Digital mucoid cysts are frequently found at the distal interphalangeal (DIP) joint in patients with degenerative osteoarthritis [1-3]. These cysts were first reported in 1883 as synovial lesions of the skin [3]. Since then, mucoid cysts have been named by multiple nomenclatures such as synovial cysts, myxoid cysts, and ganglions due to their unknown pathophysiology and cause [2,3]. Prevention of mucoid cysts was important; however, when mucoid cysts are large, severe, or painful, or they are disrupted and accompanied by skin ulceration, surgical treatment is required. In particular, skin ulceration with a disrupted mucoid cyst or thinned skin due to a long-standing cyst needs to resect the entire skin envelope and perform flap coverage. Even though appropriate flap coverage was performed, the recurrence of mucoid cyst occurred by incomplete excision of the cyst stalk and progression of degenerative arthritic changes. Therefore, appropriate operative and perioperative management was essential for the resolution of mucoid cysts [1,3,4].

Multiple local flap choices can be used for the defects above the DIP joint, including a dorsal Hueston flap, a dorsal advancement flap, and a rotation flap [3,5]. Bilobed flaps were first proposed by Esser in 1918 and were first used in 1953 for nasal labial reconstruction [1]. Their first application to defects of digital soft tissue was by Young and Campbell [2]. Bilobed flaps are now considered a reliable choice for digital soft tissue defects, with primary healing of the donor site [2]. In this article, we describe our retrospective evaluation of surgical outcomes following bilobed flap after digital mucoid cyst resection.

Between July 2022 and February 2024, 26 bilobed flap surgeries for DIP joint soft tissue defect after mucoid cyst excision were performed at our institute and included in this study. At each patient’s first visit to our clinic, we recorded their demographic data (sex, age, time to surgery), and clinical findings (including cyst size and location, the presence of nail ridging, and signs of infection) were recorded. A plain X-ray was conducted to determine whether osteophytes had developed and identify any arthritic changes in the DIP joint. The diagnosis was made based on the combined clinical and radiographic findings. Surgical treatment was considered when the cyst is painful, aesthetically problematic, disruptive and ulcerous, or recurrent. Postoperative follow-up is routinely and regularly conducted at our institute. At each outpatient clinic follow-up, we assess wound status, wound healing time, and other complications.

Table 1 shows the patient demographics and follow-up data. There were 19 female and seven male patients in our cohort. The average age was 62.2 years (range, 45–78 years). This roughly corresponds to the demographics reported in previous studies [1,4,7-9]. Eight mucoid cysts were located at the interphalangeal joint of the thumb, 10 were located at the DIP joint of the middle finger, six were located at the DIP joint of the ring finger, and two were located at the DIP joint of the little finger. The average time to surgery was 10.8 months (range, 1–60 months). The average cyst size was 6.9×8.3 mm (range, 0.4–1.0×0.5–1.3 mm). On their preoperative X-ray, 22 patients (84.6%) had a definite osteophyte of the DIP joint. Nail ridging was found in 19 patients (73.1%). It occurred only when the cyst was located at the nail fold; if it was located on the radial or ulnar side of the DIP joint (away from the nail root), there was no nail ridging.

All of the flaps survived without major complications. In one patient, there was delayed wound healing due to partial flap necrosis. In this patient, the bilobed flap for mucoid cyst resection and DIP joint arthrodesis for severe degenerative osteoarthritis were performed. It may have been caused by flap damage during the ostectomy of the distal phalanx base and middle phalanx head using oscillating saw. During the follow-up period in our cohort, there were no recurrences of the cyst.

Digital mucoid cysts are benign ganglionic or synovial lesions of the interphalangeal joint [5,6]. Treatment methods include aspiration of the cyst or surgical excision [1,2,4]. Although the recurrence rate following aspiration is approximately 60%, nonsurgical treatment is preferable if the cyst is asymptomatic [1]. However, if the cyst was symptomatic or recurrent, surgical treatment was considered [4]. Standardized indications for surgical treatment have not yet been fully established, but Rizzo and Beckenbaugh [1] have suggested that the failure of previous nonsurgical treatment or the presence of nail ridging was considered a surgical indication. Nail ridging indicated a more mature cyst with an established stalk [4,6]. The indications for surgical treatment used in our institute are somewhat broader and include painful cysts, aesthetic issues, and recurrence despite conservative management such as aspiration or steroid injection.

The most frequently affected fingers in our patients were the thumb and middle finger, which differed from previous reports, in which the index finger was the most affected. In addition, nail ridging was seen in about 73% (n=19), which was a higher rate than has previously been reported. This is likely because our sample included only patients who received surgery [8-10]. The average time to surgery was 10.8 months. Almost all patients do not seek treatment for mucoid cysts for a long time or continue the repetitive conservative treatment for a long time before they visit our clinic. DIP joint osteophytes were seen in the preoperative X-rays of 84.6% (n=22) of our patients. Rizzo and Beckenbaugh [1] reported a slightly higher rate of 91%. Although the pathophysiology of mucoid cysts was not fully established, the mucinous formation was related to degenerative changes in previous studies [1-3]. Our authors also agreed that DIP joint mucinous formation was related to arthritic changes with osteophyte resection or severe synovitis in the DIP joint. Therefore, we performed osteophyte resection if possible or joint debridement in all cases because mucoid cysts are known to be related to degenerative changes in the DIP joint, it was related to the presence of the osteophyte or DIP joint synovitis [4].

During the follow-up period, we monitored patients for postoperative complications, including recurrence of the mucoid cyst, joint stiffness, infection, and delayed wound healing. We defined joint stiffness defined as a decrease in the range of motion of the affected joint greater than 50%. Stiffness occurred in 11% of our patients, while Rizzo and Beckenbaugh [1] reported a postoperative stiffness rate of 8%. Postoperative stiffness may be related to surgical scarring and arthritic changes after osteophyte resection and bilobed flap. With the bilobed flap coverage after mucoid cyst resection, a scar crossing the DIP joint occurred inevitably in almost all patients. As our surgical technique, the point that the second lobe design should not be positioned in a vertical direction with DIP and PIP joint and tension-free and redundant flap coverage with bilobed flap can minimize postoperative stiffness. In addition, patients with DIP joint stiffness in our series did not complain about the limitations in range of motion; they used their digits without any discomfort during daily life.

A previous report found a recurrence rate after cyst excision and osteophyte resection of 0% to 3.5% [4]; there was no recurrence in our patients. Delayed wound healing and infection occurred in 3.8% (n=1) of our cases, which was a lower rate than seen in previous reports [1,4].

After the introduction of first bilobed flap by Esser in 1918, Zimany [10] proposed a modified (self-closing shape) design in 1953. In 1989, Zitelli proposed a further modification, known as the geometric bilobed design, which design used in this study (Fig. 1) [4]. Zitelli’s design was initially proposed for use in nasal surgery, for which the angle between the defect axis and the second lobe axis is 90° to 100° [4]. However, in the fingers, there is less relaxation of the skin and soft tissue than in the nasal area, so we proposed decreasing this angle to 80° to 90° for the digital mucoid cyst surgeries performed in our cohort studied. Other local flap techniques for mucoid cysts include dorsal Heuston flaps, dorsal advancement flaps, and the rotation flaps developed by Kleinert et al. [11]. The advantages of bilobed flaps for these cysts include more aesthetically pleasing results than can be obtained with the aforementioned flap types, primary healing of the donor site, reproducibility, and easy-to-flap elevation. The bilobed flap can achieve total coverage using soft tissue near the defect, reducing the dissection area, with no need to cross the PIP joint. This modified bilobed flap design for soft tissue coverage of the defect after mucoid cyst excision produces high-quality surgical results.

A large number of patients with osteoarthritis in the DIP joint develop mucoid cysts, and complicated mucoid cysts require surgical resection. Soft tissue coverage with a local flap is required after the excision of a mucoid cyst of the DIP joint. Based on our case series, the modified Zitelli bilobed flap is considered to be a favorable option for coverage of soft tissue defects after mucoid cyst excision, which yields favorable aesthetic and functional outcomes.