Length tension function of puborectalis muscle: implications for the treatment of fecal incontinence and pelvic floor disorders.

BACKGROUND/AIMS: External anal sphincter (EAS) and puborectalis muscle (PRM) play important role in anal continence function. Based on length-tension measurement, we recently reported that the human EAS muscle operates at short sarcomere length under phys-iological conditions. Goal of our study was to determine if PRM also operates at the short sarcomere length. METHODS: Length-tension relationship of the PRM muscle was studied in vivo in 10 healthy nullipara women. Length was altered by vagi-nal distension using custom-designed probes of 5, 10, 15, 20, 25 and 30 mm diameters as well as by distending a poly-ethylene bag with different volumes of water. Probes were equipped with a reverse perfuse sleeve sensor to measure vaginal pressure (surrogate of PRM tension). PRM electromyogram (EMG) was recorded using wire electrodes. Three-dimensional ultra-sound images were obtained to determine effect of vaginal distension on PRM length. RESULTS: Ultrasound images demonstrate distension volume dependent increase in PRM length. Rest and squeeze pressures of vaginal bag increased with the increase in bag volume. Similarly, the change in vaginal pressure, which represents the PRM contraction increased with the increase in the probe size. Increase in probe size was not associated with an increase in EMG activity (a marker of neural drive) of the PRM. CONCLUSIONS: Probe size dependent increase in PRM contraction pressure, in the presence of constant EMG (neural input) proves that the hu-man PRM operates at short sarcomere length. Surgically adjusting the PRM length may represent a novel strategy to improve treat anal continence and possibly other pelvic floor disorders.(J Neurogastroenterol Motil 2014;20:539-546).

Purse-string morphology of external anal sphincter revealed by novel imaging techniques.

The external anal sphincter (EAS) may be injured in 25-35% of women during the first and subsequent vaginal childbirths and is likely the most common cause of anal incontinence. Since its first description almost 300 years ago, the EAS was believed to be a circular or a "donut-shaped" structure. Using three-dimensional transperineal ultrasound imaging, MRI, diffusion tensor imaging, and muscle fiber tracking, we delineated various components of the EAS and their muscle fiber directions. These novel imaging techniques suggest "purse-string" morphology, with "EAS muscles" crossing contralaterally in the perineal body to the contralateral transverse perineal (TP) and bulbospongiosus (BS) muscles, thus attaching the EAS to the pubic rami. Spin-tag MRI demonstrated purse-string action of the EAS muscle. Electromyography of TP/BS and EAS muscles revealed their simultaneous contraction and relaxation. Lidocaine injection into the TP/BS muscle significantly reduced anal canal pressure. These studies support purse-string morphology of the EAS to constrict/close the anal canal opening. Our findings have implications for the effect of episiotomy on anal closure function and the currently used surgical technique (overlapping sphincteroplasty) for EAS reconstructive surgery to treat anal incontinence.

Evidence for the innervation of pelvic floor muscles by the pudendal nerve.

OBJECTIVE: To evaluate whether the pudendal nerve innervates the levator ani muscles by assessing the effect of pudendal nerve blockade on pelvic floor muscle function. METHODS: Eleven nulliparous women without symptoms of anal or urinary incontinence were studied before and after pudendal nerve blockade with vaginal manometry, electromyography of the external anal sphincter and puborectalis muscle, and 3-dimensional transperineal ultrasound imaging of the urogenital hiatus during rest and squeeze. RESULTS: After pudendal nerve blockade, mean vaginal resting pressures decreased from 19 +/- 10 mm Hg to 15 +/- 10 mm Hg (P < .05), and mean vaginal squeeze pressures decreased from 61 +/- 29 mm Hg to 37 +/- 24 mm Hg (P < .05). After pudendal nerve blockade, the anterior-posterior length of the urogenital hiatus increased from 51 +/- 4 mm to 55 +/- 5 mm at rest (P < .05) and increased from 47 +/- 3 mm to 52 +/- 5 mm during squeeze (P < .05). Resting and squeeze electromyography amplitude of the external anal sphincter and puborectalis muscle was markedly reduced by pudendal nerve blockade. CONCLUSION: Pudendal nerve blockade decreases vaginal pressures, increases length of urogenital hiatus, and decreases electromyography activity of the puborectalis muscle, all of which suggest that the pudendal nerve does innervate the levator ani muscle.