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European Urology

Volume 54, issue 6, pages 1209-1454, December 2008

Surgery in Motion

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Latest Technologic and Surgical Developments in Using InterStim™ Therapy for Sacral Neuromodulation: Impact on Treatment Success and Safety

Michele Spinelli a lowast , Karl-Dietrich Sievert b.

Accepted 21 January 2008, Published online 8 February 2008, pages 1287 - 1296

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Abstract

Objectives

This article accompanies a “surgery in motion” DVD on sacral neuromodulation (SNM) with InterStim™ Therapy, which visualizes the implantation of the InterStim II system. The article describes the technical and surgical developments of SNM and their impact on treatment success, safety, and patient's quality of life (QoL).

Methods

Relevant literature on SNM with regard to technical changes and related clinical outcomes has been reviewed.

Results

Since its introduction in the early 1990s, SNM has proven useful in the treatment of several types of chronic urinary (and bowel) dysfunction. Recent technical improvements in devices and, in particular, the introduction of the tined lead 5 yr ago made SNM progress from an elaborate, open-surgery, general anesthesia, one-stage implant procedure to a minimally invasive, local anesthesia, percutaneous technique in two stages. The permanent tined lead implant enables a longer patient testing period (minimum of 14 d recommended) and less lead migration. This has considerably reduced technical failures and improved the success rate of the test phase; the response rate was almost doubled to approximately 80%. These improvements also affected tolerability, resulting in increased QoL for the patient. The use of the recently introduced smaller implantable neurostimulator InterStim II seems to further improve patient comfort and makes the implant procedure for the physician easier and shorter. However, this must be further addressed in clinical studies.

Conclusions

SNM with InterStim Therapy using the tined lead offers an efficient treatment modality for patients in whom conservative treatment has failed.

Take Home Message

The introduction of the tined lead as permanent lead for a two-staged implant procedure and other technical and surgical improvements make sacral neuromodulation with InterStim™ Therapy a useful treatment modality in the urologic field.

Keywords: Efficacy, Electrode, Quality of life, Sacral neuromodulation, Safety, Therapy, Tined lead, Urinary dysfunction.

Article Outline

1. Introduction

Chronic voiding dysfunctions can considerably impair the patient's quality of life (QoL). These include overactive bladder (OAB), also referred to as the urgency-frequency syndrome, with or without urge urinary incontinence (UUI), and nonobstructive urinary retention (UR) [1], and [2]. Diet modifications, behavioral therapy (ie, pelvic floor training, biofeedback), and medication belong to the standard conservative therapeutic options. If no symptomatic improvement is reached and/or the patient cannot tolerate the side effects of antimuscarinics, invasive surgical procedures, such as sphincteroplasty, augmentation cystoplasty, urinary diversion, among others, can be performed. However, potential disadvantages of these surgical therapies include limited efficacy, potentially severe complications, and irreversibility. These considerations underline the need for alternative therapies, such as electrostimulation, which has been used in urology for a long time. Direct stimulation and subsequent modulation of the sacral nerves has been proven effective and is today an established treatment option for patients refractory to or intolerant of conservative treatments.

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2. Methods

This paper accompanies a “surgery in motion” DVD on sacral neuromodulation (SNM) with InterStim™ Therapy, which demonstrates the implantation of the InterStim II system. A literature search was performed in the PubMed database and relevant publications on the SNM technique, its technical and surgical evolution, and the clinical outcomes (efficacy and safety) related to these developments were selected.

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3. Results

3.1. Sacral neuromodulation

SNM uses mild electrical pulses to activate or inhibit neural reflexes by continuously stimulating the sacral nerves that innervate the pelvic floor and lower urinary tract; it is also referred to as the pacemaker for the bladder. SNM was introduced in 1979 by Tanagho and Schmidt at the University of California in San Francisco [3]. From this first experimental use of SNM by surgically implanting an electrode around selected sacral nerves in dogs, InterStim™ Therapy was developed by Medtronic (Minneapolis, MN, USA) for use in humans. It first received CE marking in Europe in 1994 and obtained Food and Drug Administration (FDA) approval for the first urologic indication in October 1997 [4]. Since then, InterStim Therapy has continuously evolved in terms of knowledge of its mode of action as well as in technical and surgical aspects. Although its mode of action is still not completely known, recent research indicates that it involves not just electrostimulation of sacral nerves but also neuromodulation due to somatosensory bladder afferents projecting into the pontine micturition center in the brain stem [5]. A retrospective study in 107 patients with OAB and 42 with UR who received SNM implants and were followed for a mean of 64.2 mo revealed that over the period 1999–2003 reoperation and adverse event rates dropped strikingly. The mean reoperation rate was reduced from 1.56 before to 0.49 after 1995 (p < 0.0001). These results have been attributed to the learning curve of physicians and technical and surgical improvements in the application of SNM [6].

3.2. One-stage versus two-stage implant of InterStim Therapy

The InterStim Therapy procedure is done in two phases. The first phase or the test phase allows the physician to test the patient's initial response with an external neurostimulator device before proceeding to the second phase, that is, the permanent implantation of the neurostimulator device. To assess viability of SNM and to allow selection of responsive patients, testing consists of an acute stimulation period followed by a subchronic stimulation period with home evaluation.

3.2.1. One-stage implant

Initially, the percutaneous nerve evaluation (PNE) technique was used for the testing phase. With this technique, an insulated thin wire is placed into the third sacral nerve (S3) foramen in the vicinity of S3 with the patient under local anesthesia. This temporary unipolar lead is connected to an external neurostimulator and taped to the skin surface. Patients with at least 50% symptom improvement from baseline (the definition of response or success reported in studies on SNM) proceed to removal of the temporary lead followed by implantation of a quadripolar permanent lead and implantable neurostimulator (INS) placement. This is referred to as the one-stage implant because the permanent quadripolar lead and the INS are implanted at the same time. Remarkably, some patients do not have a successful test but still respond well to permanent SNM therapy with sustained clinical benefit [7]. An explanation for this false-negative result with the one-stage implant procedure may be that the temporary electrode is prone to migration during the subchronic test phase. The unipolar structure of the temporary lead compared to the quadripolar permanent lead might even enhance the effect of migration on success rate [8]. In addition, the duration of this test is limited to a maximum of 2 wk because longer implantation of the temporary lead may increase the probability of bacterial contamination of the test stimulation lead [9]. Significant restrictions, such as no showering, also dictate short-term testing. This short-term testing period as well as the lead migration probably explain the relatively low success rate of PNE, estimated at around 50% [10], [11], and [12]. Furthermore, up to 33% of the patients who have a beneficial test stimulation with a temporary lead do not continue to have a successful outcome after the INS is implanted, or in other words, are false-positive responders [13]. Exchange of leads during the one-stage implant procedure may contribute to therapy failure during follow-up. Therefore, better patient selection to reduce false-negative and false-positive responders was considered important for further improvement of SNM outcome. It was believed that this could be achieved by finding predictive factors and/or by improving the classical testing technique [8]. An attempt to improve the response rate has recently been made by modifying the PNE technique [14]; however, this should be confirmed by further studies and/or more widespread clinical experience.

3.2.2. Two-stage implant

To minimize technical-related failures and increase test efficacy, several successive modifications have been made in the technology, which finally led to the development of currently practiced InterStim Therapy in our institutions. The most significant change was the shift from PNE (one-stage implant) to a two-stage procedure. The first stage refers to the implanting of a permanent lead for testing the response to SNM (Fig. 1 A) [7]. In the second stage, patients who are responsive after testing have the INS implanted (Fig. 1 B). The latter consists only of a minor surgical intervention.

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Fig. 1 Two-stage implant of InterStim Therapy. (A) Implant of the permanent lead during the testing phase for selecting responsive patients and (B) implant of the implantable neurostimulator (INS) in responsive patients.

Immediate implantation of a permanent lead aims to avoid lead migration and allows prolonged patient testing/screening [8], and [12]. The percentage of patients proceeding to permanent implant of the INS is almost doubled when using the permanent lead as compared to the temporary PNE test approach (shown for refractory interstitial cystitis) [11] (Fig. 2). Sensory response assessment at the time of implantation reduced the reoperation rate from 43% to 0% [11]. The two-stage implant procedure has also a better long-term outcome than the procedure with traditional PNE testing. A prospective, randomized study showed that the two-stage implant technique of SNM has after the INS implant a higher success rate compared to the one-stage method, despite prior positive PNE, both in the short term and in the long term [13]. In this regard, it is important to evaluate SNM with the permanent lead for a minimum of 14 d (14 d for unilateral and 28 d for bilateral testing). An increase in responders (≥50% improvement in symptoms) from 50% to 80% has been described when this time period for testing is respected, compared to an evaluation period of 4–7 d [8].

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Fig. 2 Use of a permanent (tined) lead (two-stage implant) almost doubles the implantable neurostimulator implant rate as compared to usage of percutaneous nerve evaluation (PNE)/temporary lead (one-stage implant) [10], and [11].

3.3. Tined lead
3.3.1. Development of the tined lead

At first, the permanent lead placement was secured by fascial fixation with the patient under general anesthesia. A refined fixation method with twist locks or silicone anchors allowed a smaller incision under conscious sedation and, as such, a less invasive approach [15]. To further improve the technical features of the lead, a self-anchoring tined lead was designed, which received CE marking and FDA approval in 2002. The tined lead comprises four sets of silicone tines proximal to the electrodes as an integral part of the lead body, with each tine element consisting of four flexible, pliant tines (Fig. 3). The system engages subcutaneous tissue, particularly muscle tissue, to decrease axial movement of the lead and consequent dislodgment of the stimulating electrodes.

The particularity of the tined lead is that the two-stage implantation can be conducted in a fully percutaneous and simplified way [16]. Furthermore, this technique does not preclude other treatment options and can, in contrast to surgical interventions, be easily reversed. It offers the advantage of a truly minimally invasive approach for SNM, performed under local anesthesia in an outpatient setting. As such, in addition to fluoroscopy of identification marks on the lead and motor responses (bellows contractions of the anus), the patient's conscious sensory responses (vaginal, perineal, or rectal) are accessible. These sensory responses may be helpful to allow a more accurate placement of the permanent tined lead, although it has been reported that the motor responses better predict first-stage test success than the sensory responses [17].

3.3.2. Permanent (tined) lead versus PNE testing

A positive outcome during screening with the tined lead was reported for 77–90% of the tested patients [10], [16], and [18]. SNM with the tined lead resulted in permanent implant of the INS in significantly more patients with UUI than with PNE (88% vs. 46%; p = 0.02; Fig. 2). However, responders to both test stimulation techniques showed similar improvements in 24-h pad weight, daily pad usage, daily incontinence episodes, and visual pain analogue scores [10]. Depending on the country, PNE with the temporary lead (one-stage implant) and/or the two-stage implant with the permanent tined lead are currently used in clinical practice.

3.4. InterStim Therapy two-stage tined lead placement technique

The minimally invasive operative procedure to test and apply InterStim Therapy with the tined lead is performed with an insertion kit consisting of a foramen needle, a directional guide wire, a dilator with a concentric plastic sheath, and the tined lead [16] (Fig. 4). The patient is placed in the prone position with a 45° flexion of the hips and knee joints. By using local anesthesia and intravenous conscious sedation, the foramen needle is inserted in the S3 foramina (Fig. 5). After ensuring correct sensory and motor responses, the inner stylet of the needle is removed and replaced with the directional guide. The foramen needle is replaced by the dilator covered by the introducer sheath and thereafter the directional guide and dilator are removed, leaving the introducer sheath in position. Finally, the tined lead is inserted until the proximal electrode enters the foramen. To verify the lead's position in addition to fluoroscopy, an electrical stimulus is applied to evoke motor and sensory responses. With the lead held in place, the introducer sheath is retracted. The tined lead is tunneled subcutaneously to the future implant pocket of the INS. Through a small incision at that ipsilateral place, an extension cable is introduced for connecting the tined lead subcutaneously to a pulse generator. The latter is situated at the contralateral side and is external during the first stage (Fig. 1 A). This transposition with long tunneling is chosen to prevent infection. In the second stage, the INS is implanted into the upper gluteal region in a sub-adipose pocket (Fig. 1 B). At the end of each stage of the procedure and whenever there is a decrease in symptomatic response, sacral x-rays are recommended [19].

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Fig. 4 Minimally invasive placement of the tined lead electrode by means of a sacral percutaneous implant kit [18].

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Fig. 5 Subcutaneous implant of the permanent tined lead in the third sacral nerve (S3) foramen during the two-stage procedure.

Buttock placement of the INS has become an alternative to subcutaneous implant in the lower part of the anterior abdominal wall because of the lower incidence of adverse events (approximately 2-fold), shorter operation time, and avoidance of patient repositioning during the operation [20].

3.5. Clinical results of InterStim Therapy when using the tined lead
3.5.1. Efficacy of the tined lead
3.5.1.1. Success rate of test stimulation and efficacy following implant

Unless stated otherwise, an improvement of ≥50% from baseline in outcome variables (defined depending on the indication) was considered successful.

In a prospective, European, multicenter study in 94 patients with different types of voiding dysfunction, screening with the tined lead was performed for on average 30 d, which was successful in 72 patients (76.6%) [18]. At 6 wk, 70 patients (74%) responded and received the INS. After 6 mo, follow-up data were available for 20 patients with UUI and 21 patients with UR. Patients with UUI had a significant reduction in the mean number of daily voids (p < 0.001), incontinent episodes (p < 0.005), and replaced pads (p = 0.0069; Fig. 6). Patients with UR experienced improvements in the mean number of self-catheterizations (from 4.0 to 1.2; p < 0.001), voids per day (from 3.2 to 5.6; p < 0.001), and catheterization volume (from 328.4 to 99.3 ml; p < 0.001) [18].

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Fig. 6 InterStim Therapy with the tined lead in patients with urinary urge incontinence leads to a significant improvement in urinary variables (n = 20) [18]. SNM = sacral neuromodulation.

A small retrospective but longer-term study with the tined lead involved 25 women with refractory UUI with a mean follow-up of 7.2 mo [21]. Twenty patients (80%) had ≥50% improvement in clinical symptoms; responders showed a significant reduction in daily pad usage, decreasing by 74% from 4.2 to 1.1 (p < 0.001) and six patients (24%) became fully continent (requiring no pads) [21]. Similar success rates were achieved in another retrospective study on patients with OAB or UR, of whom 31 of 39 patients (79%) responded; 90% of these 31 patients had >50% improvement in at least one of the relevant voiding diary variables after a mean follow-up of 15.5 mo [22]. In the 21 patients with UUI or urgency-frequency, the mean number of voids and incontinence episodes per day decreased although the difference was not statistically significant (Fig. 7). The mean voided volume increased significantly with 44% (from 160.2 to 231.1 ml; p = 0.001).

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Fig. 7 Long-term InterStim Therapy with the tined lead in patients with refractory overactive bladder (n = 21, urinary urge incontinence and urgency-frequency) improves the voiding frequency and the number of daily leakages [22]. SNM = sacral neuromodulation.

Application of the general SNM technique on patients with UUI resulted in cure rates of 47% after 6 mo that sustained to at least 18 mo [4]. After 3 yr, a cure rate of 32% has been reported [23].

3.5.1.2. Predictive factors

Some studies were undertaken to evaluate factors associated with test and therapy response to SNM to help identify the most appropriate therapy candidates. A prospective analysis on 55 patients refractory UUI, who had a positive SNM response after a mean of 29 mo, associated cure rate (defined as no leakage episodes after implant) with age; patients younger than 55 yr had a better cure rate (65% vs. 37%; p < 0.05) [24]. Also the number of chronic conditions and the neurologic state affected outcome [24]. A retrospective small cohort study in 34 women with refractory UUI after a stress incontinence surgery confirmed that age predicts outcome of SNM testing (the percentage of patients older than 55 yr was 59.1% in responders vs. 100% in non-responders; p = 0.01). Other factors predictive of a positive response were evidence of pelvic muscle activity (the percentage of patients with pelvic floor muscle ≤2 was 15.4% in older responders vs. 62.4% in older non-responders; p = 0.03) and test stimulation performed within 4 yr (the percentage of patients having surgery >4 yr ago was 13.6% in responders vs. 62.5% in non-responders; p = 0.01) [25]. In contrast, others found, after a mean follow-up of 7.2 mo, no significant differences in response to SNM based on age, symptom duration, or urodynamic variables [21] and no correlation between the presence or absence of detrusor overactivity and response to test stimulation [26]. In a retrospective analysis of 29 patients with nonobstructive UR, neither the patients’ gender nor age influenced the outcome of SNM test stimulation [27]. However, those who were able to void >50 ml and/or with longer duration of retention were significantly more likely to experience a ≥50% improvement in catheterization frequency and/or voided volume.

3.5.2. QoL since the tined lead use

Because voiding dysfunctions in general may have a serious impact on a person's daily activities and social life, the effect of treatment on disease-specific QoL also reflects its efficacy. Concerning the impact of SNM with the tined lead, a single-center study in 49 patients with refractory UUI evaluated their satisfaction at least 1 yr after implantation (mean 27.2 mo) [28]. Satisfaction was assessed by a simple questionnaire and disease-specific health-related QoL by means of the Incontinence Impact Questionnaire (IIQ) short form. Of all mail respondents, 84% were satisfied and 80% would choose the same treatment if they had to do it all over again. Compared with dissatisfied patients, satisfied patients demonstrated a significant improvement in 24-h pad weight during test stimulation (mean 84.5% vs. 60.6%; p = 0.002), in IIQ score (mean score 52.7 vs. 10.0; p = 0.0003), and in daily pad usage (mean 4.1 vs. 1.1; p = 0.005) [28].

3.5.3. Safety since the tined lead use

Despite obtaining clinical responses after INS implant, a decline in efficacy or the occurrence of adverse events may require explantation of the system. However, a surgical intervention is not necessary in all cases. Potential lead migration can be easily resolved without significant morbidity in the majority of patients by reprogramming, reinforcing the lead, or inserting a new lead contralaterally [19]. Also for adverse stimulation, it may be sufficient to change the stimulation factors (eg, electrode configuration, pulse width, amplitude, mode, or polarity).

Despite the tines, lead migration after tined lead placement can still occur as observed in a case study of a thin patient [29] and in 2.1% of 235 patients [19]. To illustrate that nonoperative revision may be sufficient, Hijaz et al retrospectively analyzed 214 patients with various bladder dysfunctions managed in their institution of whom 161 (75%) proceeded to second-stage implant. After a mean of 16 mo of follow-up, the explantation rate was 10.5%; this was mainly due to infections (5.0%) and lack of sustained efficacy (5.6%) [30]. In 16.1% of patients, lowered response (10.6%) and complications, such as INS site discomfort (2.5%), lead migration (0.6%), and infection (2.5%), could be successfully managed by revision [30]. The authors conclude that lead migration and INS site discomfort were relatively uncommon in their study, which may be attributed to the introduction of the tined lead and gluteal placement of the INS, respectively [30]. This suggestion is also illustrated by a recently published single-center study that described its 11-yr experience with SNM for the treatment of refractory voiding dysfunction [31]. In a population of 104 patients, 155 leads were placed over time, including 52.9% non-tined leads (preceded by a PNE) and 47.1% tined leads (performed as a two-stage implant procedure). Approximately three times as many non-tined leads experienced a loss or lack of efficacy after an initial period of success as compared to tined leads. Tined leads also had a lower rate of reportable events (28% vs. 73%, respectively) [31]. However, more, longer-term studies are needed to confirm that the tined lead is, indeed, associated with a lower risk of lead migration and adverse events.

3.6. Latest technologic improvements: development of InterStim II

Recently, several technical aspects of SNM with InterStim Therapy led to the development of the InterStim II system, which received regulatory approval in Europe and the United States in 2006. The new InterStim II INS eliminates the need for extension cables and is almost 50% lighter and smaller in volume compared to the initial INS model (Fig. 8). To date, only a post-market Web-based survey among 11 European experts in urology, gynecology, and gastroenterology evaluated their initial experience with the new InterStim II Therapy in 55 patients [32]. The smaller size of the new InterStim II INS allowed for a smaller incision and smaller pocket (3.5 cm smaller) to be made. This seemed to lead to a further minimally invasive surgical technique resulting in less patient discomfort with higher patient acceptance (Fig. 9), especially in skinny patients. The lack of an extension cable allowed an easier and shorter implant (on average 14 min less) with a reduced operation time (on average 10 min less; Fig. 9). Furthermore, the new small iCon patient programmer, offering the patient the possibility to choose from up to four preset programs, provided better control of stimulation by the patient.

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Fig. 8 The new implantable neurostimulator II is smaller and eliminates the need for an extension cable for connection with the tined lead.

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Fig. 9 The new implantable neurostimulator II features are positively evaluated in a Web-based survey among European physicians [32].

3.7. InterStim Therapy in comparison with other minimally invasive treatments

Intradetrusor injection of botulinum toxin A, a reversible nerve toxin, is increasingly used as a minimally invasive treatment for patients with OAB although it is not approved by the FDA or European Medicines Agency (EMEA) for urologic indications. Despite limited clinical experience, short-term efficacy data from clinical trials are promising because 3 mo of treatment with 100–200 U botulinum toxin A improves OAB symptoms by approximately 50% and incontinence episodes by 70% (as compared to >70% with SNM [12], [21], and [33]) [34], and [35]. However, the effect lasts for only 5–6 mo, after which repeat injections are necessary [34], [36], [37], and [38]. Cure rates of 50% have been reported in patients with idiopathic OAB at 24 wk [35]. The most commonly reported adverse events with botulinum toxin A are urinary tract infection and increased postvoid residual (15–33%) with the potential risk to end in acute urinary retention (AUR: 7–31%). In addition, de novo clean intermittent (self)-catheterization (4–38%) may be required because of high postvoid residual or AUR [34], and [35]. This is an undesirable adverse event for patients with idiopathic OAB who were catheter-free before treatment started. Long-term efficacy and safety data on botulinum toxin application are lacking. In contrast to botulinum toxin A, SNM with InterStim Therapy is approved by the FDA and has received CE marking for urologic indications, is reversible at any time, and can treat concomitant pelvic floor morbidities such as UR, pain, chronic fecal incontinence or constipation.

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4. Discussion

Over recent decades, SNM has offered therapeutic benefit to patients with chronic lower urinary tract dysfunction, who have not been treated sufficiently by other approaches. InterStim Therapy has evolved from an elaborate technique to a minimally invasive, percutaneous, and reversible treatment that can be performed under local anesthesia in an outpatient setting [16], and [18]. This has been established by several technical and surgical improvements, such as the development of the tined lead [16], and [18] and the new InterStim II INS. In the first phase of the two-stage implant procedure, the self-anchoring tined lead is percutaneously and permanently implanted and used to select patients for definitive INS implant. This test method seems more reliable and effective than the classic PNE because the success rate (defined as ≥50% symptom improvement from baseline) has almost been doubled from approximately 50% to 80%. Several studies with the tined lead have shown a favorable short- and long-term efficacy and impact on QoL for patients with different urologic conditions. The reduced size of the InterStim II INS and the lack of an extension cable seem to make the implant easier and the operation shorter and to provide more comfort for the patient but should be confirmed in prospective clinical studies.

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5. Conclusions

SNM with InterStim Therapy offers a useful treatment modality in the urologic field for patients in whom conservative treatment has failed.

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Financial disclosures: K.-D. Sievert is supported by research grant of Medtronic Inc. Azienda Ospedale Niguarda Cà Granda has an agreement with Medtronic Italia SpA for providing training and education on InterStim™ Therapy.

Acknowledgment statement: The authors are grateful to Ismar Healthcare NV for their assistance in editing of the manuscript. The authors are appreciative of the substantial work by Bastian Amend (UKT) who is a co-first author in the Surgery in Motion video production (Title: Implantation of two Interstim II neurostimulators with abdominal or buttock positioning).

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Footnotes

a Unità Spinale Unipolare, Azienda Ospedale Niguarda Cà Granda, Milan, Italy

b Urology Department, University of Tübingen, Tübingen, Germany

lowast Corresponding author. Unità Spinale Unipolare, Azienda Ospedale Niguarda Cà Granda, P.zza Ospedale Maggiore 3, 20162 Milan, Italy. Tel. +39 02 97 69 3343; Fax: +39 02 97 96 3342.

Article information

PII: S0302-2838(08)00130-9
DOI: 10.1016/j.eururo.2008.01.076
© 2008 European Association of Urology. Published by Elsevier B.V.

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