Sacral neuromodulation (SNM) is a well-established third-line therapy in refractory overactive bladder (OAB) and among other indications such as non-obstructive urinary retention (NOUR) and fecal incontinence (FI).[1] 

The procedure is typically a two-staged procedure consisting of a tined lead procedure (TLP) and a second phase with implanted pulse generator (IPG) placement. During TLP, the quadripolar lead is evaluated with motor responses on each electrode to confirm that they are sufficiently close to, preferably the sacral nerve S3. Clinicians should strive to achieve motor responses on all four electrodes at stimulus amplitudes of <2 V.[1] This allows stimulation of the lead at various areas of the nerve and indicates optimal anatomical lead position.[2] 

A group studied the predictive value of the optimization of tined lead placement. However, the results of these studies have been contradictory. Some studies have shown that responses to all four electrodes are associated with lower amplitudes for eliciting motor responses, suggesting that the lead is closer to the target nerve.[2] This led to lower revisions but did correlate with more clinical success.[2] Other studies showed no associations between the number of electrodes eliciting motor responses during TLP and short-term outcomes.[2,3] 

This study aimed to correlate peri-operative motor responses during TLP with the clinical success of SNM. We hypothesized that a high number of electrodes eliciting motor responses during TLP correlates with clinical success and a lower likelihood of revision during follow-up. Therefore, we formulated the following research question: “Can the number of electrodes that elicit foot and bellows responses serve as an indicator of the success of TLP and revision rate?”.

This was a single-site retrospective cohort study, encompassing all patients who underwent unilateral staged TLP performed between September 4, 2017, and July 10, 2023. Indications for TLP were wet or dry OAB, NOUR, interstitial cystitis (IC) or FI. Clinical diagnoses were made based on medical history, clinical symptoms, micturition diaries, and urinary dynamic testing. The inclusion criteria was documentation of motor responses for all four electrodes. Patients were excluded in case of neurological disorders, when no primary TLP was performed, or in case of missing data. 

TLPs were carried out in accordance with the International Continence Society's (ICS) best practice statement for the use of SNM.[1] TLPs were performed by a dedicated team consisting of either a urologist or urogynecologist. The preferred nerve root was primarily S3 rather than S4. Motor responses were evaluated by individually stimulating each electrode with three different current intensities: 0.5 mA, 1.0mA, and 2.0 mA. Categorization of foot and bellows responses was as follows: no response (-), good response (+), or very good response (++). After lead placement, nurses evaluated symptoms at the outpatient clinic on a weekly basis during the test phase, typically for 2-4 weeks. Successful TLP was defined as >50% reduction in symptoms.                                                                                    

Data processing
To assess whether the number of electrodes correlated with clinical success or the need for revision, the following scoring system was used: each electrode that produced a good (+) or very good (++) motor response, 1 point was given for a maximum possible score of 4. In case of an absent motor response (-) on a single electrode, 0 points were given. A cumulative score of 8 was achieved when the foot and bellows responses were combined. No difference in score was made between a good (+) or very good response (++).

Baseline characteristics
A total of 149 patients were eligible for the study. We evaluated the records of 87 patients who fulfilled the inclusion criteria. The cohort comprised 73 (84%) female patients with a mean age of 52.4 (± 1.7) years (Table 1). Overall, 40 (46%) patients had SNM indications for OAB (Table 2). 

Number of electrodes active during tined lead procedure 
Scores of foot and bellows responses were analyzed for each electrode and cumulatively (Table 2).These variables were analyzed and compared between responders and non-responders for each outcome: clinical success or requirement of revision. There were no significant differences between the groups for each outcome. This applied for foot and bellows response separately as well as cumulatively. 

Correlation between motor response and TLP success and revision rates
Logistic regression analyses were conducted to examine the association between the number of electrodes and TLP outcomes as well as the association between revision during follow-up. The results showed no significant association with odds ratio. This applied to foot and bellows responses and both outcomes; TLP succes and the chance of revision, for each electrode separately or cumulatively.

This study showed no correlation between the number of electrodes stimulated during tined lead procedure and clinical outcome. Similarly, this also applies to revision requirements. These analyses were applied to both individual electrodes and cumulative electrodes for each foot or bellow response. This implies that effective test stimulation probably requires only a single well-positioned electrode to provide a successful test phase.

Our study revealed that the number of electrodes eliciting motor responses during TLP did not influence clinical success or revision rates. However, it is important to consider all electrodes to optimize the program options and strive for durable SNM therapy. However, during test stimulation, only a single well-positioned electrode is necessary to achieve clinical success.

Goldman HB, Lloyd JC, Noblett KL, Carey MP, Castaño Botero JC, Gajewski JB, Lehur PA, Hassouna MM, Matzel KE, Paquette IM, de Wachter S, Ehlert MJ, Chartier-Kastler E, Siegel SW. International Continence Society best practice statement for use of sacral neuromodulation. Neurourol Urodyn. 2018 Jun;37(5):1823-1848. doi: 10.1002/nau.23515. Epub 2018 Apr 11. PMID: 29641846.
Pizarro-Berdichevsky J, Gill BC, Clifton M, Okafor HT, Faris AE, Vasavada SP, et al. Motor Response Matters: Optimizing Lead Placement Improves Sacral Neuromodulation Outcomes. J Urol. 2018 Apr;199(4):1032-1036. doi: 10.1016/j.juro.2017.11.066. Epub 2017 Nov 14. PMID: 29154850.
Gill B, Thomas S, Barden L, Jelovsek J, Meyer I, Chermansky C. Intraoperative Predictors of Sacral Neuromodulation Implantation and Treatment Response: Results From the ROSETTA Trial. J Urol. 2023 Aug;210(2):331-340. doi: 10.1097/JU.0000000000003498. Epub 2023 Apr 26. PMID: 37126070;