The external anal sphincter and the role of surface electromyography

Abstract

Assessment of the neuronal control of the external anal sphincter (EAS) has long been restricted to investigating patients with defecation disorders by invasive tools such as needle electromyography (EMG), while less invasive techniques have been regarded as non-suitable for diagnostic purposes. Multichannel surface EMG by means of electrode arrays applied to anal sphincter muscle records and identifies individual motor unit action potentials, their place of origin along the circumference, their repetitive firing frequency, and their progression along the muscle fibres at different levels within the anal canal. These data shed doubts on conventional knowledge about the anatomy of the EAS muscle, and confirms new concepts of anatomical differences between gender. This may eventually be transferred to a new understanding of the role of symmetry and asymmetry of pelvic floor innervation and its role in the pathogenesis of fecal incontinence.

Repeatability of innervation zone identification in the external anal sphincter muscle

“…Several motor unit (MU) action potentials (MUAP) traveling across different channels can be identified 13 and the position of the IZ of the identified MUAPs along the circumference can be estimated. [13][14][15] Great attention has recently been devoted to the assessment of the distribution of IZ of EAS (see Digestion, volume 69, 2004 Our method is completely different from other techniques, which do not measure electrophysiological variables, such as the location of the IZ and its asymmetry. It is expected that this totally new information extracted from multi-channel surface EMG can support the development of a technique of clinical relevance.…”

Circumferential urinary sphincter surface electromyography: A novel diagnostic method for intrinsic sphincter deficiency

“…2 mm long, 1 mm diameter) each in a single differential configuration. The use of a multichannel approach allows concomitantly detection of bipolar EMG signals from a number of locations across the muscle . EMG signals were detected up to 1 cm depth.…”

Automatic localisation of innervation zones: A simulation study of the external anal sphincter

“…The conductivity of the mucosa is 1 S/m and the conductivity of the EAS and IAS muscles c d The thickness of the mucosa layer is 1 or 3 mm, in two sets of simulations. The thickness of the IAS is 1 mm (Enck et al, 2005).…”

“…With this technique, it is possible to identify the individual motor unit action potentials (MUAP) in the EMG signal, estimate the position of their IZ along the circumference, and follow the propagation of the action potentials along the muscle fibres (Enck et al, 2004b). Some preliminary studies based on multi-channel detection of surface EMG indicated anatomical differences between genders (Enck et al, 2004b(Enck et al, , 2005, and assessed the correlation between childbirth-related sphincter injuries and faecal incontinence symptoms (Wietek et al, 2007).…”