Thus, common complications such as anal incontinence, anal stricture and anal deformity are avoided. The one-time cure rate is more than 92%, and the average healing time is 22 d [11,13]. For patients with Crohn’s fistula and AIDS-associated fistula, long-term drainage and hanging can be used to limit symptoms and protect anal function. The rectal mucosal flap/perianal flap is used to close the internal orifice. Rectal mucosal flap pushing is one of the common methods to treat complicated fistulas [14]: After anesthesia, the path of the fistula and the internal orifice are explored. A semilunar or trapezoidal lingual mucosal flap is made approximately 0.5 cm below the internal orifice, which should include the mucosa, submucosa, and part of the circumferential muscle layer, with the base twice the width of the top, to ensure blood supply and tension-free. The lower edge of the mucosal flap is excised and the remaining mucosal flap is pulled down and intermittently sutured to the skin of the anal verge, with interrupted sutures to repair the internal sphincter. The external opening was left open for drainage. Uribe et al [15] reported 60 cases of anal fistula treated with rectal mucosal flap pushing with a follow-up of 43.8 mo. The recurrence rate was 7.1%, 12.5% mild anal incontinence and 9% severe anal incontinence. The second procedure did not increase the impairment of anal function. In a study by van der Hagen et al [17], the long-term recurrence rate of rectal mucosal flap mastication was 63%. The main difference is that the perianal flap is a flap of perianal skin, including subcutaneous fat and part of the internal sphincter of the anal canal, and the flap is pulled up with tension-free sutures to close the internal orifice. Jun et al [18] treated 40 cases of high anal fistulae with perianal flap mastication, with a 95% recovery rate, consistent with that reported by Hossack et al [19], with a healing time of 2-3 wk and no anal incontinence [20]. Zimmerman et al [21] reported a cure rate of 78% for perianal flap nudging for anal fistulas, with 30% of patients experiencing anal hypospadias. This method is suitable for high trans-sphincteric and supra-sphincteric fistulas with internal orifices at the dentate line, and also for anterolateral fistulas in women, with a success rate of 70%-75% for Crohn’s disease fistulas with well-controlled intestinal inflammation, and reoperation in patients who fail [22,23]. Hossack et al [19] concluded that perianal flap push closure of the internal orifice significantly improved the quality of life of patients and improved anal incontinence symptoms. Rectal mucosal flap mastication and perineal flap mastication for complex anal fistulae remove the infection, close the internal orifice without damaging the external sphincter, have a low risk of incontinence, are minimally invasive, avoid lock-eye deformities, and can be repeated [24]. The key to successful surgery is to ensure the blood supply to the mucosal flap or flap, and inadequate blood supply is the main cause of failure. Compared with the two, perineal flap nudging has more advantages: (1) it does not cause rectal mucosal, submucosal or muscular defects, avoiding the formation of infected dead space and damage to the flap; (2) good extensibility, avoiding tension sutures; (3) higher success rate and easier operation [25]. 2.Fibrin glue closure/anal fistula plugs The biggest advantage of fibrin glue closure over traditional fistula surgery is that there is no sphincter damage and no impact on anal function. After the inflammation of the fistula has subsided and the granulation around the straps is filled, the straps are removed, the canal is scratched, the length of the fistula is measured, and the internal opening is closed with 3-0 absorbable sutures. A thin tube for fibrin glue injection was introduced into the external orifice at the measured length, and the fibrin glue was injected, retracted while injecting, until the external orifice was closed [14].Sentovich initially reported a cure rate of 85% for fibrin glue treatment of anal fistula [26], but their long-term study found that the cure rate decreased to 69% [27]. Zmora et al [28] treated 60 anal fistulas with this method with a follow-up of 6mo and the cure rate was 53%, which is in line with the cure rates of 55% and 50% reported by Witte et al [29] and de Parades et al [30]. Despite the effectiveness of fibrin glue in the treatment of anal fistula, the long-term efficacy decreases to 16% over time [31,32]. The main reasons for the failure of fibrin glue treatment for anal fistulae are fibrin glue detachment and recurrence of fistulae due to incomplete removal of inflammatory tissue [33]. Anal fistula plug (AFP) is an absorbable biomaterial extracted from the submucosa of porcine small intestine, similar in structure to the human extracellular matrix, which stimulates and acts as a scaffold to help repair and reconstruct the damaged tissue. The method was as follows [34]: the internal and external openings of the fistula and the course of the ducts and branches were examined and drained for 8 wk so that the fistula and its branches could be adequately drained and the inflammation could subside. After the patient was anesthetized, the fistula was flushed with hydrogen peroxide, scraped and the external opening was excised. The AFP was inserted through the internal opening until it was securely fixed, and the AFP was intermittently sutured to the anal sphincter and the internal opening was closed. The excess AFP is trimmed around the external orifice, and the AFP is left open for drainage without fixation to the external orifice. The key to successful AFP is effective control of fistula inflammation, as inflammatory tissue can become a barrier to AFP as a scaffold to stimulate repair and reconstruction of damaged tissue, leading to treatment failure. Schwandner et al [34] treated 60 trans-sphincteric fistulas with AFP with a 62% recovery rate, consistent with other reports [35], and without the risk of anal incontinence. Johnson et al [36] compared the efficacy of AFP with that of fibrin glue and showed that AFP had a high cure rate. Of the 25 cases of complicated anal fistulae, 10 were in the fibrin glue group and 15 in the AFP group, with a follow-up of 13.8 wk. The cure rate was 20% in the fibrin glue group and 86.7% in the AFP group. However, recent studies have shown that the long-term cure rate of AFP ranges from 15% to 40% [37-39]. The cost of AFP is high and its effectiveness needs to be studied in the long term, and further studies are needed to determine whether postoperative dietary factors contribute to treatment failure [40]. The ligation of intersphincteric fistula tract (LIFT) was first proposed by Rojanasakul in Thailand [41] and differs from the method described by Matos et al [42]. The Matos method involves excision of the fistula between the sphincters, suturing the opening of the internal anal sphincter, excision of the fistula, and repair of the fistula. Compared with traditional fistulotomy or cutting and hanging, LIFT does not cut the anal sphincter and the postoperative function of the anus is intact. The method is as follows. The patient is prepared with the bowel before surgery and placed in a prone folding position after anesthesia. The fistula was isolated between the sphincter muscles, and the fistula was severed with sutures on each side near the internal and external sphincter muscles, and the fistula was repeatedly tested with hydrogen peroxide until it was confirmed to be completely ligated. The fistula from the severed end to the external opening was scraped with a spatula and the external opening was left open for drainage. Postoperative anti-inflammatory treatment with antibiotics such as ciprofloxacin and metronidazole is given, and the patient needs to clean the wound promptly after defecation [43]. The main reason why anal fistulas do not heal spontaneously is that fecal debris enters the fistula from the internal orifice and causes infection. LIFT is based on closure of the internal orifice and removal of the infected anal glands and is mainly indicated for trans-sphincteric and suprasphincteric fistulas and can be extended to almost all fistulas, but not for patients with early, incomplete fistulas [43]. Rojanasakul et al [41] treated 18 trans-sphincteric fistulas with LIFT with a 94.4% cure rate and a mean time to healing of 4 wk without anal incontinence, but they were optimistic about long-term recurrence. Shanwani et al [44] reported 45 cases of complex anal fistulas treated with LIFT with a cure rate of 82.2% without anal incontinence and a recurrence rate of 17.7% 3-8 mo after surgery. Aboulian et al [46] recently reported 25 cases of trans-sphincteric fistulas treated with LIFT, with a 68% recovery rate and no anal incontinence; one of the eight cases that failed was treated with LIFT again. The results of the study showed that LIFT has significant advantages over other surgical methods for the treatment of complex anal fistulas [41,44-46]: (1) complete preservation of the anal sphincter; (2) reduction of tissue damage and healing time; (3) small invasion; (4) simple operation and low cost; and (5) no obstacle to secondary surgical treatment after recurrence. As a new technique, the long-term clinical efficacy and postoperative function of the anal sphincter need to be further investigated. 4. Conclusion The risk of anal incontinence due to drainage ligatures is low, but the recurrence rate is high and there is a lack of fatty hinterland. The risk of anal incontinence due to rectal mucosal flaps, perianal flap nicks, fibrin glue and AFP for anal fistula is low, but the recurrence rate is relatively high and the operator’s technique is demanding. LIFT is a good solution to these problems, but its long-term clinical efficacy remains to be studied. No single technique can cure a complex anal fistula, and a comprehensive approach is needed to cure the fistula or reduce the symptoms while maintaining the function of the anal sphincter, so as to achieve the best results in the eradication of complex anal fistula and the preservation of anal function.