Progress in the surgical treatment of sacrococcygeal pilonidal sinus: a review

Abstract

Background:

A pilonidal sinus (PS) is an acquired disease resulting from recurrent infections and chronic inflammation. A PS involving the sacrococcyx is referred to as a sacrococcygeal PS (SPS). An SPS is a rare chronic infectious disease for which surgery is a good choice. The incidence of SPS has gradually increased worldwide in recent years. However, surgeons have not reached a consensus on the preferred surgical approach for SPS. The authors performed a systematic review and meta-analysis to analyze differences in the efficacy of different surgical approaches for the treatment of SPS.

Methods:

A systematic search was conducted in the PubMed database covering the period from 1 January 2003, to 28 February 2023. The primary outcome parameters were recurrence and infection. Finally, statistical analysis (meta-analysis) was carried out using RevMan 5.4.1 software. In addition, we systematically reviewed the latest progress in the surgical treatment of SPS over the past 20 years, especially as reported in the past 3 years.

Results:

Twenty-seven articles, 54 studies, and 3612 participants were included in this meta-analysis. The recurrence rate following the midline closure (MC) technique was much higher than that of other techniques. Among the techniques analyzed, the differences between MC and Limberg flap (LF), and between MC and marsupialization were statistically significant [P=0.0002, risk ratio (RR)=6.15, 95% CI 2.40, 15.80; P=0.01, RR=12.70, 95% CI 1.70, 95.06]. The recurrence rate of open healing was higher than that of the Karydakis flap (KF) technique, and the difference was statistically significant (P=0.02, RR=6.04, 95% CI 1.37, 26.55). Most of the results comparing MC with other techniques suggested that the former had a higher infection rate, and the difference between MC and LF was statistically significant (P=0.0005, RR=4.14, 95% CI 1.86, 9.23). Comparison between KF and LF, modified LF and KF showed that the differences were not statistically significant in terms of recurrence and infection (P≥0.05).

Conclusions:

There are various surgical treatment options for SPS, including incision and drainage, excision of diseased tissue with primary closure and secondary healing, and minimally invasive surgery. It is still not possible to determine which surgical technique should be considered the gold standard for treatment, as even the results of different researchers using the same operation method are conflicting. But what is certain is that the midline closure technique has a much higher incidence of postoperative recurrence and infection than other techniques. Therefore, the anorectal surgeon should formulate the most suitable individualized plan for the patient based on a comprehensive evaluation of the patient’s wishes, appearance of the SPS, and the professional ability of the surgeon.

Highlights

• There are many therapeutic methods about sacrococcygeal pilonidal sinuses (SPS) and the best treatment is still controversial.

• There are few randomized controlled trials on the surgical treatment of the SPS.

• The midline closure technique for the treatment of the SPS should be abandoned.

• Surgeons should formulate individualized plans according to patient conditions.

A pilonidal sinus (PS), also known as a pilonidal cyst, is an acquired disease resulting from recurrent infections and chronic inflammation¹. A PS can occur in the sacrococcygeal region, penis², umbilicus³, breast⁴, or the head and face⁵. Because a PS tends to occur in the soft tissues of the sacrococcygeal intergluteal fissure, a PS involving the sacrococcyx is referred to as a sacrococcygeal pilonidal sinus (SPS). Mayo⁶ first described an SPS in 1833, but it was not until 1880 that the “hairy sinus” was officially named by Hodges⁷. For more than 100 years, many scholars have been arguing about the true cause of the disease. Even now, the pathogenesis of the SPS is still unclear, and there are two main hypothetical theories—the congenital theory and the acquired theory⁸. At present, the acquired theory is widely accepted by scholars. The theory proposed by Bearley believes that the pathogenesis of SPS can be divided into two parts, which appear sequentially. The first is the formation of penetrating sinus tracts, followed by aspiration sinus tracts⁹. Karydakis proposes three major factors contributing to PS disease: damaged skin, loose hair, and inward attraction¹⁰. Most studies have confirmed that even after radical surgical treatment of an SPS, there remains a certain probability of recurrence after surgery, which provides a supplementary verification of the acquired theory.

The incidence of SPS is ~26/100 000 in the United States¹¹, affecting ~70 000 people every year¹. The incidence of SPS in Germany is ~48/100 000¹². From 2005 to 2017, the hospitalization rate for SPS patients in Germany increased by nearly one-third, with regional differences in incidence¹³. An SPS most commonly occurs in adolescent or young adult males, with a male-to-female ratio of approximately 4:1¹⁴. The risk factors for SPS mainly include obesity, sedentary lifestyle, excessive body hair, family history, and poor hygiene habits¹⁵. In a recent study, oily and dark skin were also found to be risk factors for the development of an SPS¹⁶. In addition, in a retrospective study with a median follow-up time of 42 months, Li and colleagues used MRI to accurately measure the basic parameters (size, volume, position, surrounding tissue) of the SPS. It was found that MRI data can not only provide a choice of surgical approach, but also can be used to assess risk factors for postoperative complications and recurrence¹⁷. Unfortunately, only two flap techniques—Limberg flap (LF) and Karydakis flap (KF)—were used in this study, and the applicability of this conclusion to other flap techniques remains to be studied. The incidence of SPS is very low in China, which may be due to the fact that there are few studies on SPS and an incomplete understanding, which increases the probability of a missed diagnosis. At present, there are no definite epidemiological data on the incidence of SPS in China, and analysis of risk factors for the incidence of SPS is also rare¹⁸. However, China is a country with a large population. In recent years, with the improvement in living standards, the prevalence of obesity has increased¹⁹. At the same time, with advances in technology, the need for computer-based office work has also increased, and thus the number of people engaged in sedentary work has also increased²⁰. Through literature review, we found that Chinese and English literature on SPS has gradually increased in recent years, reflecting the gradual increase in the incidence of the disease both at home and abroad^14,21. However, the relationship between this gradual increase in incidence and increased sedentary behaviour and increased BMI requires further investigation of control variables. Diagnosis of an SPS is first based on symptoms and signs, such as recurrent long-term attacks of acute or chronic sacrococcygeal abscess, accompanied by hair growing in the sinus ostium. However, SPS needs to be differentially diagnosed from common perianal diseases, such as perianal abscess, anal fistula, infectious furuncle, carbuncle, and inflammatory bowel disease^1,22.

In this article, we report the findings of a meta-analysis of randomized controlled trials of different surgical approaches for the treatment of SPS over the past 20 years. At the same time, we searched for “pilonidal sinus” and “pilonidal cyst” in the PubMed database, and we introduce, summarize, and analyze the research involving SPS surgical treatment over the past 20 years, with a particular focus on articles from the past 3 years.

Materials and methods for meta-analysis

Search strategy

The following English-language database was searched systematically by the author: PubMed for clinical trials published from 1 January 2003 to 28 February 2023, using the following terms: ((((((“Pilonidal Sinus”[Mesh]) OR (Sinus, Pilonidal[Title/Abstract])) OR (Pilonidal Cyst[Title/Abstract])) OR (Cyst, Pilonidal[Title/Abstract])) OR (Cysts, Pilonidal[Title/Abstract])) OR (Pilonidal Cysts[Title/Abstract])) AND (((“Clinical Trial” [Publication Type])) OR (Intervention Study[Title/Abstract])).

Study inclusion and exclusion

Inclusion criteria

Randomized controlled trials including at least two surgical procedures for the treatment of SPS; results of clinical trials reporting postoperative recurrence or infection, with data for each outcome based on the longest follow-up in the study.

Exclusion criteria

PS in the non-sacral region of the study subject; no full text, or data missing or even wrong; acute SPS.

Data extraction

The author extracted information for meta-analysis. Extracted information: first author’s name, publication year, patient number, surgical approach, and the number of patients with postoperative recurrence or infection. Disagreements were settled through discussion until a consensus was reached.

Quality assessment

The risk of bias of the studies included in the systematic review was independently assessed by two reviewers using the Cochrane Collaboration Risk of Bias Tool²³. Each reviewer independently reviewed titles, abstracts, and full texts. Conflicts were resolved by consensus during discussion of the abstract and full review. The Cochrane Collaboration tool was used to assess seven aspects of study quality (random sequence generation, allocation concealment, blinding (participants and personnel), blinding of outcome assessment, incomplete outcome data, selective reporting, and other forms of bias). Low, unclear, or high risk of bias was assigned to each item.

Statistical analysis

First, all research data in the article were processed using Review Manager (RevMan) version 5.4.1. Second, we examined the heterogeneity between studies using the I² statistics. I² values above 50% were considered as markers of substantial heterogeneity²⁴. Therefore, a fixed-effect model was applied for comparisons with negligible heterogeneity (I² <50%). Otherwise, the random-effect model was used. Finally, we recorded the P value and risk ratio (RR) of the statistical results of the meta-analysis of dichotomous variables, as well as the corresponding 95% CI. The results are shown as a forest plot. A P value less than 0.05 was considered statistically significant.

Results

Study selection and characteristics

A total of 132 articles were identified from the PubMed database in the specified period using the above-mentioned subject words and free words. After reading the titles and abstracts, 81 articles whose topics were not relevant to this study were excluded, as well as seven articles with no control group, and 15 articles with uncommon procedures. We further excluded one article with incorrect original data and one article involving acute SPS patients after reading the full text. In the end, a total of 27 articles, 54 studies, and 3612 participants were included in this meta-analysis (Fig. 1)^8,25–50. The bias of the articles was assessed using the Review Manager program (RevMan 5.4.1) according to the Cochrane tool (Fig. 2).

Figure 1.

Flowchart for searching and identifying eligible studies.

Figure 2.

Risk of bias summary (“+” low risk of bias, “empty box” unclear risk of bias, “−” high risk of bias).

Results for postoperative recurrence and infection

In this meta-analysis, we evaluated the recurrence and infection rate following the use of different surgical methods in the treatment of SPS according to the inclusion criteria. A total of 27 articles, 54 studies, and 3612 subjects were included. Statistical data were subjected to a meta-analysis, and the results showed that only a few studies produced results that were statistically significant (P<0.05). The included randomized controlled trials mostly used the LF and KF techniques as well as modified techniques (with 19 and 12 studies, respectively). However, randomized controlled trials of minimally invasive treatments were rare (only two studies) (Table 1). The authors conducted forest plot analysis on statistically significant and common surgical procedures (the number of studies included in the comparison of different surgical methods ≥3).

Table 1.

Summary meta-analysis results for recurrence and infection.

Outcome	Comparison	Sample size	No. studies	I 2 (%)	P value	Meta-analysis RR (95% CI)
Recurrence	MC vs. LF	553	5	7	0.0002	6.15 (2.40–15.80)
	MC vs. KF	108	1	—	—	—
	MC vs. MLF	60	1	—	0.20	4.00 (0.47–33.73)
	BCL vs. VAAPS	286	2	0	0.86	1.05 (0.16–1.81)
	KF vs. PPC	96	1	—	0.47	1.84 (0.35–9.58)
	KF vs. LF	627	4	38	0.91	0.97 (0.51–1.83)
	OH vs. KF	321	1	—	0.02	6.04 (1.37–26.55)
	OH vs. LF	142	2	83	0.98	1.06 (0.02–74.52)
	MLF vs. KF	427	3	57	0.51	0.63 (0.16–2.50)
	LF vs. BCL	122	1	—	0.50	3.00 (0.12–72.23)
	MKF vs. MLF	120	1	—	0.57	0.50 (0.05–5.37)
	LF vs. MLF	272	2	0	0.07	3.66 (0.91–14.79)
	MC vs. OH	511	3	0	0.60	1.22 (0.59–2.53)
	MC vs. MA	142	1	—	0.01	12.70 (1.70–95.06)
Infection	MC vs. LF	460	4	0	0.0005	4.14 (1.86–9.23)
	MC vs. KF	116	1	—	0.13	9.63 (0.53–174.93)
	MC vs. MLF	60	1	—	0.06	4.00 (0.92–17.30)
	BCL vs. VAAPS	145	1	—	0.12	5.51 (0.66–45.98)
	KF vs. PPC	96	1	—	0.13	0.46 (0.17–1.25)
	KF vs. LF	727	5	47	0.07	1.64 (0.96–2.79)
	OH vs. KF	321	1	—	0.05	0.06 (0–1.02)
	OH vs. LF	146	2	70	0.80	1.33 (0.14–12.56)
	MLF vs. KF	435	3	0	0.61	0.81 (0.37–1.80)
	LF vs. BCL	122	1	—	0.75	1.20 (0.39–3.72)
	MKF vs. MLF	120	1	—	0.65	0.67 (0.12–3.85)
	LF vs. MLF	272	2	79	0.70	1.72 (0.10–28.43)
	MC vs. OH	457	2	0	0.47	0.82 (0.49–1.40)
	MC vs. MA	142	1	—	0.13	9.51 (0.52–173.50)

BCL, Bascom cleft-lift; KF, Karydakis flap; LF, Limberg flap; MA, marsupialization; MC, midline closure; MKF, modified Karydakis flap; MLF, modified Limberg flap; OH, open healing; PPC, partial primary closure; RR, risk ratio; VAAPS, video-assisted ablation of pilonidal sinus.

Postoperative recurrence

In terms of recurrence after SPS surgery, our meta-analysis showed that the recurrence rate following surgery using the midline closure technique was much higher than that of other techniques (MC vs. LF, MC vs. modified LF (MLF), MC vs. OH, MC vs. MA). Among them, the differences between MC and LF, and between MC and MA were statistically significant (P=0.0002, RR=6.15, 95% CI 2.40, 15.80; P=0.01, RR=12.70, 95% CI 1.70, 95.06, Fig. 3 and Fig. 4). Although the results of MC vs. OH were not statistically significant, MC still had a higher risk of recurrence (P=0.60, RR=1.22, 95% CI 0.59, 2.53, Fig. 5). However, the recurrence rate of OH was higher than that following surgery using the KF technique, and the difference was statistically significant (P=0.02, RR=6.04, 95% CI 1.37, 26.55, Fig. 6). In the meta-analysis of four comparative studies of KF and LF, although the results were not statistically significant, the former had a slight advantage in reducing disease recurrence (P=0.91, RR=0.97, 95% CI 0.51, 1.83, Fig. 7). Interestingly, in pooling three studies comparing MLF with KF, MLF showed a lower recurrence rate, but again this reduction was not statistically significant (P=0.51, RR=0.63, 95% CI 0.16, 2.50, Fig. 8).

Figure 3.

Forest plot of MC vs. LF using a fixed-effect model, outcome: recurrence. MC, midline closure; LF, Limberg flap.

Figure 4.

Forest plot of MC vs. MA using a fixed-effect model, outcome: recurrence. MA, marsupialization; MC, midline closure.

Figure 5.

Forest plot of MC vs. OH using a fixed-effect model, outcome: recurrence. MC, midline closure; OH, open healing.

Figure 6.

Forest plot of OH vs. KF using a fixed-effect model, outcome: recurrence. KF, Karydakis flap; OH, open healing.

Figure 7.

Forest plot of KF vs. LF using a fixed-effect model, outcome: recurrence. KF, Karydakis flap; LF, Limberg flap.

Figure 8.

Forest plot of MLF vs. KF using a random-effect model, outcome: recurrence. KF, Karydakis flap; MLF, modified Limberg flap.

Results for infection

In terms of postoperative infection in the SPS, the meta-analysis results showed that MC resulted in a lower infection rate compared with OH, but the difference was not statistically significant (P=0.47, RR=0.82, 95% CI 0.49, 1.40, Fig. 9). At the same time, comparisons of MC with other techniques all suggested a higher infection rate (MC vs. LF, MC vs. KF, MC vs. MLF, MC vs. MA). Among them, the results of four studies comparing MC and LF showed that the difference was statistically significant (P=0.0005, RR=4.14, 95% CI 1.86, 9.23, Fig. 10). In pooling five comparative studies of KF and LF, although the results were not statistically significant, KF had a higher risk of infection (P=0.07, RR=1.64, 95% CI 0.96, 2.79, Fig. 11). In pooling three studies comparing MLF with KF, MLF also showed a lower infection rate, but again the difference was not statistically significant (P=0.61, RR=0.81, 95% CI 0.37, 1.80, Fig. 12).

Figure 9.

Forest plot of MC vs. OH using a fixed-effect model, outcome: infection. MC, midline closure; OH, open healing.

Figure 10.

Forest plot of MC vs. LF using a fixed-effect model, outcome: infection. MC, midline closure; LF, Limberg flap.

Figure 11.

Forest plot of KF vs. LF using a fixed-effect model, outcome: infection. KF, Karydakis flap; LF, Limberg flap.

Figure 12.

Forest plot of MLF vs. KF using a fixed-effect model, outcome: infection. KF, Karydakis flap; MLF, modified Limberg flap.

Discussion

The treatment of SPS is mainly divided into non-surgical and surgical options. Non-surgical treatment, also known as conservative treatment, includes shaving or laser hair removal, antibiotics, phenol injection, fibrin glue, platelet-rich plasma, and traditional Chinese medicine treatments²². Surgical treatment mainly includes incision and drainage, excision of diseased tissue with primary closure, excision of diseased tissue with secondary healing, and minimally invasive surgery. The excision of diseased tissue with primary closure is divided into partial primary, transverse, midline, and off-midline closure. Off-midline closure mainly refers to various flap surgical procedures, including the KF, V-Y flap, Z-plasty, and other techniques and improvements based on these techniques. The excision of diseased tissue with secondary healing can be divided into open healing and marsupialization. Minimally invasive treatments include curettage, laser therapy, endoscopic adjuvant therapy, and radiofrequency ablation (Fig. 13)⁵¹. Although there are many surgical treatment options, the most appropriate surgical treatment for PS disease remains controversial^52,53.

Figure 13.

Logic diagram of surgical treatment of sacrococcygeal pilonidal sinus.

Incision and drainage

The main outcomes for incision and drainage are opening of the abscess septum in a simple way and provision of continuous unobstructed drainage. As an infectious disease, SPS is prone to a secondary acute infection with abscess formation. Most of the patients who seek treatment at the hospital have symptomatic infections. Incision and drainage of an acutely infected SPS with abscess formation is not controversial. An early observational study of simple incision and drainage noted the simplicity of incision and drainage. In the study, 58% of patients healed within 10 weeks and 21% relapsed, but the overall cure rate was only 76%¹. Some studies have reported that the recurrence rate following incision and drainage is as high as 40%⁵⁴. Approximately 60% of patients with a first occurrence of acute SPS can be cured after incision and drainage, but 40% of patients still need reoperation⁵⁵. Foreign objects, such as gauze, are sometimes used to pack the wound during incision and drainage, but studies have shown no difference in the recurrence rate after packing compared with no packing, thus the discomfort of wound packing can be avoided¹. Nevertheless, incision and drainage does not address the aetiology of a PS, which is often accompanied by a high recurrence rate and chronic sinus formation in patients after surgery. Therefore, further surgical resection is inevitable, especially for chronically infected PS. The optimal time between incision and drainage or lesion resection has not been determined.

Excision of diseased tissue with primary closure and secondary healing

After a diagnosis of chronic infectious SPS is confirmed, surgical resection or minimally invasive surgery should be performed. The former treatment option mainly includes excision of diseased tissue with primary closure and secondary healing. There is little difference between surgical resection and minimally invasive surgery. Specifically, the incision is designed according to the scope of the lesion, then lesions involving the cutaneous and subcutaneous tissues to the sacral fascia are completely removed, with the aim of removing all infected tissues. The last stage of the primary closure technique is to suture the wound. Secondary healing techniques involve open healing without incision manipulation or simple marsupialization at the skin edges of the incision. A meta-analysis in 2018 concluded that the recurrence rates for midline closure, off-midline closure, and open healing were 16.8%, 10%, and 17.9%, respectively, up to 5 years postoperatively. In addition, primary closure results in a more cosmetically acceptable wound than secondary healing, with a shorter healing time and reduced recovery time. Based on these data, researchers have suggested that midline closure and open healing techniques with high recurrence rates should be abandoned⁵⁶. At present, there is a general consensus to discontinue use of the midline suture technique^57–59 unless there is strong patient demand for aesthetic reasons. In 2019 a randomized controlled study which analyzed open healing and primary suturing of an SPS also reported that the recurrence rate following the midline suture technique was significantly higher than that following the off-midline suture technique⁶⁰. A subsequent meta-analysis of the postoperative recurrence rate of 3661 patients also confirmed that the midline suture technique had a higher recurrence rate, and the recurrence rate increased with increases in sample size, age, and follow-up time⁵². Another retrospective study in 2020 analyzed the use of primary transverse sutures to treat an uncomplicated SPS in children. The primary transverse suture technique also had a lower recurrence rate (12.5% vs. 37.5%), fewer complications, and less pain than open healing. This operation, however, will produce obvious scars which are difficult for many patients to accept⁶¹. Interestingly, in a 2021 retrospective study involving 133 adolescent patients, excision of diseased tissue with primary closure and secondary healing showed no significant difference with respect to recurrence rate, but the incidence of wound complications in secondary healing was lower. In addition, it was found that the recurrence rate and complications decreased with increasing age⁶². In another meta-analysis involving 3383 patients, it was concluded that open healing had a lower infection rate than primary suture⁵². In the most recent study, Albabtain et al. ⁶³ showed that the type of surgical incision closure was not related to overall recurrence in an experiment involving 369 patients, but primary closure was associated with early recurrence compared with secondary healing. This finding differs from the results of previous studies, which may be due to the different selection of research subjects, and some studies were limited by the limitations of electronic medical records. It is unknown whether patients underwent laser hair removal or other adjuvant therapy after surgery, which will affect the results. This issue needs to be verified by more standardized prospective randomized group studies. Excision of diseased tissue with partial primary closure of lesions is a technique that combines the excision of diseased tissue with primary closure and open healing. The incision is only partially closed, and the remainder of the incision undergoes open healing. In 2022, Yildiz²⁶ randomized 96 patients with SPS into two groups and treated the patients with different procedures, showing that excision of diseased tissue with partial primary closure had a significantly shorter wound healing time compared to the KF in a complex SPS (abscess or rupture), but there was no significant difference in other aspects. The application of this technique in acute SPS deserves further exploration.

Various skin flap techniques in off-midline closure

1. Bascom cleft-lift

In 1980, Bascom⁶⁴ described the Bascom cleft-lift technique for the first time. The brief procedure involves an oval incision to resect the skin and lesion and free the contralateral skin flap to flatten the gluteal groove. In 2020, Karim et al. ⁶⁵ randomly divided 60 patients with chronic SPS to undergo a Bascom operation or a simple excision of diseased tissue with primary suture for comparison. The Bascom operation group had lower infection (6.7% vs. 23.3%) and recurrence rates (3.3% vs. 16.7%). The pain was relieved and the wound healed better. A retrospective study in 2022 with a median follow-up time of ~8 years after Bascom surgery showed that the 10-year cumulative recurrence rate was only 27%, and the technique was safe enough for most patients⁶⁶. A recent survey on postoperative satisfaction found that 98.8% (494/500) of patients felt “very satisfied” or “satisfied” with the outcome after surgery⁶⁷.

2. Limberg flap

Also known as the rhomboid flap, the LF technique was first described by Limberg⁶⁸ in 1946. The brief operation process involves marking the lesion area with a diamond shape, completely resecting the lesion, including the sinus tract and infected tissue to the sacral fascia, and lifting and rotating the free diamond-shaped flap to cover the defect. In 2020, Gezer et al. ⁶⁹ conducted a retrospective study on 60 adolescent patients with an SPS. The results showed that findings achieved by the treatment of original, standardized LF excision is comparable with all of the treatment methods reported in the literature related with children. Compared with primary closure, this technique was found to have advantages of high patient satisfaction, fewer complications, and a lower recurrence rate, but the disadvantage was that number of research subjects using the LF technique was relatively small. Another systematic review and meta-analysis of randomized controlled trials in the same year concluded that the LF technique was superior to the Bascom technique, but the difference did not reach statistical significance⁷⁰. A subsequent retrospective study comparing LF surgery with KF surgery showed that the former had a statistically significant advantage with respect to postoperative complications and recurrence rates⁷¹. In a retrospective study in 2021, Danilov et al. ⁷² divided 117 patients with SPS into groups, then performed LF surgery and simple excision with suturing. The two groups showed significant differences in postoperative complications (3.2% vs. 14.5%) and recurrence rates (1.6% vs. 10.9%) respectively for the former and latter, but the length of stay and time to complete healing were both longer with the LF than with simple excision with suturing. Unfortunately, this study was a non-randomized grouping experiment, which may therefore have selection bias, thus more prospective randomized grouping studies are needed for further verification. The advantages of the LF technique were also verified in a cross-sectional study using this technique in the same year⁷³. A randomized group study by Maghsudi et al. ⁷⁴ further verified that the LF technique was superior to the simple primary suture and secondary healing techniques in many aspects; however, the LF technique took longer to perform. In 2022, Zubair et al. ⁷⁵ conducted an observational study on 46 patients with different clinical manifestations (single sinus, abscess, or ulceration) after LF surgery. Regardless of what type of SPS (chronic or acute infection), LF surgery was found to have advantages of a low recurrence rate and few complications (such as seroma, wound infection, and persistent pain). In the same year, Driouch et al. ⁷⁶ used this technique in patients with acute SPS and found that the effect was comparable to that in chronic PS, which once again verified the possibility of the application of this technique in an acutely infected SPS. This finding provides an additional option for the treatment of acute SPS, but more prospective studies are warranted.

3. Karydakis flap

In 1973 Karydakis⁴² first used the KF technique. The general surgical procedure is to make an oval incision of at least 1 cm beside the midline according to the condition of the lesion, completely resect the lesion to the sacral fascia obliquely, fully free the flap close to the midline, then pull the flap to the opposite midline and suture. The gluteal groove is thus flattened and covered with healthy skin, reducing hair intrusion, and reducing recurrence rates. In 2020 a prospective study on the use of the KF in 27 patients with an SPS showed that the technique had the characteristics of good wound healing and a low recurrence rate⁷⁷; however the study did not have a control group, the sample size was small, and the duration of follow-up was only 12 months. In the same year a retrospective study involving 112 patients who underwent Karydakis surgery reported a postoperative recurrence rate of 3.6% with an average follow-up duration of 28 months⁷⁸; unfortunately, this study also did not have a control group. In a retrospective study involving 61 adolescent patients with an SPS in 2021, the Karydakis technique proved to be more advantageous than excision of the lesion with secondary healing; the recovery time was shorter (37.77 vs. 107.76 days; P<0.001) and the recurrence rate was lower (4% vs. 28.6%; P=0.015). Therefore, the researchers suggested that the Karydakis surgical technique should be the first choice for the treatment of chronic SPS in the adolescent population⁷⁹. The study was a retrospective non-randomized subgroup study with a small sample size and the possibility of selection bias existed, which therefore needs to be further validated by prospective studies with larger sample sizes. A meta-analysis of 15 randomized controlled studies (1943 patients with SPS) was retrieved from a database the same year. There were no significant differences in the complication rate, healing failure rate, length of hospital stay, pain scores, or wound healing time for the KF compared to the LF. Although the former flap technique had a slightly higher incidence of seromas and wound infections, the former flap technique had a shorter return to work time and higher patient cosmetic satisfaction⁸⁰.

4. Keystone flap

The Keystone flap technique was first described by Behan et al. ⁸¹ in 2003 and applied to the treatment of skin cancer in various anatomic sites. The rationale for the operation is that the width of the designed flap is 1:1 compared with the width of the defect, the top angle of the flap adjacent to the defect is 90°, and the two ends of the outer bottom edge are designed as V-Y flaps. The final flap shape resembles a curved trapezoid, which can relieve longitudinal tension. In 2021, Calisir et al. ¹⁵ first applied this technique to the treatment of an SPS. The surgical design was similar to the original description and all lesions were resected to the depth of the sacral fascia. The study retrospectively analyzed the postoperative conditions of patients who underwent Keystone and LF surgeries. The results showed that the former had the advantages of low rates of wound dehiscence and necrosis, a short operative time, a short healing time, and a short return to work time. There was no significant difference between the two techniques in the recurrence rate within 1 year. The researchers believed that this technique could be an effective technique to replace the LF in SPS surgery; however, there were problems with the study; specifically, the grouping was not randomized and the follow-up time was short, thus more research is needed to further improve the technique.

5. Elliptical rotation flap

The elliptical rotation flap technique was first reported in 2004 by Nessar et al. ⁸² in the literature relevant to PSs. The flap is prepared from the skin, and the root of the flap is 1 cm wide. No recurrences were reported over a mean follow-up of 42 months postoperatively. Although no recurrences occurred, this may be related to the small sample size of 20 patients. This technique was subsequently refined by Dizen⁸³ and Omer et al. ⁸⁴ using oblique rather than vertical incisions, thereby reducing midline scar tissue formation. In a recent study, Gündoğdu et al. ⁸⁵ further modified this technique. The prepared flap is composed of subcutaneous fascia in addition to skin, and the width is the same as the widest distance of the resected flap, which is referred to as a subcutaneous fascia elliptical rotation flap. The study reviewed the relevant data of 149 patients who underwent surgery using this operative technique, and pointed out that this technique has a similar effect to the elliptical rotation flap in the case of less tissue resection. There was no recurrence after an average of 19 months of follow-up, and the investigators recommend it as the first choice for the treatment of a PS. The disadvantage of this study on the application of an elliptical rotation flap is that there was no control group. At present, there are few studies focusing on elliptical rotation flaps, and more complete prospective studies are needed to verify the efficacy of the elliptical rotation flap technique.

6. V-Y flap

The V-Y flap technique was first described in 1920 and has been used successfully as a triangular island flap. The main surgical procedure involves marking the lesion area and designing a V-shaped flap, then freeing the flap after completely resecting the lesion, pushing the flap toward the midline, suturing the flap, and finally creating a Y-shape⁸⁶. A retrospective study in 2017 showed that there was no significant difference in postoperative complication or recurrence rates between the V-Y and LFs, but the former flap technique required a longer hospital stay⁸⁷. In 2018 a retrospective study involving 61 patients with complex SPSs (lesions ≥10 cm or ≥1 sinus tract) showed that this technique has a low incidence of complications and no recurrences were detected in the early or late follow-up evaluation. Researchers believe that the V-Y flap technique can be used as an effective method for the treatment of complex SPSs⁸⁸. The study did not have a control group, and the selection of study subjects had possible selection bias. At the same time, reports on V-Y flap technology have been limited in recent years, thus this approach warrants further study.

7. Z-plasty

As early as the 1860s, Z-plasty was applied to treat PSs. The general procedure is as follows. First, a full-thickness longitudinal spindle resection of the lesion is performed in the centre of the PS. Then, a Z-shaped transfer flap is designed, and the two free flaps are rotated in opposite directions to cover the defect. Finally, the shape of the letter “Z” is formed after suturing⁸⁹. This technique rotates the long axis of the tissue, changes the direction of the scar, and increases the length of the skin in one direction. A retrospective randomized group clinical study in 2020 showed that Z-plasty resulted in fewer complications, shorter hospital stays, and lower recurrence rates at the short-term follow-up evaluation compared with excision alone, despite the longer operative time⁹⁰. A long-term study is needed to determine the recurrence rate, and there is a lack of comparison with other flap techniques. There are few reports about the latest progress using the Z-plasty technique.

Minimally invasive surgery

Traditional surgical excision is too aggressive for asymptomatic patients with an SPS because a cure can be achieved by improving sanitary conditions, laser hair removal, or minimally invasive surgery to improve patient satisfaction⁹¹.The development of minimally invasive surgical techniques in recent years also increases the available options for symptomatic patients with an SPS in addition to surgical resection.

Open and curettage under local anaesthesia for an SPS

The main procedure of this technique involves scraping off the sinus and all of the extensions after opening the sinus, removing all debris, hair, and granulation tissue, but keeping the fibrotic posterior wall of the sinus intact and trimming the edges of the skin. Finally, iodophor gauze is used to fill the wound. In 2015 Garg et al. ⁹² considered this technique to be an effective method for the treatment of simple and complex SPSs. The technique has the advantages of being a simple procedure, no hospitalization required, with a cure rate up to 97%, and resulting in only small scars. Although healing of the postoperative wound takes a long time, the daily work obligations of patients are not impacted, and the average 24-month follow-up recurrence rate is only 6.2%. In 2021 Garg et al. ⁹³ questioned the mainstream wide resection procedure; however, this may be because this technique is confused with simple incision and drainage of an abscess, which is effective in the early stage but has a high recurrence rate. There are few reports on the use of this technique. A later study increased the number of subjects to 111 and the median follow-up time was up to 38 months. The overall cure rate of this technique was as high as 98.1%, and the recurrence rate was only 3.7%. The researchers suggested that this technique be applied to the treatment of various types of SPS; however, the study did not have a control group and more research is needed for verification.

Pilonidal sinus laser-assisted closure (PiLAC)

In 2022 Johnson et al. ⁹⁴ reported a prospective study involving 35 patients with primary and recurrent SPSs treated with PiLAC. After long-term follow-up, the healing rate was found to be as high as 93% and the technique was recommended as an alternative to surgical resection. In the same year, a multicentre cohort study used PiLAC on 311 patients which showed that the technology had a high patient satisfaction rate, but the recurrence rate was 26% after a median follow-up time of 10 months⁹⁵. Although the current results are not definitive, the long-term recurrence rate should be verified. In another prospective study, Algazar et al. ⁹⁶ used a diode laser directly for the treatment of the SPS, an approach known as sinus laser closure (SiLaC). The investigators used the SiLaC technique and the LF technique to treat SPS patients. The results showed that SiLaC did not differ significantly from the LF technique in terms of healing rate and recurrence rate. However it was better in terms of operative time, length of hospital stay, and postoperative pain. Unfortunately, the cost of the technology is too high for many patients to afford. In addition, this study was a non-randomized controlled study, with a small sample size and short follow-up time. This still needs to be further verified by a large sample of randomized controlled trials.

Endoscopic pilonidal sinus treatment (EPSiT)

Meinero et al. ⁹⁷ first described EPSiT in 2014. EPSiT is a technique for the precise removal of hair, sinuses, and necrotic tissue under direct vision via small-incision endoscopy. In 2018 Tien et al. ⁹⁸ concluded, based on a systematic review, that patients who underwent EPSiT had a shorter recovery time, low short-term recurrence rate, and a high patient satisfaction rate. This technique, however, has high requirements for operating physicians, requires expensive equipment, and the long-term recurrence rate needs to be studied. A prospective study by Probst et al. ⁹⁹ in 2020 verified the advantages of this technique, although the sample size was relatively small. In the same year many researchers once again verified the advantages of EPSiT and suggested EPSiT as first-line treatment for SPS^100–103.

There have been few studies on PSs in children. A meta-analysis concluded that the PS recurrence rate is higher in children than adults¹⁰⁴. In 2021 Pérez-Bertólez et al. ¹⁰⁵ divided children with SPS into groups treated by excision of diseased tissue with primary suture, secondary healing, or EPSiT. EPSiT was found to have the advantages of quick recovery, pain relief, convenient wound care, and fewer complications; however, the number of patients in this study was small and the follow-up time was short, thus the recurrence rate needs to be further verified. In the same year a prospective study of negative pressure-assisted endoscopic pilonidal sinus treatment (NPA EPSiT) in 13 patients with SPS was conducted. NPA EPSiT has the advantages of less pain, fewer complications, a shorter hospital stay, and earlier resumption of daily activities¹⁰⁶. The disadvantages of research into NPA EPSiT include a small sample size and lack of a control group, which therefore needs further improvement and verification. Subsequently, a retrospective study analyzed 86 patients who underwent EPSiT and the recurrence rate was 1.2% after ~1 year of follow-up¹⁰⁷. Another retrospective study with a median follow-up of 12.8 months analyzed 152 children with SPSs who underwent EPSiT and had a recurrence rate of 4.6%¹⁰⁸. In the same year another retrospective single-centre study on EPSiT reported a recurrence rate of 12.5% with follow-up of 32 patients for an average of 22 months¹⁰⁹. The reported recurrence rates vary, which may be related to the different follow-up time and the small sample size of individual studies. The common problem is that most studies do not include control groups. In 2022 a review on the use of EPSiT in children concluded that the 30-month follow-up recurrence rate after EPSiT was ~1.6%. This technique was claimed to serve as the gold standard technique for SPS surgery in children, but further follow-up and more randomized controlled trials are needed for confirmation¹¹. In the same year laser treatment was combined with EPSiT. The results showed better wound healing, improved patient satisfaction, and reduced time to resume normal work. This finding will undoubtedly increase the cost, and the prospect of combining the two techniques needs to be verified by more randomized controlled studies^110,111. According to the latest Italian guidelines, EPSiT technology is regarded as the gold standard for the treatment of PS diseases¹¹². In the latest study, which is the first single-centre retrospective study in Australia, 13.5% of patients experienced post-healing recurrences after an average follow-up of 56.2 months¹¹³. In another retrospective study with a median follow-up of 49 months and a mean postoperative follow-up of 19 months, the postoperative recurrence rate was 15%. Although this recurrence rate was slightly higher than previous studies, the recurrence rate remained acceptable¹¹⁴. In a prospective non-randomized study involving patients with complex SPSs, by comparing the postoperative conditions of EPSiT and LF surgery, EPSiT was also shown to have a lower complication rate (11.5% vs. 26.5%). However, it was found that the success rate of the treatment was only 57.7% after an average of 27 months of follow-up, which was significantly lower than the 94.1% following LF surgery¹¹⁵. For complex SPSs, the two techniques each have their own advantages and disadvantages, and the choice should be made according to the patient’s condition. EPSiT is a newly emerging minimally invasive surgical technique. At present, long-term follow-up studies on this technique are rare, and further long-term studies with large sample sizes are needed to confirm the effects.

Video-assisted ablation of pilonidal sinus (VAAPS)

VAAPS and EPSiT were introduced at the same time in 2014. Milone et al. ¹¹⁶ first reported VAAPS. The process of this technique involves creating a fistula through a 0.5 cm circular incision using endoscopic forceps to remove hair and hair follicles under direct vision, then performing radiofrequency ablation of granulation tissue, and finally removing necrotic tissue. Because the operation is performed in the sinus tract, there is very little damage and patient satisfaction is very high. A 2019 retrospective study of 80 SPS patients compared VAAPS with traditional lesion excision techniques and found a significantly lower 5-year recurrence rate after VAAPS (7.5% vs. 25%), but no significant difference in terms of pain and patient satisfaction¹¹⁷. In 2020 Beamish et al. ²⁷ randomized 145 patients with SPS to either VAAPS or Bascom surgery. The 5-year follow-up evaluation showed that the long-term recurrence rates of the two groups were similar, and the satisfaction among VAAPS patients was higher. Subsequently, Beamish¹¹⁸ published a recognized comment on the results of this study in the International Journal of Surgery. In another retrospective study of patients with a recurrent SPS in 2021, the recurrence rates of patients treated using VAAPS 1, 3, and 5 years after surgery were 4.7%, 11.7%, and 23.07%, respectively. The researchers suggested that recurrent SPS can be treated by endoscopy¹¹⁹. The study did not have a control group. In the same year, in a study involving patients with acute SPSs and abscesses, the early use of VAAPS was shown to be more suitable for the treatment of acute SPSs than VAAPS after incision and drainage of the abscess. The 1-year, 3-year, and 5-year recurrence rates of the former technique were 4.9%, 10%, and 25%, respectively, and the cumulative postoperative recurrence rate was 14.6%¹²⁰. This long-term recurrence rate result is acceptable. Interestingly, in a recent retrospective analysis, Maione et al. ¹²¹ performed VAAPS on patients with complex (multiple external orifices, midline depressions, or the lowest external orifices ≥2 cm from the anal margin) or recurrent SPSs. The recurrence rates were 28.9%, 22.2%, and 38.1% 1, 3, and 5 years after surgery, respectively, and the cumulative postoperative recurrence rate was 65.8%. This extremely high recurrence rate is not consistent with previous reports and may be related to the small sample size or the selection criteria for study participants. Therefore, a large-sample, randomized, controlled study is still needed to further evaluate the effect of this technique in patients with complex or recurrent SPSs.

Gips trephination

The Gips trephination technique was first described and used by Gips¹²² in 2008. The Gips trephination technique is generally performed under local anaesthesia using a trephine (skin perforator) to excise the sinus tract and remove the hair, and finally washing the wound. During a mean follow-up of 6.9 years in 1358 patients, the Gips trephination technique was shown to be characterized by rapid healing and a low recurrence rate. The recurrence rates 1, 5, and 10 years postoperatively were 6.5%, 13.2%, and 16.2%, respectively. A retrospective study involving 105 patients with SPS in 2020 showed that the trephine excision technique resulted in fewer wound complications (3% vs. 20%) than the traditional wide excision technique, but the recurrence rate 4.6 months after the average follow-up (8% vs. 8.9%) was not significantly different¹²³. Further prospective studies are warranted to demonstrate the long-term results. In 2021 a retrospective study was performed in which one-half of the subjects were patients with recurrent SPSs; the results showed that Gips surgery was recommended for patients with simple and small SPSs. Compared with skin flap surgery, the Gips trephination technique has the advantages of easier implementation and teaching and a shorter healing time. The Bascom cleft-lift technique is considered for patients with complex and recurrent SPSs. The efficacy of this minimally invasive resection technique calls into question the use of extensive resection techniques¹²⁴. The sample size of this study was insufficient and the follow-up time was short, thus more research is still needed to verify the findings. Another retrospective study the same year found that the technique achieved a recurrence rate of 16.1% within 6 months after surgery; however, the study only had 19 subjects and the postoperative follow-up time was short, so a long-term study with a large sample is needed for verification¹²⁵. In 2022 a retrospective study by Diéguez et al. ¹²⁶ verified the advantages of Gips surgery in children, but the short follow-up time was problematic. Subsequently, Gips et al. ¹²⁷ re-verified the superiority of trephination in a retrospective study with an average follow-up time of 7.2 years. There was no significant difference in the recurrence rate compared with wide excision surgery, and the researchers believed that this technique should be the first choice for the treatment of primary SPSs. Interestingly, in the same year a prospective study involving 203 adult patients with SPSs who underwent trephination showed that the recurrence rate was 33.07% during a mean follow-up of 31.1 months. The recurrence rate of 33% was difficult to recognize, but the recurrence rate after repeated surgery was only 4.6% and the overall cure rate was as high as 91.5%. Researchers suggest that the Gips trephination technique could also be used for the treatment of patients with recurrent SPSs¹²⁸. The shortcoming is that 30% of the study sample was lost to follow-up, and the long-term effect after repeated surgery needs further observation.

At present, research into the minimally invasive treatment of SPS is an intense area of interest. Minimally invasive treatments, such as EPSiT, VAAPS, and Gips trephination, are safe surgical methods. At least in the short term when compared with traditional surgery, the recurrence rate is equivalent and the wound area is small, which can yield a better cosmetic effect. Challenges remain with new technologies, including the high cost of minimally invasive equipment and long learning curves for surgeons. In addition, the difficulty of minimally invasive surgery is also increased when dealing with complex and large SPSs. Therefore, minimally invasive surgical techniques cannot completely replace traditional skin flap techniques, especially in some grassroots hospitals.

Summary

As a chronic infectious disease, an SPS is rarely life-threatening, but will bring long-term discomfort and embarrassment to patients. If it is not treated in time or treated poorly, it will enter a chronic course and affect the patient’s life, work, and interpersonal relationships. The further aggravation of the disease will necessitate more difficult treatment, and consequently the economic burden on patients will also increase^129,130. At present, there are many treatment options for SPS, both non-surgical and surgical, and various new technologies are emerging in an endless stream. However the best surgical method for treating SPS remains controversial and studies are inconclusive (Table 2). Through our meta-analysis of related articles on common surgical procedures, we point out that it is still uncertain which surgical procedure can completely replace the other surgical options. The data produced by different researchers are quite different, even opposite, and the results of meta-analysis comparing different surgical methods are mostly not statistically significant. However, what is certain is that the midline closure technique is much worse than other techniques in terms of postoperative recurrence and infection rates, and the application of this technique should be avoided as much as possible in clinical practice. At the same time, we also found that there are very few high-quality randomized controlled trials on the SPS, especially in the field of minimally invasive techniques. The gold standard approach would be a surgical method with a short operative time, with short or even no hospitalization, early return to work, few complications, and a low recurrence rate. Most current surgical modalities cannot simultaneously achieve these goals. The postoperative recurrence rate index of SPS is very important, and it is a current research hotspot. There are differences in the recurrence rates between different surgical methods or different geographic locations for the same surgical method, and more prospective studies with large samples and randomized groups are needed to provide further answers^131,132.

Table 2.

Curative effect of different surgical methods based on the literature.

Surgery	Sample size	Complication rate (%)	Recurrence rate (%)	Follow-up time	Document number
Incision and drainage	15	20	40	Median 38.7 months	54
Primary closure	68	51	17.6	Average 10.5 months	62
	493	—	5.6	≥18 months	22
Transverse closure	24	—	12.5	Median 6.3 months	61
Midline closure	—	24	67.89	≥240 months	52
	—	—	16.8	≥60 months	56
Off-midline closure	—	—	10	≥60 months	56
Bascom cleft-lift	30	6.7	3.3	Average 3 months	65
	158	—	27	Median 96 months	66
Limberg flap	62	3.2	1.6	Average 26 months	72
	46	24	2.1	Average 12 months	75
Karydakis flap	112	—	3.6	Average 28 months	79
	26	53.8	4	Average 4.6 months	80
Keystone flap	53	11	1.9	Average 17.6 months	15
Elliptical rotation flap	149	—	0	Average 19 months	85
V-Y flap	61	16	0	≥60 months	88
Z-plasty	34	8.8	0	Average 6 months	90
Secondary healing	65	23	10.8	Average 10.5 months	62
Open healing	—	—	17.9	≥60 months	56
Marsupialization	73	2.7	1.4	Median 47 months	22
Minimally invasive treatment
Open and curettage	111	—	3.7	Median 38 months	93
PiLAC	311	—	26	Median 10 months	95
EPSiT	86	—	1.2	Average 12 months	107
	152	—	4.6	Median 12.8 months	108
	32	—	12.5	Average 22 months	109
	137	—	13.5	Average 56.2 months	113
	26	11.5	26.9	Median 27 months	115
VAAPS	40	—	7.5	≥60 months	117
	41	—	14.6	≥60 months	120
	63	—	28.9	Average 12 months	121
Gips trephination	60	3	8	Average 4.6 months	123
	372	—	18.5	Average 86 months	127
	203	—	33.07	Average 31.3 months	128

”—“ indicates that it has not been reported.

EPSiT, endoscopic pilonidal sinus treatment; PiLAC, pilonidal sinus laser-assisted closure; VAAPS, video-assisted ablation of pilonidal sinus.

There are advantages and disadvantages among off-midline suture (various flap techniques), secondary healing, and minimally invasive surgical techniques. The recurrence rates among the three techniques are inconclusive based on current clinical research, but in an acceptable range. Therefore, we suggest that the choice should be made after a comprehensive evaluation of the patient’s condition, willingness, and the operator’s expertise in surgical methods. For children and adolescent patients, in the critical period of personality development, the mind is more fragile, the mood swings are relatively large, and they are more susceptible to the impact of the disease¹³³. Minimally invasive treatment involves a shorter hospital stay and less postoperative scarring, and thus can rapidly resolve the negative impact of the disease on young patients’ quality of life^17,134. Hence, EPSiT, VAAPS, and Gips trephination can be used as the preferred minimally invasive technique¹³⁵. For SPSs with large lesions that are difficult to treat with minimally invasive techniques, there is currently no clear difference in outcomes between various flap techniques; however, judging from the current research, we are of the opinion that the Bascom cleft-lift, LF, and KF techniques, which are widely used at present, can be used as the preferred treatment methods.

For this article we conducted a systematic review and meta-analysis of studies on the surgical treatment of SPSs over the past 20 years. At the same time, we introduced, summarized, and analyzed the techniques used, and elaborated especially on clinical trials carried out in the past 3 years. At present, relatively few surgical reports have been identified. Many reports of traditional classic surgical procedures have not been explored in randomized controlled studies. Especially for minimally invasive treatments, randomized controlled trials are very rare. Therefore, more prospective randomized clinical studies are needed to further verify their effects. Regardless of what surgical technique is used, prevention of risk factors for PS disease and standard postoperative wound care are essential. These approaches play a crucial role in the onset and recurrence of a PS^1,91.

Ethical approval

The manuscript is a review, so ethical approval is not application.

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Author contribution

P.W. and Y.Z.: conceptualization, writing—original draft; Y.Z.: revising; S.W.: conceptualization and editing; Z.F.: Writing—review and editing, supervision.

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Zhe Fan.