**5.1 Hybrid sphincter preserving techniques**

Hybrid sphincter preserving techniques are combinations of two or more sphincter preserving techniques in a single procedure to increase healing rates and achieving better results.

Several reports exist with different combinations of techniques with authors trying to achieve higher healing rates, but the majority of reports are on a single institution basis or case reports with a small number of patients.

A combination of VAAFT and LIFT techniques was performed with intention of secure closure of internal fistula opening from intersphincteric space and additional exploration and eradication of remaining fistula tract from external fistula opening with identification of possible secondary branches using fistuloscope [55, 56]. VAAFT was also used in different combinations with other sphincter preserving techniques such as FiLaC® procedure and with RAF procedure in cases with large internal fistula opening [38, 44, 57].

The combination of LIFT technique with the insertion of a bioprosthetic graft in intersphincteric space was also described in a study that included 31 patients, where the success rate was 94% in a one-year follow-up period [58]. Another study combined LIFT and human acellular dermal matrix as a bioprosthetic plug with a reported success rate of 95% on a 21-patient sample [59]. Rectal advancement flap with the injection of porcine dermal collagen implant through the external opening was combined in a study which included 24 patients with a success rate of 82.5% in a 14-month follow-up period [60].

It was to be expected that surgeons started to combine two or more sphincter preserving techniques to achieve better results, but until evidence is found that one technique, or combination of techniques, has significantly better results over the others, they should be tailored individually depending on patient's case.

#### **5.2 Fistulotomy with primary sphincter reconstruction**

This approach in the treatment of anal fistulas has the same operative philosophy as fistulotomy or fistulectomy, but is reserved for higher fistulas. In this procedure surgeon after eradication of the fistula tract and possible secondary fistula branches to prevent recurrences, makes additional anal sphincter reconstruction to try to eliminate the possibility of postoperative fecal incontinence. Ratto et al. reported a 93.2% overall success rate with a low morbidity rate using this approach. Overall postoperative fecal incontinence was 12.4% mainly post-defecation soiling, without significant changes in anorectal manometry parameters [61]. Voon et al. reported their experience in using this technique and had good outcomes with a very low rate of continence disturbance in follow-up period [34]. Even though this technique has been implemented in guidelines for anal fistula treatment by several surgical societies, it wasn't accepted worldwide as the standardized procedure [62]. In case of abscess formation as the initial presentation, it is crucial to place seton drainage to give enough time for maturing of the fistula and to prevent continence disturbance following fistulotomy.

## **5.3 Trans anal opening of the intersphincteric space (TROPIS)**

This technique was described and published by Garg, who used this approach in the treatment of high complex anal fistulas with a high primary healing rate and very low incidence of morbidities [8]. It is well known that high intersphincteric parts of anal fistula and abscesses are difficult to reach through intersphincteric approach or probing from external fistula opening, as well as that they are usually branching.

TROPIS approach also satisfies golden principles in the treatment of anal fistula such as identification and resolving internal fistula opening problem, as well as intersphincteric fistula tract with the accompanying anal gland, and also eradication of remaining fistulous tract by curettement.

The procedure is done by laying open intersphincteric space through internal anal with preservation of external sphincter. The external tracts in the ischioanal fossa should be curetted and the intersphincteric space is left open for secondary healing. In the initial prospective cohort which included 61 patients, the success rate was 84.6%

with no significant changes with continence. The study included patients with high transsphincteric (anterior and posterior) and high intersphincteric type of fistula [8].

TROPIS procedure is an excellent approach for posterior high transsphincteric type and high intersphincteric type of anal fistula, especially if transsphincteric fistula is located at the puborectalis level. However, combination with drainage (preoperative seton placement and postoperative drain placement in remaining tract from external fistula opening), curettement or excision of external tracts is necessary to reduce recurrences.

#### **5.4 Use of autologous platelet rich plasma in anal fistula treatment**

Autologous platelet rich plasma (APRP) is nowadays used in various fields of medicine such as orthopedics, plastic surgery, dental medicine, but also in the treatment of anal fistula in the last decade. APRP is platelet concentration derived from centrifuged full blood after removal of red blood cells. Such prepared plasma is a rich source of various growth factors implicated in regeneration and tissue healing [63, 64].

The procedure consists of curettement of fistula tract and closure of internal fistula opening with an additional injection of previously prepared platelet rich autologous blood sample [65]. The majority of publications combined mucosal advancement flap with APRP injection [65–67]. Several publications reported an average healing rate from 60 to 90% [40, 66–68]. The drawbacks of mentioned publications were that they had a relatively small number of patients enrolled and still no meta-analyses exist on the subject. No problem with any type of postoperative fecal incontinence was reported. This is still considered to be a somewhat experimental procedure and is not widely used. The platelet separation procedure requires special equipment that is often only available in larger institutions. Also cost per patient exceeds that of the other techniques, which is why this technique needs more solid evidence for a patient benefit before it can be considered to become one of the mainstream sphincters preserving treatments.
