Anatomical feasibility of a peripheral nerve transfer to reestablish the control of the external anal sphincter

Abstract

BackgroundFaulty innervation from pudendal nerve branches is a common cause of anal incontinence, a condition that can severely impact quality of life. Current treatments include medication, rehabilitation, surgical repair of the sphincter and conversion to a definitive stoma. All these options have yielded unsatisfactory results to restore the function of the external anal sphincter, with success rates of approximately 50% (Thinn et al., 2013). Over the last 15 years, an increasing interest in exploring the possibilities of restoring rectum and bladder sphincteric function by means of nerve transfers has produced a number of experimental studies in animal models, indicating promising results (Bao et al., 2018).ObjectiveOur goal was to test the feasibility of dissecting a fascicle of the tibial component of the sciatic nerve to see if it would be long enough to serve as a “donor nerve” for coaptation with the pudendal nerve, in both gluteal and perineal regions.MethodsWe dissected the bilateral gluteal and posterior proximal third of the thigh region in 12 embalmed adult cadavers. We used micro‐surgical techniques to expose the pudendal nerve, the sciatic nerve inferiorly to the piriformis muscle, and the sciatic nerve branches in the long portion of the biceps femoris muscle. We measured the lengths of: (1) the donor nerve (DN) fascicle obtained from the tibial component of the sciatic nerve to the long portion of the biceps femoris muscle; (2) the length required for proximal coaptation (PC): from the cranial‐most point of the donor nerve at the inferior margin of the piriformis muscle to the pudendal nerve at the superior margin of the sacrotuberous ligament; and (3) the length required for distal coaptation (DC): from the cranial most point of the donor nerve at the inferior margin of the piriformis muscle to the pudendal nerve at entrance of the pudendal canal (Alcock's canal). We hypothesized that the ratios DN/PC and DN/DC would be higher than 1, meaning that the donor nerve would be long enough to allow for the development of a novel surgical technique to restore the control of the external anal sphincter in humans.ResultsThe DN length averaged 10.2cm (4.3cm to 14.8cm). The length required for PC averaged 3cm (2.0cm to 4.7cm). The length required for DC averaged 4.8cm (from 3.0 to 7.0cm). The ratio between the DN/PC averaged 3.6, ranging from 1.5 to 6.9, while the ratio between DN/DC averaged 2.3, ranging from 1.5 to 4.4.Conclusionsthe DN was consistently longer than the lengths required for PC and DC, since the ratios DN/PC and DN/DC were significantly greater than 1 across our 24 specimens and in each of our specimens assessed individually (p<0.05). The described peripheral nerve transfer is anatomically feasible. Based on these findings, the next steps are to effectuate and study the surgical transfer in unembalmed cadavers.Support or Funding InformationIn conjunction with the Building Bridges initiativesThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.