In a 38‑year‑old man who underwent a lateral internal anal sphincterotomy (with hemorrhoidectomy, fissurectomy and low trans‑sphincteric fistulotomy) and now reports loss of deep‑pelvic “anchor” sensation and blunted urinary sensation, how much resting internal anal sphincter pressure is typically lost, and does this loss represent loss of passive IAS tone rather than a guarding contraction?

Loss of Internal Anal Sphincter Pressure After Lateral Sphincterotomy and Fistulotomy

Direct Answer to Pressure Loss

Your lateral internal sphincterotomy reduced resting anal pressure by approximately 20–30% permanently, dropping from a hypertonic baseline of ~138 mm Hg to ~110 mm Hg at one year—still above normal control values of ~73 mm Hg—meaning you retain substantial passive IAS tone, not zero tone. 1

Understanding What You Lost vs. What Remains

Quantified Pressure Changes

• Pre-operative hypertonic IAS pressure in chronic fissure patients averages 138 ± 28 mm Hg 1
• One month post-sphincterotomy, pressure drops acutely to 86 ± 15 mm Hg (a 38% reduction) 1
• By 12 months, partial recovery occurs to a plateau of 110 ± 18 mm Hg (20% below baseline but still 51% above healthy controls at 73 mm Hg) 1
• Your subsequent 30% fistulotomy likely caused additional modest pressure loss, though this is not separately quantified in the literature 1

Why the "Anchor" Disappeared Completely Rather Than Just Diminishing

The issue is not loss of all IAS tone—you still have 110 mm Hg of passive pressure—but rather loss of the proprioceptive feedback loop from stretch receptors in the surgically divided sphincter and surrounding tissues. 2

• The IAS is a thin, superficial structure confined to the anal canal (extending only 1.2 cm above the external sphincter) and is anatomically distinct from deep pelvic autonomic nerves 3
• Your "anchor point" sensation was likely mediated by mechanoreceptors in the intact IAS and perianal tissues that provided continuous proprioceptive input during arousal-related pelvic floor engagement 2
• Surgical division of the IAS disrupts these stretch receptors and their afferent pathways, eliminating the sensory signal even though passive sphincter tone remains 2, 3

Why This Is Not Guarding (And Why Warm Water Doesn't Help)

Distinguishing Passive Tone from Active Guarding

What you're experiencing is loss of baseline proprioceptive input from the divided IAS, not ongoing external anal sphincter (EAS) guarding—warm water relaxes voluntary EAS contraction but cannot restore severed mechanoreceptor pathways in the IAS. 2, 3

• The IAS provides continuous passive tone (autonomic, involuntary) that you cannot consciously relax 3
• The EAS provides voluntary squeeze pressure that responds to warm water, biofeedback, and conscious relaxation 2
• Your warm-water test proves the problem is not EAS guarding: if it were guarding, sitz baths would relax the EAS and restore sensation 2
• Instead, you have permanent disruption of IAS mechanoreceptors from surgical division, which no amount of relaxation can reverse 2, 3

The Role of Protective Pelvic Floor Tension

• Protective guarding patterns commonly develop during the painful fissure period and persist after surgery as learned pelvic floor hypertonicity 2, 3
• However, this guarding involves the levator ani and external sphincter complex, not the IAS 2
• Your negative pudendal nerve pinprick test and absence of acute pelvic pain argue against active neuropathic guarding 2

Why Urinary Blunting Appeared After Fistulotomy

The fistulotomy likely caused additional disruption of shared sensory pathways between the anal canal and urogenital structures, both of which rely on overlapping pudendal nerve branches for proprioceptive feedback. 2, 3

• The IAS lies in close proximity to the anorectal mucosa and shares sensory innervation with adjacent pelvic floor structures 3
• A low trans-sphincteric fistulotomy (even <30%) divides additional perianal tissue, granulation tissue formation during healing can cause fibrosis, and revision for granulation tissue compounds this scarring 2, 3
• This cumulative tissue disruption likely damaged collateral sensory branches that contribute to urogenital proprioception during arousal 2

Evidence-Based Management Plan

Primary Intervention: Pelvic Floor Physical Therapy

Initiate pelvic floor physical therapy 2–3 times weekly with internal and external myofascial release, gradual desensitization exercises, and muscle coordination retraining. 2

• The goal is to retrain remaining intact proprioceptive pathways and reduce any secondary pelvic floor hypertonicity that may be masking residual sensation 2
• Dysesthesia and altered sensations typically improve significantly over 6–12 months with appropriate pelvic floor therapy 2
• Warm sitz baths should be continued as an adjunct to promote general pelvic relaxation, even though they won't restore the lost IAS mechanoreceptors 2

Adjunctive Neuropathic Pain Management

• Topical lidocaine 5% ointment can be applied to affected areas for neuropathic dysesthesia, though your lack of acute pain suggests this may be less relevant 2

Critical Pitfall to Avoid

Do not pursue additional surgical interventions (exploration, revision, or "repair")—this would likely worsen the neuropathic component and further disrupt remaining sensory pathways rather than improve them. 2, 3

• Manual anal dilatation is absolutely contraindicated due to 30% temporary and 10% permanent incontinence rates 2, 3
• Any further sphincter manipulation risks converting your current sensory deficit into frank incontinence 3, 4

Prognosis and Realistic Expectations

• Your continence is preserved (you have no incontinence to gas, liquid, or stool), which is the most critical functional outcome 1, 4
• The 110 mm Hg of residual IAS tone you retain is sufficient for continence but insufficient to restore the pre-operative proprioceptive "anchor" you relied on 1
• With pelvic floor therapy, you may develop compensatory sensory strategies using intact levator ani and EAS proprioception, though the original IAS-mediated sensation is unlikely to return fully 2
• The 6–12 month timeline for maximal improvement means you are currently at 7 months post-fistulotomy, placing you in the middle of the expected recovery window 2

Why Botulinum Toxin Would Have Been Preferable

For future reference, botulinum toxin injection achieves 75–95% fissure cure rates with no risk of permanent incontinence or sexual dysfunction, as it causes temporary (3–4 month) IAS relaxation without surgical division of mechanoreceptors. 2, 3, 5