In a healthy adult without inflammatory bowel disease or prior anorectal surgery, how much resting (internal anal sphincter) and squeeze (external anal sphincter) pressure is lost after a low trans‑sphincteric fistulotomy, and how much can be recovered with pelvic‑floor rehabilitation?

Baseline Pressure Loss and Recovery After Low Transsphincteric Fistulotomy

Immediate Pressure Loss from Fistulotomy

Low transsphincteric fistulotomy causes a 25-30 mmHg reduction in resting pressure (internal anal sphincter function) and a 20-25 mmHg reduction in squeeze pressure (external anal sphincter function), with resting pressure showing greater impairment than squeeze pressure. 1, 2, 3

Quantified Pressure Changes

Resting Pressure (Internal Anal Sphincter):

• Baseline normal values: 80-85 mmHg 1, 2
• Post-fistulotomy values: 56-60 mmHg 1, 2
• Absolute loss: 25-29 mmHg (approximately 30-35% reduction) 1, 2

Squeeze Pressure (External Anal Sphincter):

• Baseline normal values: 120-165 mmHg 1, 2
• Post-fistulotomy values: 97-160 mmHg 1, 2
• Absolute loss: 20-24 mmHg when sphincter is divided (approximately 15-20% reduction) 2
• Notably, squeeze pressure may remain unchanged if sphincter-preserving techniques are used 2

Anatomical Extent of Sphincter Division

• A median of 41% of external anal sphincter length and 32% of internal anal sphincter length is divided during low transsphincteric fistulotomy 4
• Division of over two-thirds of the external anal sphincter is associated with the highest incontinence rates 4
• The functional anal canal length decreases from 4.12 cm to 3.74 cm when sphincter is divided 2

Pressure Recovery with Pelvic Floor Rehabilitation

The evidence shows minimal to no spontaneous recovery of baseline pressures after fistulotomy, and there is no high-quality data demonstrating that pelvic floor rehabilitation can restore lost sphincter pressures to pre-operative levels. 1, 2, 3, 5

Critical Evidence on Recovery

• At 3-month follow-up, resting pressure remains significantly reduced (56-60 mmHg) with no documented return toward baseline 1, 2
• At 12-month follow-up, pressure deficits persist without meaningful recovery 1, 4
• The pressure loss is permanent because it reflects structural sphincter division and fibrotic scar tissue formation, not reversible muscle dysfunction 3, 5

Why Rehabilitation Has Limited Effect

• The sphincter damage is anatomical (muscle division and defects visible on endoanal ultrasound) rather than functional weakness amenable to strengthening exercises 3
• Endoanal ultrasound shows internal anal sphincter defects increase from 30.8% to 74.3% of patients post-surgery, and external anal sphincter defects increase from 15.9% to 32.4% 3
• These structural defects cannot be reversed with pelvic floor exercises 3

Clinical Implications for Continence

Despite permanent pressure loss, 49-80% of patients develop some degree of incontinence symptoms, though most cases are mild (soiling, flatus incontinence) rather than frank fecal incontinence. 1, 3, 4

Incontinence Rates by Severity

• Soiling only: Common, affecting a minority of symptomatic patients 1
• Flatus incontinence: Most common symptom, occurring in the majority of symptomatic patients 1
• Liquid stool incontinence: Less common, affecting approximately 13% of symptomatic patients 1
• Solid stool incontinence: Rare in low transsphincteric fistulotomy 1, 4

Risk Factors for Worse Outcomes

• Low preoperative voluntary contraction pressure is an independent predictor of postoperative incontinence 1
• Multiple previous drainage surgeries significantly increase incontinence risk 1
• Division of >67% of external anal sphincter correlates with highest incontinence rates 4
• Active proctitis or rectal inflammation worsens healing and functional outcomes 6

Critical Pitfalls to Avoid

• Never perform cutting setons, which cause progressive sphincter transection and result in 57% incontinence rates 6, 7, 8
• Avoid repeat fistulotomy in patients with prior sphincter division, as this causes catastrophic incontinence 7, 8
• Do not assume pressure loss is temporary or reversible—counsel patients preoperatively that sphincter function changes are permanent 3, 5
• Recognize that "low" transsphincteric fistulas still involve significant sphincter muscle and carry meaningful incontinence risk 4

Alternative Approaches to Preserve Function

For patients at high risk (low preoperative squeeze pressure, prior fistulotomy, anterior fistula in women), sphincter-preserving techniques should be used instead of fistulotomy. 6, 7, 8

• Non-cutting seton drainage achieves 13.6-100% closure rates without additional sphincter division 6, 7
• Endorectal advancement flap is appropriate for patients without active rectal inflammation 6
• LIFT procedure may be considered as second-line sphincter-preserving treatment 7