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Clinical Application of Modified Karydakis Flap Procedure for Pilonidal Cyst: A 2-Year Single-Center Retrospective Cohort Study

This 2-year retrospective cohort study demonstrates that a modified Karydakis flap procedure incorporating an additional scalp needle drainage tube at the natal cleft significantly reduces postoperative seroma and wound complications, accelerates recovery, and lowers recurrence rates compared to the standard technique without increasing surgical trauma.

Original authors: Jianheng Wang, Qianqian Wang, Min Liu, Zhigang Zhang, Chunxiang Liu, Penglin Liu

Published 2026-07-21

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Jianheng Wang, Qianqian Wang, Min Liu, Zhigang Zhang, Chunxiang Liu, Penglin Liu

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body is a bustling city, and sometimes, even in the most well-planned neighborhoods, little problems pop up. One such problem is a "pilonidal cyst." Think of this as a tiny, angry burrow that forms in the deep valley between your buttocks (the natal cleft). It's like a hidden pocket where stray hairs get stuck, causing a buildup of dirt and bacteria that turns into a painful, recurring abscess. For years, doctors have known that the best way to fix this is to surgically remove the burrow and then stitch the skin back together in a way that flattens that deep valley, so the hair can't get stuck again. This specific stitching technique is called the "Karydakis flap." It's a bit like taking a piece of fabric from the side and pulling it over the middle to smooth out a wrinkle. While this method is great, it has a annoying side effect: after the surgery, fluid can sometimes get trapped in the empty space under the new skin flap, like water pooling in a hollowed-out tree trunk. This trapped fluid, called a "seroma," can cause infections, delay healing, and even make the cyst come back.

So, the big question for surgeons is: how do we make sure that "tree trunk" drains perfectly every time? A team of researchers at the Affiliated Hospital of Qingdao University decided to test a clever new trick. They took the standard Karydakis flap surgery and added a second, tiny drainage tube made from a special scalp needle. Think of the main drainage tube as a big vacuum hose sucking water out of the main room, while this new, tiny needle-tube acts like a straw placed right in the deepest, trickiest corner of the room to catch the last few drops that the big hose misses. They wanted to see if this "double-drainage" system could stop the fluid buildup, help patients heal faster, and keep the cyst from returning.

The Experiment: Testing the Double-Drainage Trick

The researchers looked back at the records of 122 patients who had surgery for this cyst between December 2022 and December 2024. They split them into two equal teams of 61 people each. One team got the "Standard" surgery, which uses just the one big drainage tube. The other team got the "Modified" surgery, which used the big tube plus that extra tiny scalp needle tube placed right in the center of the surgical site.

The results were pretty clear. The team with the extra tiny tube (the Modified group) had way fewer problems. Only 2 out of 61 patients in the Modified group developed a seroma (that's about 3.28%), compared to 11 out of 61 in the Standard group (18.03%). That's a massive drop! Because there was less fluid trouble, the Modified group also had fewer total wound problems, like the skin pulling apart or getting infected. In fact, the total rate of wound complications dropped from nearly 28% in the Standard group to just under 12% in the Modified group.

Speeding Up the Recovery

The extra tube didn't just stop the fluid; it helped the patients get back to their lives faster. The Modified group had their main drainage tubes removed sooner (about 6.7 days on average) compared to the Standard group (about 7.1 days). More importantly, they healed faster. Their wounds closed up in about 11.1 days, while the Standard group took about 11.9 days. This small difference meant the Modified group could go home from the hospital sooner (about 6.9 days vs. 8.6 days) and get back to work earlier (about 9.7 days vs. 11.1 days).

Crucially, adding that tiny extra tube didn't make the surgery harder or longer. The time the surgeons spent in the operating room and the amount of blood lost were almost exactly the same for both groups. It was like adding a secret shortcut that didn't require building a new road.

The Long-Term View: Keeping the Cyst Away

The most exciting part might be the long-term results. The researchers followed the patients for one year to see if the cyst came back. In the Standard group, 5 patients (18.03%) had the cyst return. In the Modified group? Zero. Nobody in the Modified group had a recurrence. The study suggests that by keeping the area dry and free of fluid, the new method helps the skin heal perfectly, leaving no room for the cyst to sneak back in.

Why It Works and Who It Helps

The study also dug into why some people were more likely to get that fluid buildup. They found two main culprits: having a large lesion (longer than 7 cm) and not having that extra scalp needle drainage. If a patient had a lesion longer than 7 cm and didn't get the extra tube, their risk of getting a seroma was huge—about 17 times higher than if they did get the tube. This suggests that for patients with bigger cysts, this double-drainage method is especially important.

The Bottom Line

This paper suggests that adding a simple, tiny scalp needle tube to the standard surgery is a safe and effective way to fix a common problem. It doesn't make the surgery scarier or longer, but it significantly reduces the risk of fluid getting trapped, helps wounds heal faster, and might even stop the cyst from coming back. While the study was done at one hospital and looked back at past data, the results point to a simple tweak that could make a big difference for patients dealing with this painful condition. It's a reminder that sometimes, the best solution isn't a giant new invention, but just a little extra attention to the details.

Technical Summary: Modified Karydakis Flap with Dual-Channel Drainage for Pilonidal Cysts

Problem Statement
Pilonidal cysts are chronic inflammatory conditions of the sacrococcygeal natal cleft characterized by sinus tracts, hair retention, and recurrent infections. While the Karydakis flap procedure is a widely accepted, minimally invasive standard for radical resection and primary closure, it faces a significant clinical bottleneck: a high rate of postoperative complications, particularly seroma formation. The anatomical structure of the natal cleft, combined with extensive subcutaneous resection, creates irregular dead spaces prone to fluid accumulation. Standard management relies on a single subcutaneous silicone drainage tube, which often fails to adequately drain these irregular cavities, especially after the main tube is removed. This residual fluid accumulation leads to seroma, which subsequently increases the risks of wound infection, dehiscence, flap necrosis, delayed healing, and disease recurrence. Current literature lacks a simple, minimally invasive drainage optimization that ensures continuous, full-cycle coverage of the dead space.

Methodology
This study employed a single-center retrospective cohort design involving 122 patients treated at the Affiliated Hospital of Qingdao University between December 2022 and December 2024. Patients were divided into two balanced groups (61 cases each):

Standard Group: Underwent the conventional Karydakis flap procedure with a single 8 mm subcutaneous silicone drainage tube for negative pressure drainage.
Modified Group: Underwent the same Karydakis flap procedure but with an added dual-channel drainage system. This included the standard silicone tube plus an auxiliary scalp needle drainage tube (a 7-gauge needle tube with the needle removed, retaining a 10 cm soft tube). This auxiliary tube was inserted via a subcutaneous tunnel at the midpoint of the natal cleft (the lowest point) to provide gravity drainage and address blind spots in the dead space.

The surgical resection, flap advancement, and suture techniques were identical between groups; the only variable was the drainage method. Outcomes measured included seroma incidence, total wound complications, recovery metrics (drainage tube duration, healing time, hospital stay, return-to-work), and 1-year recurrence rates. Multivariate logistic regression was used to identify independent risk factors for seroma.

Key Contributions
The primary technical contribution of this work is the innovative introduction of a dual-channel drainage system for the Karydakis flap procedure. By integrating a simple, low-cost scalp needle tube at the natal cleft alongside the standard negative pressure tube, the study addresses the specific limitation of single-tube drainage in covering irregular dead spaces and managing residual fluid post-tube removal. This approach offers a practical, minimally invasive modification that does not increase surgical trauma or operative time but significantly enhances fluid management throughout the perioperative period.

Results
The study yielded statistically significant improvements in the modified group compared to the standard group:

Complication Reduction: The incidence of seroma dropped significantly from 18.03% in the standard group to 3.28% in the modified group ( $P=0.009$ ). Consequently, the total wound complication rate decreased from 27.87% to 11.48% ( $P<0.05$ ), with wound dehiscence specifically reduced from 16.39% to 4.92%.
Recovery Acceleration: The modified group demonstrated faster recovery across all metrics:
- Drainage tube removal time: Shorter by ~0.37 days ( $P=0.008$ ).
- Wound healing time: Reduced from 11.90 to 11.11 days ( $P=0.001$ ).
- Hospital stay: Reduced from 8.59 to 6.90 days ( $P<0.001$ ).
- Return-to-work time: Reduced from 11.11 to 9.72 days ( $P=0.002$ ).
Recurrence Rates: At the 1-year follow-up, the modified group achieved a 0% recurrence rate, compared to 18.03% in the standard group ( $P=0.023$ ).
Surgical Safety: There were no significant differences in operative duration or intraoperative blood loss between the two groups, confirming that the modification did not increase surgical complexity or trauma.
Risk Factor Analysis: Multivariate analysis identified two independent risk factors for seroma: absence of the scalp needle drainage (OR=10.74) and lesion length >7 cm (OR=17.78).

Significance and Claims
The authors claim that the modified Karydakis flap procedure represents a safe, effective, and optimized surgical regimen for pilonidal cysts. By establishing a dual-channel drainage system, the procedure effectively mitigates the primary cause of postoperative failure (seroma) without adding surgical burden. The study positions this modification as a solution that aligns with Enhanced Recovery After Surgery (ERAS) principles by reducing complications, shortening hospital stays, and accelerating return to daily activities.

The authors conclude that this technique is particularly valuable for high-risk patients, specifically those with lesion lengths greater than 7 cm, where the risk of dead space accumulation is highest. They assert that the procedure is easy to perform, has a short learning curve, and is suitable for widespread clinical promotion across hospitals of all levels to improve long-term surgical outcomes and reduce recurrence risks. The study acknowledges limitations inherent to its retrospective, single-center nature and the 1-year follow-up period, calling for future multicenter, prospective trials to validate these findings over ultra-long-term periods.

Technical Summary: Modified Karydakis Flap with Dual-Channel Drainage for Pilonidal Cysts

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