Obstetric Trauma Third-and fourth-degree lacerations at delivery are associated with an increased risk of fecal incontinence (odds ratio [OR] 3.09) (55). Whereas the incidence of clinically documented third-and fourth-degree anal sphincter tears is between 0.5% and 5.9% (51,53,57), occult third-and fourth-degree defects are present in 28% to 35% of primiparous women and 44% of multiparous women, and approximately one-third of these patients have symptoms of anal incontinence. Patients with occult anal sphincter tears are 8.8 times more likely to have fecal incontinence (53,58). Forceps-assisted vaginal delivery significantly increases this risk, but the data on vacuum-assisted delivery are less conclusive (52,59,60). Elective cesarean delivery, in contrast with emergency cesarean delivery, was believed to prevent anal incontinence, but recent studies argue against any protective effect with cesarean delivery, irrespective of timing (46,51,53,59,61,62). A recent Cochrane review concludes that there is insufficient evidence to support primary elective cesarean delivery for the purpose of preserving fecal continence (63). Midline episiotomy is strongly linked to sphincter damage and fecal incontinence (52,64). One study of a large population found conﬂicting results, with an overall protective effect seen with episiotomy (OR 0.89). The likelihood of fourth-degree laceration was increased (OR 1.12) and of third-degree laceration was decreased (OR 0.81) (51). A Cochrane review supports the restrictive use of both midline and mediolateral episiotomy due to less posterior perineal trauma, less suturing, and fewer healing complications. There were no differences in severe trauma, pain, dyspareunia, or urinary incontinence, but there was an increase in anterior perineal trauma with restrictive use (65). An important finding in another study was that one-half of patients who underwent immediate repair of a third-degree laceration had symptoms of anal incontinence, and 85% had persistent sphincter defects on endoanal ultrasonography (66).
Surgical Trauma Iatrogenic injury follows obstetric trauma as the second most common cause of direct sphincter damage. Surgical procedures that have been associated with fecal incontinence include anal fistula repair, anal sphincterotomy, hemorrhoidectomy, and anal dilation. Fistulotomy is the most common procedure that results in fecal incontinence. Rectovaginal or anovaginal fistulas can develop after obstetric injury, operative complications during pelvic surgery, and inﬂammatory bowel disease exacerbations. Fistulas cause fecal incontinence, and the degree of postoperative dysfunction depends on the location of the fistula and the amount of sphincter that is disrupted during the surgical repair. It also depends on the preoperative level of sphincter function and pudendal nerve function. Anal sphincterotomy to treat painful anal fissures can lead to incontinence by disruption of rectal sensory innervation and anal cushions and transection of the anal sphincter (67,68). Hemorrhoidectomy often results in minor soiling as a result of resection of the anal cushions, which act as the final mucosal barrier. Similar to sphincterotomy, rectal sensory innervation can be disrupted, and injury to the internal sphincter can occur during sharp dissection (68,69).