Intraoperative electromyographic (EMG) monitoring in external anal sphincter using needle electrodes improves sacral neuromodulation (SNM) electrode placement. Due to optimal electrode position lower currents are needed for stimulation which improves SNM outcome and prolongs battery life.

Sacral neuromodulation is a widely used treatment procedure for urinary urgency with or without incontinence, faecal incontinence, and nonobstructive urinary retention. In addition, it has beneficiary effects on refractory pelvic pain and erectile dysfunction. Treatment outcome depends largely on optimal electrode placement within sacral foramen. Currently accepted guidelines for electrode placement rely on visual detection of pelvic floor elevation (bellows response). One study demonstrated that electromyographic muscle detection was more sensitive for pelvic floor contraction, therefore in our department we introduced intraoperative EMG monitoring in for optimal electrode placement in all patients. 

SNM electrode placement is performed in general anaesthesia. Patient is placed in prone position. Gluteal muscles are taped to the side in order to expose anal sphincter to be visible. In addition to visual pelvic floor elevation EMG monitoring is conducted. Monopolar needle electrode is inserted on either side of the sphincter 1 cm from the orifice at 3 an 9 o’clock approximately 1 cm deep. EMG activity is monitored during needle insertion in foramina S3 and S4 with determination of threshold current determination on each site. The electrode is placed in the foramen with lowest threshold and EMG threshold for each of the electrode contacts is recorded. The electrode is repositioned until the threshold currents are appropriate on all four contacts.

At our centre we performed 50 SNM electrode implantations for urinary and/or bowel indications, pelvic pain and in two patients with concomitant erectile dysfunction. The rate of successful test phase was high (92 % for faecal incontinence, 91% for urinary incontinence, 73% for urinary retention in women, and 20% for complete urinary retention in men). The currents needed to reach sensory threshold in patients were in 95% below 1.0 mA, in 10 % as low as 0.2 mA.

With optimal placement of SNM electrode the currents needed to reach sensory threshold are lower comparing to suboptimal placement, therefore the currents needed for SNM efficacy are lower. Acceptable current intensity is 2.0 mA. With EMG monitoring the optimal position can be obtained and the currents needed are significantly lower.

With optimization of electrode placement, the success rate of therapy is higher and the current needed for stimulation is low, which prolongs battery longevity and reduces the possibility of stimulation induced side effects.