A DMC is a common cyst that is defined as a ganglion involving the DIP joints of the fingers or the IP joints of the thumbs [5, 9]. Surgical excision of DIP or IP mucous cysts is necessary when a patient reports discomfort in daily activities, the cyst is causing slight nail deformity, or the surrounding skin becomes fragile and thin, leading to pain and increasing the risk of joint infection . However, many patients have skin defects that are too large to be sutured directly due to high tension at the incision after removal of a DMC, which may result in skin necrosis. Therefore, many kinds of flaps have been designed to overcome this challenge. Jiménez I reported a Zitelli bilobed flap  that can sufficiently cover the skin over the DIP joint in a short period. Skin necrosis occurred in one case on the most distal part of the first lobe after surgery, which healed by secondary intention without the appearance of a synovial fistula at the final follow-up. Johnson SM  reported a local advancement skin flap and did not observe skin necrosis during the follow-up. Imran D  reported a rhomboid flap and observed no skin necrosis. Although these flaps can sufficiently repair skin defects after DMC removal and lead to excellent results, the procedure is challenging in terms of significant donor site morbidity and requires intensive postoperative monitoring, microsurgical skill, appropriate equipment and many operating room resources .
The usefulness of bipedicle advancement flaps to cover skin defects has been established, and the use of such flaps has been widely reported in the literature at various anatomic areas, including the scalp, eyelids, ears, upper forehead, nose, chin, mucosa, lip, neck, trunk and extremities . However, only a few studies have reported using this flap to cover defects after removal of a DMC.
In our research, DMCs were treated with cyst resection, osteophytectomy and a bipedicle advancement flap to cover the defect. All the flaps survived after surgery, and the incisions healed well. No infections occurred, and no cyst recurred during the follow-up. No difference was found between the preoperative and postoperative ROMs of the thumb IP or DIP joints.
Whether removing osteophytes is necessary remains controversial. Although some authors have reported successful treatment of DMCs without osteophytectomy [10, 15], many authors have reported that removing osteophytes is an important step for treating DMCs [9, 15–17], and these studies showed that osteophyte removal resulted in a low cyst recurrence rate. However, some authors have reported that aggressive osteophytectomy caused a decreased ROM of the DIP joint . In our study, osteophyte formation was found in 14 fingers, and all the osteophytes were removed. We ensured that the excision did not involve the edge of the normal articular cartilage when the osteophytes were removed.
Mucous cysts are subcutaneous but may be covered with thin skin with or without ulceration . After resection of the cyst, the bipedicle advancement flap can be used to cover the postoperative skin defect when the incision cannot be sutured directly due to high tension at the incision. When we made the second incision, we used a similar length and arc to the proximal edge of the incisional defect and maintained a distance between the two incisions of at least half the length of the proximal incisional edge. The new incision extended along the extensor tendon surface, and the flap was separated from the tendon surface. These steps were performed to maintain as much blood circulation as possible to the flap.
The use of a bipedicle flap for skin coverage after DMC excision has the following advantages: (1) The flap is safe due to its dual pedicle blood supply, thus decreasing the risk of flap necrosis or flap failure. (2) Bipedicle flaps allow increased tissue movement by direct advancement. The blood supply artery does not need to be dissected, and the flap pedicle does not need to be twisted when covering the defect. (3) Use of this flap often allows scars to be hidden in the skin lines of the dorsal side of the thumb IP or DIP joint. (4) Donor site morbidity and postoperative monitoring requirements are minimal. As the flaps use local tissue, the surgeon has a greater ability to successfully match the skin color and texture. (5) Importantly, once a bipedicled flap fails, other strategies can still be employed to cover the defect .
In conclusion, mucous cyst excision together with the overlying skin, removal of osteophytes on the affected side, and coverage with a bipedicle advancement flap provides reliable treatment results with high patient satisfaction and a low recurrence rate based on our experience. Some points should be kept in mind when using this flap. First, as a random flap, the flap length:width ratio should not exceed 2:1 to enable sufficient blood supply. Second, the flap pedicle and the digital extensor tendon should be protected carefully.Third, the excision did not involve the edge of the normal articular cartilage when the osteophytes were removed.Furthermore, the long diameter of the transverse spindle-shaped incision should be parallel to the skin of dorsal side of the thumb IP or DIP joint, allowing the surgery scar to be easily hidden.