Neither the IAS nor EAS is Directly Involved in Ejaculation
The external anal sphincter (EAS) has anatomical and physiological connections to the bulbocavernosus muscle that may create sensations during ejaculation, but neither the internal anal sphincter (IAS) nor the EAS plays a primary role in the ejaculatory mechanism itself. 1
Anatomical Relationship Between EAS and Sexual Function
The superficial fibers of the EAS base loop extend forward to the penile bulb, where they form the bulbocavernosus muscle (BCM), creating what has been termed the "anogenital muscle" 1. This anatomical continuity explains why:
- Glans penis stimulation causes synchronous contraction of both the EAS and BCM with similar latency and action potentials 1
- The muscle complex plays a dual role in both fecal control and sexual response 1
- When the EAS is anesthetized, both muscles fail to respond to glans stimulation 1
Clinical Implications for Post-Fistulotomy Patients
Understanding the Sensation
In patients who have undergone low transsphincteric fistulotomy, any altered sensations during ejaculation are likely due to:
- Pelvic floor muscle tension and protective guarding patterns that persist after anorectal surgery 2
- Neuropathic changes from surgical trauma rather than direct involvement of the sphincters in ejaculation 2
- The anatomical proximity and shared innervation between the EAS and bulbocavernosus muscle 1
The IAS Has No Role in Ejaculation
The internal anal sphincter is responsible for maintaining resting anal tone through involuntary smooth muscle contraction 3, and has no documented connection to sexual function or ejaculation. The IAS:
- Provides 70-80% of resting anal sphincter tone 4
- Functions independently of voluntary control 5
- Has no anatomical connection to the genital structures 1
Management Approach for Post-Surgical Sensory Changes
If a patient experiences altered sensations during ejaculation after low transsphincteric fistulotomy:
- Initiate pelvic floor physical therapy 2-3 times weekly with internal and external myofascial release, gradual desensitization exercises, and muscle coordination retraining 2
- Apply topical lidocaine 5% ointment to affected areas for neuropathic pain control 2
- Expect improvement over 6-12 months with appropriate therapy 2
Critical Pitfall to Avoid
Do not pursue additional surgical interventions, as this would likely worsen the neuropathic component rather than improve symptoms 2. The low transsphincteric fistulotomy itself carries minimal risk of continence issues when properly performed, with healing rates of 100% and no significant changes in incontinence scores at 6 months 6.