>>3088942> The text supported by Prolapse & Incontinence has been updated as well.
• Strong, repeated shear (frictional sliding) force in the anal canal is likely to permanently damage supporting tissue of the internal hemorrhoidal cushions at the least, leading to internal hemorrhoidal prolapse (progressively worsening with cumulative damage from repeated trauma). Damage to one or more of the internal hemorrhoidal cushions elicits no pain sensation due to their lack of somatic innervation. As healthy internal and external anal cushions help to maintain fecal continence with a watertight seal, anal canal deformation due to their disease or removal can result in fecal incontinence (FI). Furthermore, pulling or traction on nerves in the anorectal region can potentially lead to neuropathy and associated FI.
• Internal rectal prolapse (IRP), aka rectal intussusception, is a common finding among asymptomatic individuals. Strong, repeated shear force in the rectum probably does contribute to development of full-thickness external rectal prolapse (aka procidentia) particularly when IRP is present. Internal hemorrhoidal prolapse—among other conditions—also may contribute to rectal prolapse development. FI can be a consequence of rectal prolapse as well.
• Stretching the anal canal with girthy insertions is likely to disrupt or fragment one or both anal sphincter muscles, possibly without pain as the internal anal sphincter muscle also lacks somatic innervation. Such damage results in permanent muscle weakening and is associated with FI especially with a damaged or dysfunctional puborectalis muscle. Stretching the anal canal repeatedly with insertions of progressively increasing circumference may cause cumulative muscle damage.
• Trauma—including anoreceptive trauma—can instigate development of numerous other anorectal conditions that may lead to FI, such as a fistula. Additionally, surgical treatment for anorectal conditions can contribute to development of FI.
[Medical references: Prolapse & Incontinence]