**5. Surgical treatment of chronic anal fissure**

Traditionally, lateral internal sphincterotomy (LIS) has been the gold-standard treatment for chronic anal fissure [38]. This technique decreases the pressure caused by the internal anal sphincter hypertonicity, normalizes the perfusion on the anoderm, alleviates the pain, and promotes fissure healing [3] (**Figure 4**). With trends toward topical agents and botulinum toxin injection, several studies have been conducted to compare the outcomes of these treatment methods [39–42]. A randomized controlled trial by Mentes et al. has revealed that LIS is superior to botulinum toxin injection regarding healing and recurrence in the long term [43]. Similar results have been obtained by Arroyo et al., 1-year healing rates with botulinum toxin and LIS were 45% and 93%, respectively [44].

#### **5.1 Techniques of lateral internal sphincterotomy**

The main issue with LIS has been the risk of incontinence [45]. Garg et al. have reported incontinence rates as 14% during a follow-up of 2 years [46]. In this study, most patients complained of flatus incontinence (9%), followed by soiling/seepage (6%), incontinence to liquid stool (0.91%), and solid stool (0.63%).

Determining risk factors for incontinence after LIS include the history of vaginal delivery, female patients, anteriorly located fissures, age over 40–50, concomitant anorectal procedures (hemorrhoidectomy), and presence of incontinence in preoperative setting [46]. The effects of LIS on quality of life have been evaluated by using the Gastrointestinal Quality of Life Index (GQLI) and the Fecal Incontinence Quality of Life Scale (FIQLS) in a 1-year follow-up [47]. Moreover, GQLI scores have significantly improved after LIS, and only three patients (1.2%) experienced deterioration in FIQLS scores.

**Figure 4.** *Healing of the chronic anal fissure. a) Preoperative image, b) postoperative 6-month image.*

Although LIS has been performing for over decades, there has not been a standardized technique, and with increased reporting of incontinence, the search for optimal sphincterotomy regarding the level and degree of sphincter division has commenced. In the following sections, variations in sphincterotomy techniques will be discussed.
