Evaluation of external anal sphincter innervation asymmetry in obstetrics

Začesta, Vita and Rezeberga, Dace and Plaudis, Haralds and Drusany-Starič, Kristina and Cescon, Corrado (2016) Evaluation of external anal sphincter innervation asymmetry in obstetrics. In: ISEK 2016 Congress 21 Congress of the International Society of Electrophysiology and Kinesiology, 05.07.2016-08.07.2016, Chicago, USA.

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Recent studies suggest that functional asymmetry of pelvic floor innervation exists in healthy subjects, and it is strongly associated with postpartum incontinence when the trauma occurs on the dominant side of innervation. Episiotomy is the most common cause of perineal trauma during delivery, and the surgical incision is usually performed on the mediolateral right side episiotomy. Surface electromyography (sEMG) in obstetrics is a novel method for detecting the innervation zones (IZ) of external anal sphincter (EAS). The aim of this study is to locate the IZs of EAS by the means of sEMG, and to analyse their distribution, in order to evaluate the effect of episiotomy on the external anal sphincter muscle activity. In this prospective observational type study, 225 pregnant primiparous women (age 28.4 ± 4.1 years) were involved and EMG was performed to detect the distribution of IZs and amplitude of EMG signals of EAS. The EMG measurements were performed two times: during the 2nd trimester of pregnancy and 6 weeks after delivery, in order to recognize any changes in the innervation after delivery. EMG signals were detected by a cylindrical probe with 16 electrodes and acquired with a multichannel amplifier (OT Bioelettronica, Turin, Italy). IZ distribution and signal amplitude were detected before and after delivery. The women were divided in two groups according to the EAS innervation asymmetry: left or right dominantly innervated. The changes of signal amplitude were analysed in subgroups according to the delivery mode (no damage, spontaneous lacerations, caesarean sections and right side episiotomies). Out of the 225 women analysed before delivery 149 women returned after delivery and were used for further analysis: (56) (38%) of them had episiotomy on the right side, (44) (30%) had spontaneous lacerations, (20) (13%) had no damage, and (29) (19%) had Caesarean section. The innervation was observed to be heterogeneous with a tendency of asymmetry predominant on the right side 138 (61%) compared to the 87 women (39%) innervated on the left side. None of the women had any sphincter damage before pregnancy or wound complications after delivery. No significant changes in EMG amplitude were observed in women who had caesarean section or delivery with no damage. While a reduction of amplitude was observed in case of spontaneous lacerations or episiotomy. In particular in case of episiotomy, the women with innervation on the right side had a stronger reduction of EMG amplitude after delivery compared to the women with innervation on the left side, suggesting that choosing the right side of episiotomy could have limited the amplitude changes. Superficial electromyography showed to be a promising method for detecting innervation zones before and after pelvic floor surgery, to avoid iatrogenic damage of pelvic floor innervation.

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