**8.1 Sphincter cutting procedures for low fistula**

Fistulotomy is the oldest, simplest, and most widely used procedure for anal fistulae. Most major guidelines recommend fistulotomy as a suitable and safe procedure for simple or low fistula [13, 25, 26]. This procedure involves laying open the entire fistula tract, together with the sphincter muscles it traverses, with adequate curettage to remove all granulation tissue tract [13, 31]. Marsupialization of the edges appears to speed up wound healing and reduces post-op pain and bleeding, but reported benefits were not significant [13]. Success rate is more than 90%, but incontinence rate is reported as high as 28% in elective setting [31]. According to Garg et al. in 2020, fistulotomy performed on low intersphincteric and low transphincteric fistulas (Garg's Classification grade 1 & 2) is safe. Post-operative mean continence score increased from 0.044 to 0.135, without reaching statistical significance. Low fistula is defined as involvement of less than 1/3 of external sphincter [18]. Failure of treatment or recurrence is associated with inappropriate selection of patients with high fistula or multiple tracts [31].

Internal sphincterotomy was first reported by Eisenhammer in 1966 to treat low intermuscular fistula (low intersphincteric type) which accounted for majority of cases in his series [2]. The principle is similar to fistulotomy, where the only difference is only lower half of internal sphincter muscles were laid open to eradicate intersphincteric sepsis. This technique gradually became synonymous with fistulotomy in various literatures as later studies showed that low intersphincteric type is far less common than low transphincteric type [7, 12]. In recent decade, ASCRS Practice Parameters introduced it as a treatment for intersphincteric fistulous abscess [13]. This technique is suitable for low intersphincteric type and does not cause incontinence [6].
