Pudendal Nerve Disruption During Fistulotomy
Fistulotomy does not disrupt pudendal nerve fibers—the procedure divides sphincter muscle tissue, not neural structures. The pudendal nerve runs through the ischiorectal fossa and Alcock's canal, anatomically separate from the intersphincteric plane where fistula surgery occurs 1.
Direct Evidence on Neural Impact
A prospective study measuring pudendal nerve terminal motor latency (PNTML) in 33 patients undergoing anal fistula surgery found no change in nerve conduction on either the diseased side (ΔPNTML = 0.03 ± 0.40 ms) or healthy side (ΔPNTML = 0.06 ± 0.42 ms) postoperatively 1.
The presence of an infectious process in the ischiorectal fossa does not alter pudendal nerve conduction, nor does the surgical procedure itself 1.
A larger series of 120 patients undergoing fistula surgery confirmed that pudendal nerve latency showed no postoperative change and did not differentiate continent from incontinent patients 2.
Mechanism of Incontinence After Fistulotomy
Continence disturbances after fistulotomy result from direct sphincter muscle division, not nerve injury 3, 2:
When approximately 30% of the external sphincter is divided during low transsphincteric fistulotomy, the median sphincter division is 41% of the external anal sphincter and 32% of the internal anal sphincter 3.
Post-fistulotomy incontinence correlates directly with the length of sphincter muscle divided, not neural damage—division of over two-thirds of the external sphincter produces the highest incontinence rates 3.
Endoanal ultrasound demonstrates that sphincter defects increase from 15.9% to 32.4% for the external sphincter and from 30.8% to 74.3% for the internal sphincter after fistula surgery, with corresponding decreases in anal canal pressures 2.
Clinical Implications
The 10-20% risk of continence disturbances after low transsphincteric fistulotomy is entirely attributable to mechanical sphincter disruption, not pudendal neuropathy 4, 3.
Aggressive probing or dilation during fistula surgery causes permanent sphincter injury through direct tissue trauma, not through nerve damage 4, 5.
Zero pudendal nerve fibers are disrupted during a properly performed low transsphincteric fistulotomy that divides 30% of the external sphincter—the anatomical planes involved do not contain pudendal nerve branches 1, 2.