Female Pelvic Surgery

4. Sacral Neuromodulation

Kimberly L. Burgess  and Steven W. Siegel 

(1)

Division of Urology, Department of Surgery, Greenville Health System, Greenville, SC, USA

(2)

Metro Urology, Center for Female Urology and Continence Care, Woodbury, MN, USA

Kimberly L. Burgess

Email: Kburgess2@ghs.org

Steven W. Siegel (Corresponding author)

Email: pnedoc@comcast.net

Email: siegel.steven@gmail.com

Background

Millions of men and women throughout the world are bothered by urinary incontinence and voiding dysfunction. A recent economic study estimated the disease specific costs of overactive bladder (OAB) in the United States to be $24.9 billion affecting approximately 18.6 % or 42.2 million adults [1]. First and second line treatments include behavioral therapies, dietary changes, pelvic floor muscle training, and anti-muscarinic medications. A significant number of patients discontinue medical therapy secondary to side effects or costs. In a large study of the California Medicaid population, Yu et al. found that only 10 % of patients continued taking a prescription medication for management of their OAB after 1 year, with the median time to discontinuation of 50 days [2]. After initial therapies have failed, either secondary to suboptimal control of symptoms, or poor toleration by patients, other treatment options such as sacral neuromodulation (SNM) should be considered in appropriate patients as recommended in the AUA guidelines [3]. This chapter describes indications for use, patient evaluation, surgical techniques, and outcomes for sacral neuromodulation and percutaneous tibial nerve stimulation (PTNS).

Sacral Neuromodulation Mechanism of Action

SNM is proposed to exert its affects through different mechanisms of action. Neural pathways exist that result in amplification, coordination, and timing that are needed for normal micturition [4]. The micturition reflex is initiated through signaling to the brain that the bladder is full from bladder afferent nerves, which are composed of myelinated Aδ fibers and unmyelinated C fibers [4]. The brain then sends signals through spinal pathways to turn off the guarding reflex, relax the external sphincter, and contract the detrusor, resulting in voluntary voiding of urine [5]. Bladder overactivity and voiding dysfunction are likely the result of an imbalance of the reflexes between the bladder, pelvic floor, and urethral sphincter. SNM appears to restore this balance that is needed for normal voiding function. One possible explanation is that SNM exerts its effect by stimulating afferent axons in the spinal roots modulating the reflex pathways. Areas where SNM may affect micturition include:

·               Inhibition of post-ganglionic nerve terminals

·               Presynaptic inhibition of primary afferents

·               Affecting pudendal afferents that transmit somatic and visceral neurochemical signaling

·               Inhibition of spinal tract neurons involved in micturition reflex

·               Suppression of guarding reflexes through turning off bladder afferent input to internal sphincter or external sphincter interneurons

·               Activation of bladder efferents to stimulate voiding while simultaneously turning off excitatory pathway to urethra [5].

In the case of OAB, bladder preganglionic neurons or interneuronal transmission may be inhibited in the afferent micturition reflex. In the case of incomplete emptying, SNM may improve non-obstructive urinary retention through suppression of guarding reflexes [45].

Initial work demonstrating the possible clinical value of SNM was conducted by Tanagho and Schmidt. The therapy, commercially marketed as InterStim™ (Medtronic, Inc., Minneapolis, MN), was first approved by the US Food and Drug Administration (FDA) for treatment of urinary urge incontinence in 1997 followed by approval for treatment of urinary urgency, urinary frequency, and non-obstructive urinary retention in 1999. More recently in 2011, SNM was also approved for fecal incontinence [6].

Over time, SNM has evolved with technological improvements, including the development of the percutaneous tined lead, decreased size of the implantable neurostimulator (INS), and use of fluoroscopy during office stimulation procedures (percutaneous nerve evaluation or PNE). Initial non-tined leads required fascial or bone anchoring, resulting in the need for larger incisions and general anesthesia for placement. In 2002, the tined lead, initially described by Spinelli et al. [7], was FDA approved allowing for placement under conscious sedation combined with local anesthesia, which increased the ability to use patient sensory information during chronic lead placement [8]. Anchoring within the surrounding subcutaneous tissue and muscle is accomplished with four sets of tines proximal to the electrodes decreasing the possibility of lead migration [7]. A recent publication reporting long-term outcomes for SNM found the revision rate decreased from 50 to 31 % using the tined lead [9]. The rate of revision noted in the InSite Study was 12.9 % in the first year after implantation of the device [10]. In 2006, the InterStim II INS was introduced, which is 50 % smaller than the previous model, resulting in less discomfort and improved patient acceptance. However, this change was made at the expense of a shorter average battery life (3–5 years compared to 7–10 years) [8]. The use of fluoroscopy during PNE allows for improved temporary lead placement, potentially resulting in a greater sensitivity of the office trial, decreasing the need for a staged procedure performed in the operating room [7].

Evaluation/Work-Up

Indications and Patient Selection

Overactive Bladder

The International Continence Society defines OAB as “urgency with or without urge incontinence usually with frequency and nocturia in the absence of an underlying metabolic or pathological condition [11].” Patients should be evaluated with a thorough history and physical exam to evaluate their voiding complaints. In history taking, one may identify that voiding symptoms developed after an inciting event such as pelvic surgery, trauma, or back injury. During the history and physical exam, patients should be evaluated for possible neurologic causes of their symptoms. During pelvic exam, the patient should be evaluated for evidence of pelvic floor muscle dysfunction as a cause of their symptoms, which can be managed successfully with pelvic floor physical therapy. It is important to evaluate for incomplete bladder emptying by obtaining a post-void residual, and also to rule out urinary tract infection as the source of symptoms with a urinalysis and possible urine culture. A cystoscopy should be considered if patient has risk factors for bladder pathology such as, but not limited to, hematuria, tobacco use, or prior pelvic surgery. Urodynamic evaluation (UDS) should be considered, especially in patients with mixed incontinence, evidence of incomplete bladder emptying, or in patients with possible neurologic causes of their voiding complaints. A UDS may or may not show uninhibited detrusor contractions [5]. A voiding diary documenting number of daily voids, episodes of urgency, episodes of incontinence, voided volume, and fluid intake should be obtained. This information is paramount in not only demonstrating severity of voiding dysfunction but also gives a baseline to compare to the posttreatment voiding diary to assess for objective improvement. Patients with symptoms of an overactive bladder that have not had successful management with conservative therapies are candidates for SNM. Success of SNM in patients with OAB is reported at 59–85 % with average follow-up ranging from 29 months to 5 years [91214].

Non-obstructive Urinary Retention

Patients with urinary retention or incomplete bladder emptying must be evaluated for obstructive causes, which can be evaluated with a UDS. A voiding diary should be completed prior to test stimulation that includes daily number of catheterizations, voided volume, and catheterized volume. A repeat voiding diary should then be obtained during the test stimulation phase to determine success. SNM is not indicated in patients with evidence of an obstructive etiology of their voiding complaints. Success (defined as minimum of 50 % decrease in catheterized volumes and number of daily catheterizations) at 18 months is reported at 70–83 % [1415] with longer follow-up ranging from mean of 51 months to 5 years showing success in 71–88 % of patients [913].

Pelvic Pain/Bladder Pain Syndrome

Pelvic pain and bladder pain syndrome are currently not FDA approved indications for SNM; however, patients with these conditions often have coexisting voiding complaints such as urinary urgency or frequency, which would make them candidates for this therapy. As discussed above, it is important to evaluate for pelvic floor muscle dysfunction on physical exam as pelvic floor physical therapy should be considered as an initial therapy when appropriate. In patients where conservative therapies have failed, a trial of SNM is an excellent potential option. Studies have shown the therapy to provide some benefit in patients with bladder pain syndrome and pelvic pain. However, it is important to educate the patient that their pain may not improve with SNM. One of the treatment’s potential benefits is that a minimal risk trial is conducted to assess how the therapy will affect their symptoms. Multiple studies have shown that SNM results in improvement of pain parameters, with long-term success ranging from 60 to 77 % with median follow-up of 19–61.5 months [1618]. Gajewski and Al-Zahrani found that the presence of urgency at baseline was a positive predictor of long-term success [17]. One study found that patients with bladder pain syndrome required more programming visits [19] following implant, while another group found that the rate of explant was highest in the bladder pain syndrome patients compared to those with OAB or urinary retention [9]. A study of patients with refractory interstitial cystitis showed a 36 % reduction in the mean dose of daily opiate use after implant compared to baseline, with 22 % of patients able to stop their use completely [20].

Other Indications

Fecal incontinence can be a devastating symptom, affecting 1–2 % of the population [21]. Initial management includes dietary changes, biofeedback, and medical therapy. The FDA has also approved the use of SNM for patients with chronic fecal incontinence. One-, two-, and three-year therapeutic success is reported at 83 %, 85 %, and 86 %, respectively, with complete continence in 40 % of patients at 3-year follow-up. Success was defined as at least a 50 % reduction of incontinent episodes per week compared with baseline and to be included in the study; patients were required to have more than two incontinent episodes per week on average and symptoms present greater than 6 months [2122]. This specific indication for the use of SNM will be discussed further in Chap. 16.

Another indication for SNM, although not FDA approved, is childhood dysfunctional elimination syndrome that is refractory to medical management and behavioral therapies. At median follow-up of 27 months, one group reported improvement or resolution of incontinence, urgency, frequency, nocturnal enuresis, and constipation in 88 %, 69 %, 89 %, 69 %, and 71 %, respectively [23].

Procedures

Two different types of trials exist for patients to undergo test stimulation with SNM, including the PNE and staged lead implantation. A PNE involves placement of a temporary monopolar lead that is removed at the end of a 3–10 day trial period. Advantages to the PNE are that it can be performed in the office with local anesthesia, and there is easy removal of the temporary leads. A disadvantage is the potential for migration of the leads, thereby decreasing the accuracy of the trial in determining whether a patient will benefit from the therapy. During the staged trial, a quadripolar tined lead is positioned as the first stage with placement of the INS as a second stage if successful. The advantages of a staged trial are decreased risk of lead migration, increased programming options during the trial due to the lead configuration, and ability for a longer test period. A disadvantage of the staged procedure is the need for two procedures using monitored anesthesia care (MAC) in the operating room. One’s choice to perform a PNE versus a staged procedure may depend on the patient and the surgeon’s access to equipment. A PNE may be performed using fluoroscopy, which is the author’s preference, or using anatomic landmarks to determine placement of the temporary leads. One may prefer to perform staged procedures if access to fluoroscopy is not available in the office. The author uses both types of test stimulation based on the patient’s preference and condition, and both techniques will be described. Since “frequent” fecal incontinence may only happen once per week, a staged trial has been thought to be more likely to capture the benefit, though we have often noted changes during a PNE trial.

Percutaneous Nerve Evaluation

Patient Positioning and Preparation

Prior to the procedure, the patient should complete a baseline voiding diary that documents their specific voiding complaints and any incontinence if present. Diaries should include the intake volume, frequency of urination, volume voided, degree of urgency, number and severity of incontinent episodes, and type and number of pads used. If the patient establishes their baseline diaries using anticholinergic mediations, the trial is also conducted using the medication, since the intention is to measure the effect of only one variable. If the patient has urinary retention, they should also record the number of daily catheterizations and catheterized volumes. If the trial is being conducted for fecal incontinence, details of these episodes along with consistency of stool and number of daily bowel movements should also be recorded. It is important to discuss the procedure with the patient, so they know what to expect during the procedure and help reduce patient anxiety since it will be performed without sedation.

The patient is placed on a table that will accommodate the fluoroscopic c-arm in the prone position with pillows placed under the patient’s head, hips, and shins. It is important to insure that the patient’s hips are positioned where the c-arm unit can be passed under the table to allow for viewing of the sacrum during the procedure. The buttocks and feet need to be uncovered to watch for motor responses during the procedure. The patient’s lower back and buttocks are prepped with an antiseptic solution and the operative field is draped with towels and/or small adhesive drapes provided in the Test Stimulation Lead Kit (Medtronic, Minneapolis, MN) (Fig. 4.1a, b). A grounding pad is placed on the patient’s heel or foot if there is deep callous, and the red connector of the Test Stimulation Cable is connected to the grounding pad. The black connector of the Test Stimulation Cable is attached to the Patient Cable. The Test Stimulation Cable is attached to the test stimulation box (Fig. 4.2).

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Fig. 4.1

PNE components. (a) Prep kit which includes drapes and prepping materials. (b) Test stimulation kit: foramen needles, syringe, and needle for local anesthetic, test stimulation lead, marking pen, hemostat, and forceps

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Fig. 4.2

The grounding pad is attached to the patient’s foot with the red connector of the Test Stimulation Cable attached. The black connector of the Test Stimulation Cable is attached to the Patient Cable and the Test Stimulation Cable is attached to the test stimulation box as shown

Selecting the Appropriate Foramen Using Fluoroscopy

S3 is the ideal target for lead placement and we attempt to place bilateral leads at this level during the PNE. Rarely, S4 is adequate or preferable, but S2 is not appropriate for chronic stimulation due to the activation of lower extremity motor efferents. Fluoroscopy is used to visualize the sacrum in an anteroposterior (AP) view to identify the medial edge of the sacral foramen on one side, which is marked on the skin with a marking pen (Fig. 4.3a, b). The contralateral foramen location can be approximated by moving two fingerbreadths over and once verified with fluoroscopy, the skin is marked. The skin may be marked or one can visualize an imaginary vertical line parallel to the spine at the medial edge of the foramen to help stay lined up when accessing the foramen from a superior point on the skin. A cross-table fluoroscopic view is then obtained to locate the S3 foramen laterally. Only a few minutes total is spent using the AP projection, with the major portion of the procedure performed in the lateral view. S2 is readily identified as the point where the sacroiliac joint fuses, forming a characteristic shadow. The first anterior protrusion or “hillock” from the anterior surface of the sacrum below this shadow is typically S3. In order to determine the skin entry point of the foramen needle, the skin is marked with a hemostat while looking at skin surface and the sacrum together in a lateral plane (Fig. 4.4). The point of entry is found along the line marking the medial edge of the sacral foramen (previously made while in the AP view), with a line drawn in the mind’s eye starting at the skin mark, paralleling the fusion plain between the sacral vertebra, and targeting a point approximately 1 cm above the S3 hillock. This line is in a cephalocaudal direction at an approximately 60-degree angle. The use of fluoroscopy allows the correct angle to be determined for any body habitus.

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Fig. 4.3

Identifying the medial edge of the sacral foramina using fluoroscopy with (a) showing the clamp on the patient’s skin and (b) showing the AP X-ray

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Fig. 4.4

Identifying S3 on lateral view [24]

Positioning the Needle in the S3 Foramen and Placement of the Temporary Lead

The location of the needle entry point on the skin should be anesthetized with 0.25 % bupivacaine, 1 % lidocaine, or a combination to create a dime-sized wheal. The subcutaneous tissue does not need to be infiltrated with the local anesthetic but the sacral periosteum may require some of the anesthetic if the patient experiences discomfort as the foramen needle touches the bone. Once the bone is touched, a spot lateral fluoroscopy view is obtained to determine if the insertion point is correct, and whether the needle must be aimed in more cephalic or caudal angle. Once the orientation is correct, the needle is “walked” up or down along the line of the medial edge of the foramina until the needle drops off into the foramen (Fig. 4.5). It is important to pull the needle back before changing positions while trying to locate the foramen to avoid torqueing or bending the needle. For larger patients, a 5 in. needle is available. We typically refer to this as “the other” needle in order to minimize patient anxiety.

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Fig. 4.5

Foramen needle placed superior to the hillock of S3

Since the patient is not sedated during the PNE, it can cause discomfort to reposition the needle during the procedure, and we often will keep the initial foramen placement if responses are consistent with positioning along S3. During placement of the tined chronic lead, one should re-direct the foramen needle as needed to get the best positioning along the course of the S3 nerve root. The needle is then stimulated using the patient cable that is attached to the test stimulation device and the patient is observed for sacral root responses (Table 4.1). Responses that correspond to simulation of S3 are bellows (levator contraction resulting in rolling inward and deepening of the intergluteal fold), dorsiflexion of the ipsilateral great toe, and sensation of the stimulation in the genital, perineal, or anal region.

Table 4.1

Sacral root responses

Sacral level

Motor response

Sensory response

S2

Bellows, clamp, dorsiflexion foot, heel rotation, calf cramping

Genital

S3

Bellows, dorsiflexion great toe, dorsiflexion foot

Genital, perineal, anal

S4

Bellows

Anal

If responses are not consistent with S3 and the patient will tolerate further needle manipulation, the skin entry point is re-approximated using lateral fluoroscopy to aim for the next foramen, either above or below the initial point of stimulation. Once appropriate responses are elicited confirming position in S3, the needle stylet is removed and the Test Stimulation Lead (Medtronic) is passed through the needle to the marking on the lead that corresponds to the needle size used (3 or 5 in.). A fluoroscopic image is obtained to gauge the depth of the lead. It is better to err on being slightly deeper rather than too shallow as the lead will likely migrate during the testing period. The foramen needle is removed along with the lead, while maintaining its depth and keeping the stylet in place, and then it is stimulated to assess responses. The PNE lead can be pulled back under fluoroscopy and/or while being stimulated, to gain better positioning. Finally, the lead stylet is removed leaving only the test lead in place. The procedure is then repeated on the contralateral side.

To decrease the potential for lead migration during the testing phase, the author prefers to tunnel the leads using a spinal needle (Fig. 4.6a, b). The leads are then secured in place using a gauze and Tegaderm dressing. Lastly, the leads are attached to Test Stimulation Cables, which are in turn attached to the external stimulation device during sub-chronic stimulation. Patients are then instructed on device use and will complete voiding diaries during a 3–10 day length of trial to evaluate the therapy. During the testing period, they will trial both leads individually. At the end of the trial period, the leads are extracted in the office by removing the dressing and simply pulling gently on each lead. Success is determined through comparing the voiding diary obtained during test stimulation to the baseline diaries, and also by asking the patient subjectively how they feel their symptoms were managed during the trial. If trial is successful, defined as >50 % improvement in symptoms, the patient is offered implantation with placement of the tined lead and INS during a single procedure. If therapy did not result in at least a 50 % improvement in symptoms, the patient can choose to undergo a staged trial, especially if there were any concerns regarding lead migration or lead placement that may have affected the outcome.

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Fig. 4.6

(a) PNE leads after placement. (b) Tunneling of the leads to decrease migration during the trial

Staged Lead Implantation as Initial Trial

Patient Positioning and Preparation

A staged trial involves placement of the tined quadripolar lead connected to a lead extension that is externalized for a prolonged test stimulation trial. As with the PNE and discussed above, the patient must complete a baseline voiding diary prior to the procedure. The procedure is performed with a combination of conscious sedation or MAC with local anesthesia and therefore the patient does require medical clearance to undergo anesthesia. It is preferable to perform the procedure under MAC rather than general anesthesia to allow the patient to give sensory feedback during lead placement. On rare occasion, a patient is not an appropriate candidate for MAC based on other comorbidities and requires general anesthesia. It is important in these situations that the surgeon has good communication with the anesthesia team about the medications given as only a short-acting paralyzing agent should be used to avoid blocking pelvic floor muscle responses during intraoperative stimulation. A preoperative dose of an antibiotic with coverage against skin flora such as cephazolin (Ancef) or vancomycin, if there is concern for MRSA, is administered prior to the procedure. A Hibiclens wash the night before, and morning of surgery, and pre-op skin wipe down with a sage cloth are also measures, which may reduce the potential for infection.

The patient is placed in prone position on a table that will accommodate fluoroscopy with the hips positioned on the table where the c-arm unit will pass beneath the table allowing the surgeon to view the sacrum on both AP and lateral views. Two chest rolls are placed to assist with respiration and pillows are placed under the hips and shins to pad pressure points. The feet remain uncovered to allow observation of motor responses during intraoperative stimulation. The lower back and buttocks are first wiped with alcohol, and then, after drying, prepped with an antiseptic solution such as Dura Prep (3M) solution. After the prepping solution has dried, towels are placed at the bottom of the buttocks, on the sides lateral to where an INS would be positioned, and above the estimated location of L5–S1. An Ioban sheet (3M) is placed smoothly over the entire remaining area of exposed, prepped skin, and the buttocks are gently pulled apart and then released to allow the Ioban to attach/insert itself into the intergluteal fold. Taping apart of the buttocks is not needed in order to see the bellows response, and is discouraged due to the potential for creating patient anxiety and muscle tension. The components of the lead kit are shown in Fig. 4.7. As with the PNE discussed previously, a grounding pad is placed and Test Stimulation Cable and Patient Cable are connected to the external stimulation device (Fig. 4.2).

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Fig. 4.7

Components of lead introducer and lead kits: tunneling device, straight stylet, lead with ball tip stylet in place, directional wire guide, introducer and sheath, two 3 in. foramen needles, torque wrench, plastic covering/boot, and lead extension wire

Selecting the Appropriate Foramen and Positioning the Needle

The process of using fluoroscopy to identify the medial edge of the S3 foramen and identifying S3 on lateral views is the same as described for the PNE. One difference in placement of the tined lead is that only a single lead is placed rather than performing bilateral placement. Either side can be chosen for placement but if the patient has a lateralizing pain component, it is preferred to place the lead on that side. Identifying the skin entry point, administration of local anesthesia to the skin, and placement of the foramen needle is also the same as the PNE. The foramen needle should follow a cephalocaudal path, paralleling the fusion plane between the sacral vertebrae, passing through the sacrum approximately 1 cm superior to the tip of the hillock. The foramen needle is tested only with the tip just anterior to the anterior surface of the sacrum. It is at this point where the “opening threshold” is measured. As opposed to the PNE, it is vital to reposition the needle as necessary to get the most robust responses. We usually aim for this threshold to be at or below 1 V. If it is higher than 2 V, reorientation of the foramen needle is needed, making sure that it is as medial as possible related to the edge of the bone, and also as high as possible related to the hillock. For example, if the tip of the foramen needle is at or below the hillock just as it enters the pelvis, it is nearly always incorrectly placed, and does not need to be tested before repositioning. Also, it is important to note the order in which motor responses are seen at this point. Bellows should come first, and then toe flexion. An opening threshold at or below 1.5 V, with the appropriate pattern of motor and sensory responses, should be obtained before attempting to deploy the tined lead.

Placement of the Introducer Sheath and the Tined Lead

Once the needle has been positioned, a small skin nick is made alongside the needle making sure the needle moves freely within the small incision. The skin nick must be through the skin into fat, and long enough (0.5–1.0 cm) to allow eventual tined lead placement without causing it to be trapped superficially. The inner stylet of the needle is removed and the directional wire guide is passed to the mark corresponding to the needle length (3 or 5 in.). The foramen needle is removed leaving the directional wire guide in place. The lead introducer sheath is then passed over the directional guide under fluoroscopy until the radiopaque marker present at the tip of the sheath is located approximately 1/2–2/3 through the bone table (Fig. 4.8a, b). This step is emphasized as it is critical to the reproducibly successful positioning of the tined lead. Once the sheath has been placed at the proper depth, the introducer stylet and directional guide are removed.

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Fig. 4.8

(a) Lead introducer and sheath in place. (b) Lead introducer in place during a lead revision. Note the different angles of entry and position with respect to the S3 hillock

Prior to passing the lead, the authors suggest exchanging the straight and stiffer stylet, the lead comes packaged with, to the ball-tipped (curved) stylet, which is provided in the lead kit. This is because it is softer than the straight stylet, and allows for attachment to the lead. The lead/stylet assembly becomes more flexible and steerable, allowing it to more precisely approximate the course of the sacral nerve as it enters the pelvis. The lead is passed through the introducer under fluoroscopy with care not to deploy the lead. Accidental deployment can be avoided easily by keeping the introducer tip 1/2–2/3 of the way through the bone table, and making sure that contact points 2 and 3 of the tined lead straddle the bone table. The lead has two marks on the upper half of the lead and if the most proximal (upper) marking passes into the sheath, the lead will be deployed as the tines will be located outside of the sheath. The lead should point slightly caudally and laterally (“down and out”) as it passes anterior to the sacrum. When viewing on a lateral X-ray, one can assess for whether the lead curves outward or laterally by looking at the distance between the lead contact points. The distal contact points (0 and 1) will appear to be spaced closer together in the lateral view if the distal lead points away from its initial entry point anterior to the sacrum (Fig. 4.9a, b). On the AP view (usually taken after final deployment) the proximal contact spacing (between points 3 and 2) should appear closer than the distal (1 and 0) since the lead is coming towards and then moving away from the viewer. If the lead is not pointing in a “down and out” position, it should be repositioned by pulling the lead back under fluoroscopy until the distal tip is within the introducer sheath before adjusting/turning and re-advancing to help pass it along a different path, which can be confirmed on fluoroscopy.

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Fig. 4.9

(a) Deployed lead on lateral view. (b) Deployed lead on AP view

Once positioned, the lead is tested by stimulating at each of the four contact points (0–3) starting at the most distal contact (0) and observing for the threshold at which appropriate responses are first visualized or sensed by the patient. If the response is elicited at a low threshold, this supports that the lead is parallel to the nerve. Ideally, low thresholds should be obtained with stimulation at all four of the contact points, which will allow for longer battery life and maximal programming options. Also, the pattern of responses will help to indicate which way the lead trajectory must be altered. For example, if there is mostly foot response, or foot first and bellows second (favoring S2), the lead course needs to be more downward. If there is all bellows and no toe (favoring S4), the lead must be made to course more upward. If appropriate responses are not seen at a low threshold at each point, the lead should be repositioned as described above. Moving the introducer sheath deeper or shallower within the boney canal changes the “launch point” of the lead, which can help adjust the path the lead takes if needed. The launch point can be retracted simply by pulling back the introducer sheath under fluoroscopic control, but it should only be advanced while the sheath is cannulated by the lead or the introducer stylet and directional guide. It should never be advanced beyond the anterior sacral surface. Even if this happens by mistake, it can interfere with the ideal course of placement due to creating a “false passage.” If after several attempts to reposition the lead, ideal responses are not elicited, it may be necessary to start again with the foramen needle to obtain a different path for the lead. Also, one should consider switching to the contralateral side if unable to get appropriate positioning of the lead. Since the vast majority of patients undergoing lead placement are anatomically and neurologically normal, the main cause for not getting all four contacts yielding appropriate responses at similarly low thresholds is related to technique or lack of persistence, and not patient factors. Once the ideal position is obtained, the tines are deployed by pulling back the introducer sheath under fluoroscopy. During this step, since all four responses are nearly equal, indicating the lead is placed along the nerve, we will slightly advance the lead to the point where contact 3 is just anterior to the bone table. This allows more flexibility in using contact 3 in programming. After final retesting to confirm positioning, the lead stylet should be removed.

Connecting the Lead to the Lead Extension

If the patient is undergoing a full implant following a successful PNE with placement of the lead and INS during a single procedure, this section can be skipped. The authors prefer to place the lead connection at the future site of the INS. To identify this site, the lateral edge of the sacrum is palpated and marked along with the posterior superior iliac crest. The site of the future INS should be marked in a slight diagonal plane overlying an area of fat away from the marked bony landmarks in the upper buttock. Before making the incision, make sure the lead will easily reach this area once tunneled. After administering the local anesthetic to the lateral aspect of the marked incision, a 1–2 cm incision is made through the lateral portion of the marked area extending through the skin into the subcutaneous layer of fat.

The length of the plastic sheath surrounding the provided tunneling device can be used to measure the furthest possible site on the contralateral side of the patient’s back where the lead connection will be externalized. The local anesthetic should be applied to the skin in that area in a quarter sized wheel. The tunneling device is then passed from the incision, through the subcutaneous fat, to the anesthetized area on the contralateral side. It is important that the path of the tunneling device is superior to the sacral incision where the lead was placed. The sharp end of the tunneler is externalized and the metal portion is removed leaving the plastic sheath in place. The distal end of the lead extension is passed through the sheath until it exits the skin and the plastic sheath is then removed. If there is a hang-up while passing the lead extension, the directional guide can be used to help push the extension completely through the tunneling sheath.

Two methods can be used to pass the lead from the sacral incision to the incision in the buttock where it will be connected to the lead extension wire. One method that can be used if the distance is short is using the lead introducer sheath. This technique is more often useful when placing the lead and INS at the same time. The other method is using the tunneling device. The tunneling device may be curved if needed to decrease the amount of excess lead present within the buttock incision. It is important to pass whichever device is chosen deep within the fat so that it does not lie superficially beneath the skin. It is also important that the pre-sacral incision is big enough to allow the tunneling device to be passed without damaging the lead with the tunneling device, or leaving the lead trapped superficially within the incision as mentioned earlier. The lead is in turn connected to the lead extension wire and the four screws are tightened using the provided torque wrench, turning a quarter turn past the click. The plastic covering or boot is placed over the connection hub and secured in place with a prolene tie. A straight clamp is used to grasp gently the plastic sleeve covering the proximal aspect of the lead extension wire, with care taken to avoid damage to the wires, and used to pass the connection along the path of the lead extension until the connection hub lies within the subcutaneous fat just medial to the incision. This allows easy identification of this connection at the time of the completion procedure or during removal. If there is redundant lead present, this should be looped in the subcutaneous fat inferior to the incision so it will not bunch up within the small incision preventing optimal healing and be out of the way when the incision is reopened for the next stage. The wounds are irrigated with antibiotic solution and the subcutaneous fat anterior to the lead and lead extension is closed with 2-0 vicryl suture. The skin of both the buttock incision and pre-sacral incision are closed with a subcuticular 4-0 vicryl suture. Skin glue is placed over both incisions after closure.

Finally, the externalized portion of the lead extension is connected to the lead extension cable, which in turn is to be attached to the test stimulation device for the trial. The connection between the extension and cable is secured to the patient’s back with a Telfa and Tegaderm dressing.

Implantation of the INS (Stage 2)

A completion phase procedure is scheduled 2–4 weeks after the first stage where the INS will be implanted if the trial is successful, or removal of the lead and lead extension if unsuccessful. If there has been significant improvement (>50 %) in the target symptoms based on voiding diary and subjective changes noted by the patient, implantation of the permanent INS is supported. This step is also performed using a combination of MAC and local anesthesia.

Perioperative anesthesia and skin preparation are the same as for the lead implant. The area of the buttock where the prior connecting incision was made is prepped and draped leaving the area where the lead extension wire is externalized outside of the prepped field to decrease contamination. The buttock incision from the first stage is marked and extended medially in the direction of the tunneled lead so that it will be just long enough to accommodate the INS. The skin in this area is infiltrated with the local anesthetic and after incision is made, electrocautery is used to maintain hemostasis. The subcutaneous fat is opened overlying the connection hub. The lead extension wire is cut distal to the plastic sleeve covering adjacent to the connection. The hub is usually left on the lead to protect it until creation of the pocket is complete. The remaining lead extension wire is removed by pulling on the externalized portion, which should be performed by someone outside of the sterile field, usually after the case has been completed and the drapes are being removed.

A subcutaneous pocket is then created using cautery and blunt dissection extending 2–3 cm beneath and parallel to the skin staying anterior to fascia of the muscle. This should be just large enough to allow the INS to be placed assuring that it lies flat and parallel to the skin without excess room to avoid the device “flipping” within the pocket. The prolene tie and plastic boot over the lead connection are cut and removed. The lead is separated from the remaining portion of the lead extension and the wound is irrigated with antibiotic solution. The lead is attached to the INS, which is then placed in the pocket tucking any excess length posterior to the device to prevent lead injury during any future revision surgery that may be needed. The overlying fat should come together without tension if the pocket size is optimal. The subcutaneous tissue is closed with absorbable suture, the skin is closed with a subcuticular absorbable stitch such as Vicryl, and skin glue is placed over the incision.

Initial Device Programming

Following placement of the tined lead, the device is programmed in the postoperative recovery area. It is important to discuss the use of the brown box (placement of lead only) or ICon Patient Programmer (INS placement) prior to the procedure with the patient as sedation may affect their retention of the information given postoperatively. If possible, it is useful to also have a family member or friend present during education for device use.

When only the tined lead is placed, the brown box is set using the Electrode Select switches with one contact set as the negative electrode and one contact set as the positive electrode. The box is then turned on and amplitude is increased until the patient feels the stimulation. If stimulation is not felt comfortably in an appropriate area or the amplitude reaches 10 V, a different combination of positive and negative electrodes should be used. The initial program tried is typically contact 0 set as the negative electrode and contact 3 set as the positive electrode. During the trial, the patient is contacted periodically to assess symptom control and change the program as needed.

If both the tined lead and the INS are implanted, programming is done using the N’Vision Clinician Programmer and the ICon Patient Programmer. An impedance check is performed to assess the lead and the connection of the lead to the INS using the N’Vision Clinician Programmer. As with the brown box, one contact point is set as the negative electrode while a second contact point is set as the positive electrode. Four programs can be set in the ICon Patient Programmer with initial programming set as:

Program 1

Negative 0, Positive 3

Program 2

Negative 1, Positive 3

Program 3

Negative 2, Positive 0

Program 4

Negative 3, Positive 0

The patient is able to adjust the amplitude and switch between the programs as needed using the ICon patient programmer.

Removal of the Tined Lead

If during the trial the target symptoms are not sufficiently controlled, the tined lead should be removed along with the lead extension. This can be performed in the office using local anesthesia or in the operating room using sedation (MAC) and local anesthesia. After prepping the skin, the local anesthetic is administered to the area of the buttock incision overlying the lead connection. The incision and subcutaneous tissue are opened, exposing the connection hub medially. The hub is pulled up into the incision, and the lead extension wire is cut distal to the plastic sleeve. Later, the remaining extension wire is removed from the skin. Traction is then applied to the tined lead until it is removed. If there is significant resistance and the lead begins to elongate, it may fracture during removal. This would rarely if ever occur after only a staged trial. If this is the case, consideration should be given to opening the sacral incision to remove the lead from that location. The lead can usually be removed without opening the sacral incision after the trial period but when the lead has been in place more permanently, the site of the sacral incision usually needs to be opened. Once removed, the wound is irrigated and closed with absorbable suture.

Complications

Potential complications include wound infection, pain related to stimulation or at implantation site, loss of efficacy, or need for magnetic resonance imaging (MRI). If a wound infection develops, all components of the device must be removed. The authors recommend also removing the capsule that forms around the INS. The wound should be irrigated copiously and should usually be left to close by secondary intention by packing the wound. It is important that sufficient time between wound healing and reimplantation occur to try to prevent recurrent infection. The rate of infection noted in a recent trial (InSite) involving implantation in 272 patients was 3.3 % [10]. The infection rate noted in two studies with long-term follow-up as 5 % [925]. In the case of painful stimulation, the first step should be reprogramming to try to get a more comfortable stimulation setting. Pain at the INS site can often be limited by using a bipolar setting. If pain is associated with palpation over the lead site in the pre-sacral area or over the INS, a revision is sometimes necessary. If the lead is too superficial under the skin, it can be uncomfortable and require revision surgery to pass the lead deeper in the subcutaneous tissue. If too small of a pre-sacral incision has been made during lead placement, it can lead to a palpable knuckle of the lead in the pre-sacral skin, or to anterior migration of the lead. This is particularly true in thin patients. Initially making a larger incision, or using an absorbable suture to lay the lead flat against the fascia, can be helpful to prevent this. One group reported pain at the lead site in 5.4 % and pain at the INS site in 15.3 % of patients with long-term follow-up [14]. Another study reported pain with any of the device components in 6.8 % of patients with use of the tined lead [25]. The INS can cause discomfort if placed too superficially, not parallel to the skin, or in too large of a pocket, causing it to move or “flip” within the pocket. It can also cause pain if it sits against a bony prominence. In these instances, the site may need to be revised or the INS may need to be moved to a different location. If the INS is moved to a new incision site, the capsule should be removed from the abandoned implantation site. If it is to be placed deeper or more parallel within the same pocket, the old capsule can serve as a sub-layer, under which the new pocket may be created, and then the capsule can be largely obliterated by using it as a separate closure layer over the newly positioned device.

If the lead is placed ideally along the course of the nerve, allowing all four contact points to have appropriate responses at low stimulation thresholds, it should increase the flexibility in programming by allowing for more potential options. It should also increase the battery life. In general, the average length of battery life for an implanter is a good indication of the quality of lead placements. We frequently have InterStim 2 devices lasting beyond the 5 year mark. When a battery depletes on the short end of its life expectancy, a problem related to lead position is clearly implied. If the patient loses benefit with the therapy, the first step is to evaluate the device in terms of confirming the device is turned on, that the patient is using it properly, estimating remaining battery life, and performing an impedance check. If all of these are normal, the device should be reprogrammed. After reprogramming fails to manage the patient’s symptoms sufficiently, consideration may be given to performing a lead revision, especially if the patient previously had good success with the therapy. During a lead revision, a new lead should be placed with removal of the old lead. With development of the tined lead, the rate of lead revision surgery has decreased as discussed earlier. The decision for simultaneous replacement of the INS depends on the estimated remaining battery life.

There are occasions where an MRI may be warranted in a patient with an implanted device. It has been shown that MRI of the head using an open 1.5 T machine with RF transmit/receive head coil only can be safely obtained in patients with the InterStim device (Medtronic, Minneapolis, MN) [26]. The device should be turned off during the study and the patient should not be sedated, so they can signal any discomfort that may develop during the scan. In patients where an MRI of other areas such as the pelvis or back is required and no other imaging studies are adequate for evaluation of the patient’s condition, the device would need to be removed completely with care taken to remove the entire lead. It is important to avoid implantation initially in patients with a medical condition that will require the routine use of MRI.

Percutaneous Tibial Nerve Stimulation

PTNS is another form of neuromodulation that can be offered to patients with OAB. Neuromodulation is achieved by accessing the posterior tibial nerve above the ankle sending stimulation to the sacral plexus (S2–S4) modulating bladder innervation. Urgent PC is an FDA approved neuromodulation system providing this retrograde stimulation as an office based therapy. The induction therapy consists of 30 min sessions given weekly for 12 weeks and for those that benefit; therapy is maintained with a session every 3–4 weeks thereafter. The Overactive Bladder Innovative Therapy (OrBIT) trial was a randomized control trial performed in patients with urinary frequency comparing PTNS to tolterodine. The patients’ subjective improvement with the initial 12 weeks of therapy was 79.5 % in PTNS group compared to 54.8 % in tolterodine group with objective measures similarly improved in the two groups [27]. A second phase of the trial was performed evaluating the durability of PTNS by extending therapy to 1 year for a group of patients. Sustained improvement was noted in those that initially received benefit from the therapy at 6 and 12 months in 94 % and 96 %, respectively [28].

Procedure

With the patient seated or supine in a comfortable position, the needle electrode insertion site is identified three fingerbreadths superior to the medial malleolus and one fingerbreadth posterior to the tibia. An alcohol pad is used to prep the skin at the insertion site, and the sterile needle electrode (34 Gauge) is placed at a 60° angle to the skin with the tip pointed cephalad. The stop plug is removed and the needle electrode is tapped to pierce the skin and then the guide tube around the needle is removed. The needle electrode is advanced using a twisting motion until approximately 2 cm is inserted. Once the needle electrode has been placed, the grounding pad or surface electrode is attached to medial aspect of the ipsilateral foot and the attached hook is connected to the needle. The lead wire is connected to the stimulator, which is then used to administer 30 min of stimulation. After 30 min, the needle electrode is removed along with the grounding pad/surface electrode. This procedure is repeated for each therapy session. All of the described components are available in the Urgent PC Lead Set (Uroplasty) [29].

Conclusion

OAB affects millions of people worldwide and when conservative therapies have failed to provide adequate management of voiding symptoms, SNM should be considered as the next step in the treatment algorithm. Neuromodulation can be offered in the form of SNS or PTNS. Other indications where SNS is an appropriate treatment option are non-obstructive urinary retention, chronic pelvic pain, fecal incontinence, and childhood dysfunctional elimination syndrome. For SNS, there are two trial methods that may be offered to patients: (1) PNE, (2) Staged Implantation. On multiple long-term follow-up studies, SNS has been shown to be effective and safe. Technological advances such as the tined lead and smaller INS have improved the therapy over time.

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