin incision along the needle entry site with a small subcutaneous pocket to hold the anchor, extra lead, and extension. This maneuver reduces the chance of infection and allows for easy control of bleeding at the pocket site.

Initial Lead Placement

1. Under fluoroscopic guidance, slowly insert the guidewire (Figs. 15-2 and 15-15) to confirm the position of the needle and to predict the early-phase direction of a trial screening lead (Fig. 15-3). Then insert the lead through the needle after removal of the guidewire (Fig. 15-16).

2. Before advancing the lead, rotate the bevel of the needle so that the lead tip is facing the desired direction. If there is difficulty in advancing the lead, do not force it, because doing so could cause dural puncture or problems with the lead.

3. Carefully advance the lead to the initial target placement site (1-2 upper vertebral levels above the expected target stimulation site). To make advancing the lead easier, pinch it between two fingers close to the needle hub. If the lead does not go to the target or if it goes too laterally, try advancing the lead after bending the tip of the lead’s stylet to some degree; this step can make handling the direction of the lead easier.

4. Repeat the preceding steps if a second lead is required (Fig. 15-17). When another lead is needed, the epidural needle can be inserted at a different level or at the same level.

5. Under the fluoroscopic guidance, maintain lead position and carefully replace the stylet with the short stylet for intraoperative test stimulation.

Figure 15–15 Guidewire through the needle. Right T4 pedicle at skin surface (A) and AP fluoroscopic view (B), right L4 pedicle at skin surface (C) and AP view (D).

Figure 15–16 Advance the lead through the needle. Right T4 pedicle at skin surface (A) and AP fluoroscopic view (B), right L4 pedicle at skin surface (C) and AP view (D).

Figure 15–17 Two leads in the epidural space. Leads between T10 and 12 at AP view (A) and lateral view (B).

Intraoperative Test Stimulation (Fig. 15-18)

1. Connect the cylindrical twist connector of the screening cable (Fig. 15-7) and lead stylet handle (Fig. 15-3).

2. Set the amplitude of the screener (Fig. 15-7) to 0 V, the pulse width to 240 microseconds, and the rate to 30 Hz. To minimize the patient’s discomfort, turn the screener off before connecting and disconnecting the screening cable and changing electrode settings.

3. Select one positive and one negative lead (bipolar), and turn the screener on. Test different electrode combinations and polarities by changing the appropriate controls on the screener. The four electrodes of the lead are numbered 0, 1, 2, and 3 from the tip of the lead. For a dual-lead system, the second lead’s electrodes are numbered 4, 5, 6, and 7.

Figure 15–18 Lead connected to screener for test stimulation.

Ideally, the active electrodes are positioned at the center of the electrode array (e.g. off, –, +, off.). This arrangement ensures that if lead migration happens, effective stimulation could be possible through reprogramming instead of surgical repositioning. Reduce the amplitude to zero volts before changing any electrode polarity.

4. Increase the amplitude to the point at which the patient first begins to feel tingling.

5. Increase the amplitude until the patient’s pain or motor effect threshold is reached.

6. Reduce the amplitude to the point at which the patient feels comfortable, yet strong, paresthesia.

7. Make micro-adjustments in lead position until the optimal position is located.

8. Save the AP and lateral fluoroscopic images (Fig. 15-19) that show the final lead position as a reference for the rest of the procedure.

9. When testing is complete, disconnect the cable and carefully remove the short stylet of the lead.

Figure 15–19 The anteroposterior and lateral fluoroscopic images of the final lead position. (cervical level (A, B) and lower thoracic level (C, D).

Completion of Trial Procedure

1. Prepare to remove the needle while watching the fluoroscopic image to ensure that the lead position does not change. Make a 3- to 5-cm longitudinal incision along the entry site before removing the needle, if this incision was not made before the needle was inserted. Grasp the lead body outside the needle hub, and gently pull the needle. Slowly pull the needle back until the lead is exposed beyond the tip of the needle.

2. Repeat the preceding step for removal of the second needle if a dual-lead system is being used. If there is any concern about whether the lead position has changed, check the paresthesia pattern again.

3. Make a small subcutaneous pocket for the anchor, extra lead, and extension if this was not done prior to needle insertion. We prefer to make the incision and the pocket before insertion of the Tuohy needle.

4. Slip the anchor down into the incision. Suture and fix the anchor with a nonabsorbable suture (Fig. 15-20).

5. Make a small incision for the exit of the extension cable in the flank below the twelfth rib.

6. Make a tunnel using a tunneling tool with a passing straw (Fig. 15-5) between the pocket and the extension exit site and pull the extensions through the passing straw (Fig. 15-21).

7. Pass the silicone boot (Fig. 15-6C) down the lead body, and use the wrench to tighten all four setscrews in the extension connector (Fig. 15-6B). Do not over-tighten the setscrews.

8. Push the boot over the extension connector, and tie one suture around the wide end of the boot for stabilization.

9. Check the integrity of the system again using the screener.

10. Close the midline incision, and apply occlusive dressing.

Figure 15–20 Anchoring the lead.

Figure 15–21 Tunneling (A), tightening the setscrews (B), subcutaneous positioning (C) and closing the midline incision (D).

Implantation of the Pulse Generator

1. Carefully open the subcutaneous pocket made previously to hold the anchor, extra lead, and extension, taking care to avoid accidentally cutting the lead (Fig. 15-22A and B). Then unbind the screws and lead (Figs. 15-22C and D).

2. Test the lead function thoroughly.

3. Identify the tunneling route between the lead incision and the abdominal pocket site, and mark it on the skin (Fig. 15-24).

Figure 15–22 A and B, Opening the subcutaneous pocket made previously to hold the anchor, extra lead and extension, with care taken to avoid accidentally cutting the lead. C and D, Unbinding the screws and lead.

Figure 15–24 Drawing the subclavicular pocket site and subcutaneous tunneling tract (Before) and after the pulse generator implantation (After). C, clavicle; H, humerus head; P, pocket site for pulse generator.

We prefer to place the pocket site for lower extremity stimulation at the upper abdominal wall rather than back below the iliac crest (Fig. 15-23). Placement of the pulse generator (Fig. 15-8) in the buttock region may produce up to a fivefold higher tensile loading than placement in the abdomen or subclavicular area (Fig. 15-24).

Figure 15–23 Drawing of the incision for the pulse generator pocket in relation to the ileogastric nerve, the cluneal nerves, and the iliac crest. The incision avoids cutting through the superior cluneal nerves medially and the lateral cutaneous branch of the ileogastric nerve laterally, thus preventing potential postoperative pain or dysesthesia in the buttock or groin, respectively. An arched 7.5-cm incision is recommended in the superior outer quadrant of the buttock, 14 cm from the midline, and 2 cm inferior and parallel to the inferior rim of the posterior superior iliac crest.

(From Andaluz N, Taha JM. Implantation of the synergy pulse generator in the gluteal area: Surgical technique. Neuromodulation. 2002;5:72-74.)

We prefer to place the pocket site for upper extremity stimulation at the subclavicular area, because when the pulse generator is implanted at the abdomen, patients may complain of discomfort during movement and because lead migration occurs frequently owing to long distance from the anchor to the pulse generator (Fig. 15-20).

4. Make an incision at the pocket site (upper abdominal wall, subclavicular, or lower back below the iliac crest) (Fig. 15-25A).

5. Create a subcutaneous pocket using a blunt finger dissection technique. The depth of the pocket should be no more than 1 to 1.5 cm (Fig. 15-25B).

6. Introduce the extension passer with an obturator (Fig. 15-5) subcutaneously from the spine incision to the pocket site, and insert the connector end into the obturator end (Fig. 15-26; Fig. 15-5; see also Fig. 16-20 for the one-step tunneling technique).

Figure 15–25 Creating a subcutaneous pocket with a linear incision (A) and blunt finger dissection (B).

Figure 15–26 Tunneling and the fixation of the extension connectors with the extensions. A, The extension passer is bent to conform to the patient’s contour and tunneled at the subcutaneous level from a small flank incision to the pocket. The obturator is removed from the extension passer by unlocking the obturator tab from the extension passer handle, the extension carrier is inserted into the extension passer, and the extensions are attached at the lead carrier. B, The extension carrier is locked at the extension passer handle, and the extensions are carefully pulled through the subcutaneous tunnel to the flank incision. C, Then tunneling from the spine site to the flank incision is performed with the same technique. The extension must be protected from the tunneling tool on the second pass. D, Two pulse generator connectors of the extension can be seen at the pocket site. E, Each setscrew on the connector block is tightened. F, Sutures are made around each end of the boot.

A two-step tunneling technique, from flank incision to the pocket site (Fig. 15-26) and then from the spine incision to the flank incision (Fig. 15-26C), is required in some cases.

7. Pass the silicone boot down the lead body, and use the wrench to tighten all four setscrews in the extension connector (Figs. 15-6B and 15-26E). Do not over-tighten the setscrews.

8. Push the boot over the extension connector, and suture around each end of the boot with nonabsorbable sutures (Fig. 15-26F).

9. Insert the pulse generator into the prepared pocket with the lettered side facing outward. Carefully coiling the excess extension under the pulse generator is advisable (Fig. 15-27).

10. Close and dress the incision.

Figure 15–27 Implantation of the pulse generator. A, The extension connector pins are inserted into the connector block of the pulse generator, and each setscrew on the connector block is tightened with a wrench. B, Assembled pulse generator. C and D, Fixation of the pulse generator with two nonabsorbable sutures onto the fascia. E, Insertion of the pulse generator into the pocket with the lettered side facing the skin. F, Positioning of the screener over the pulse generator site to test system function.

Avoiding Complications

Precautions that the operator should make to minimize the risk of technical complications after implantation are as follows [5]:

Leads should be introduced via a paramedian rather than a midline approach. A shallower angle of introduction is beneficial for lead steering and helps minimize the potential for compression of neural structures due to bending of the relatively stiff lead.

Use fingers or a rubber-tipped forceps when handling the lead.

Be extremely careful with sharp instruments around the lead.

Do not force the lead up the epidural space. Use the guidewire packaged in the lead kit to clear a path for the lead.

Do not tie a suture directly to the lead body.

Introduce the lead as close as possible to the midline.

Bends or curves in the lead may have a tendency to straighten, potentially leading to migration.

Injection of fluid or air into the epidural space should be discouraged, because the fluid or air decreases friction and may promote lateral migration of the lead.

Attach the anchor to the lead with silicone nonabsorbable suture.

Attach the anchor to the lumbodorsal fascia with a figure-of-eight suture to minimize tissue trauma.

Push the tip of the anchor through the fascia in order to maximize the bend radius of the lead with flexion and extension of the spine.

For implantation, position the patient with the spine in neutral to minimize extremes of flexion and extension.

Place the anchor as near as possible to the spinous process to avoid lead movement generated by muscle contractions.

Avoid bending or kinking the lead. If there is any excess lead body, create gently coiled loops of no less than 2 cm in diameter.

Avoid placing tension on the lead during surgery. Leave the lead body as loose as possible after connecting the extension, to avoid unnecessary tension on the lead.

Placement of the pulse generator in the buttock region may produce up to fivefold higher tensile loading compared with placement in the abdomen or subclavicular area. Therefore, buttock pulse generator placement is reserved for special clinical situations and should not be performed routinely.

If any system component becomes damaged during implantation, remove it and replace it with another component for permanent system implantation.

See Fig. 15-28 concerning lead fractures.

Figure 15–28 Report of lead fracture.

Postprocedural management

Effects of Body Position on Stimulation

Stimulation can feel different as changes in body position occur; the operator should take the following actions when stimulation changes:

Stimulation increases when the head is bent back or the patient is leaning back, lying down, or sitting; the amplitude should be decreased.

Stimulation decreases when the patient is standing up; the amplitude should be increased.

Stimulation stops when the neck is bent forward or twisted but resumes suddenly when the patient assumes a different position; the screener should be turned off or the amplitude down when the patient is changing position or making adjustments until the patient becomes accustomed to the stimulation changes that occur.

Discharging the Patient

The patient can be discharged on the first postoperative day if there are no postoperative complications.

Case study 15.1

A 32-year-old man presented with left arm pain. He had had a traffic accident 11 months before visiting our pain center. At that time, he sustained a ligament injury caused by left wrist hyperextension. He had complained of a tingling sensation and hyperesthesia on left first, fourth, and fifth fingers. Three months before visiting our pain center, an arthroscopic operation was performed at the left wrist. Two weeks after the operation, intermittent rigidity and burning sensation appeared on the left arm.

Findings of cervical magnetic resonance imaging, electromyography with nerve conduction study, and bone scan were nonspecific. Digital infrared thermographic imaging of the upper extremities showed significant difference of temperature between the two arms (Fig. 15-29).

Figure 15–29 Case Study 15.1: Digital infrared thermographic findings in the upper extremities of before (Left) and after (Right) the thoracic sympathetic ganglion block performed at the left T3 level.

The patient was treated with various medications (gabapentin, triazolam, carbamazepine, fluoxetine, and baclofen) as well as interventional pain treatments (cervical epidural steroid injection, ketamine infusion therapy, pulsed radiofrequency lesioning at the cervical dorsal root ganglia, thoracic sympathetic ganglion block [Fig. 15-29], and alcohol neurolysis) without significant pain relief (visual analog scale [VAS] for pain score 9/10).

A trial of spinal cord stimulation was performed, and the lead tip was located at the upper end plate of C4 (Fig. 15-30). Paresthesia totally covered the patient’s pain area. He reported significant alleviation of the pain (VAS score 3/10) during the trial period. After 1 week of trial stimulation, the implantation of a pulse generator was performed.

Figure 15–30 Case Study 15.1: Anteroposterior (left) and lateral (right) radiographs after implantation of a pulse generator.

Case study 15.2

A 23-year-old man presented with left lower leg pain (9/10 on a VAS) below the knee (Fig. 15-31). He had received minor trauma at the left ankle from a fall 5 months before his visit to our pain center. He had received medications and nerve blocks, including lumbar sympathetic plexus block, at other hospitals without alleviation of pain. He was diagnosed with complex regional pain syndrome type I (Fig. 15-32A) and underwent implantation of a spinal cord stimulation pulse generator. Trial stimulation using a single lead was performed. The skin entry site was at the L1-L2 level, and the lead tip was located at the T11 level, which produced concordant paresthesia at the painful area.