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Flow-through arterialized venous free thenar flaps for palmar soft tissue defects in fingers

Objective To evaluate the efficacy of venous free thenar flaps for reconstructing palmar soft tissue defects in fingers. Methods From December 2018 to October 2019, 11 patients with palmar soft tissue defects in fingers were treated using venous free thenar flaps. At the final follow-up, the range of thumb radial and palmar abduction on the injured side and opposite side was calculated. The total active movement (TAM) of the injured and opposite fingers and flap sensibility recovery were also recorded. Results The mean follow-up time was 13.4 months, all flaps survived, and all wounds at the donor sites healed with no skin necrosis. At the last follow-up, the average range of thumb radial abduction and thumb palmar abduction on the injured side was 96.6% and 95.9% of the value on the opposite side, respectively. The average TAM of the injured fingers was 98.2% of the value of the opposite fingers. Sensation in the flaps was restored to grade S2 to S3. Conclusion Venous free thenar flaps can be alternatives for reconstructing palmar soft tissue defects in fingers.

Palmar soft tissue defects in fingers are very common in hand injuries. Owing to its unique features, such as a thick epidermal layer and poor mobility, the palmar skin of the finger helps humans achieve various functions, such as holding and grasping. Because of its importance, many methods have been used to repair palmer soft tissue defects to achieve better recovery. [1][2][3] With societal developments, patients have higher requirements regarding their appearance, and sensory and functional recovery after surgeries. 4 Therefore, when flaps are selected to repair soft tissue defects, not only coverage, but also function and aesthetics should be considered. [5][6][7] Compared with the palmar skin of the finger, the thenar skin has a similar texture, which makes it an ideal source for repairing palmar soft tissue defects of the finger. 8 Common thenar flaps used for reconstructing soft tissue defects of the fingers are pedicled thenar flaps 9 and free thenar flaps with arteries. 10 However, these flaps have inevitable shortcomings; pedicled thenar flaps may require second-stage operations, and creating free arterial flaps may lead to more damage to the healthy tissues.
Venous flaps have been applied clinically for some time. 11 The veins in the thenar region are superficial and widely distributed, which makes them easy to observe and harvest. Therefore, considering the skin texture and anatomical features, we made good use of the superficial veins and improved the traditional free thenar flap for reconstructing soft tissue defects in fingers. The purpose of this study was to evaluate the use of venous free thenar flaps for repairing palmar wounds in fingers.

Materials and methods
From December 2018 to October 2019, 11 patients with palmar soft tissue defects of the hands were treated with venous free thenar flaps. The inclusion criteria were (1) acute or chronic palmar soft tissue defect(s) of the finger; (2) defects no larger than 4.0 cm in length and 2.5 cm in width; and (3) no obvious infection. Exclusion criteria were (1) defects larger than 4.0 cm long or larger than 2.5 cm wide; (2) bone or tendon injury that could affect the accuracy of postoperative joint range of motion; (3) injury to the thenar area of the hand; and (4) concurrent diabetes or vascular disease that could affect flap survival. Table 1 lists the demographic data of the 11 patients. This study was approved by the institutional review board of Shanghai General Hospital, and each patient provided signed informed consent before participating in the study.

Surgical technique
All patients were placed in the supine position under general anesthesia. A tourniquet was placed at the upper third of the upper arm on the injured side, with a pressure of 250 mmHg. After thorough debridement (Figure 1a), the wound area was measured, and satisfactory arteries and veins were detected using an operating microscope, for future use. The radial base of the proximal phalanx of the thumb and the scaphoid tubercle were palpated and marked. These two points were then connected with a line, and the midpoint was marked. With this midpoint as the center and the line as the longitudinal axis, the flap was designed to be slightly larger than the wound (Figure 1b). The skin along the edge of the flap was incised, and the number and positions of veins at the flap edge were observed and marked. The veins were carefully detected along the opposite direction of the flap for approximately 5 mm and then cut (Figure 2a). The flap was then harvested along the surface of the thenar muscles. The entire process was performed using an operating microscope. The donor site was sutured directly with 3-0 coated Vicryl Plus antibacterial suture (Ethicon Inc., Somerville, NJ, USA). After the flap was transferred to the wound, one artery in the recipient site was anastomosed to one vein in the flap using 10-0 Prolene (Ethicon Inc.). Then, one vein in the recipient site was anastomosed to one vein in the flap (Figure 2b). Each vascular anastomosis was performed using an operating microscope.

Postoperative management
The color, capillary refill, and temperature of the flaps were evaluated daily. If venous crisis occurred, heparin was wiped along the flap edge until the effusion turned to fresh blood. Dressings were kept loose to avoid compressing the flaps and obstructing blood flow. After the wounds had healed, the patients began rehabilitation and exercises under the guidance of a physiotherapist.

Outcome evaluation
In this study, each patient's gender, age, cause of injury, defect size, flap size, and follow-up time were recorded. Postoperative complications, such as skin necrosis at the donor sites and flap necrosis at the recipient sites were recorded. We evaluated the scar at the donor site according to the Vancouver scar scale (VSS). The range of thumb radial and palmar abduction of the injured side and opposite side was calculated, as well as total active movement (TAM) (metacarpophalangeal plus interphalangeal) of the injured finger and opposite finger. According to the British Medical Research Council's sensibility recovery grading standard, the sensibility recovery was described as S4, S3þ, S3, S2, S1, or S0, from excellent to poor. Another group of hand surgeons who did not participate in the surgeries performed these assessments.

Results
The mean follow-up time was 13.4 months (range: 10-20 months); all flaps survived (Figure 3a), and all wounds at the donor sites healed with no skin necrosis. Five flaps (45.5%) in the 11 cases had some degree of swelling, which resolved after symptomatic treatment within 2 to 3 days after the operations. At the last follow-up, the average VSS score at the donor sites was 4.5 (range: 4-6). The average range of thumb radial abduction and thumb palmar abduction of the injured sides was 96.6% and 95.9% of the value of the opposite sides, respectively ( Table 2). The average TAM of the injured fingers was 98.2% of the value for the opposite fingers, and the sensibility recovery of the flaps was restored to grade S2 to S3 (Table 3).

Discussion
Thenar flaps were first used for soft tissue defects of the hands by Flatt 12 in 1957. Subsequently, Neuman 13 and Kamei 14 made further improvements, and the application of thenar flaps was gradually popularized. Pedicled thenar flaps are relatively easy to harvest to repair soft tissue defects of the finger, but a second-stage surgery is usually necessary to remove the pedicle. Furthermore, prolonged flexion of the fingers can cause intense discomfort to patients. When harvesting free thenar flaps, including the superficial branch of the radial artery, more damage may be caused to the surrounding healthy tissues. The propeller perforator flap is also often used to repair soft tissue defects; however, its disadvantage for palmar soft tissue defects in the fingers is that skin grafting is often required at the donor site. 15 Since the successful animal experiments involving flaps nourished by arterial inflow through the venous system that were performed by Nakayama 16 in 1981, greater numbers of venous flaps [17][18][19][20][21] have been reported for repairing soft tissue defects, although the mechanism of flap survival remains unclear, and complications may occur, such as pigmentation. 22 In our study, all flaps survived without the common disadvantages of conventional venous flaps, such as swelling and pigmentation, and the flap survival progression was similar to that of arterial flaps. It is important to remain close to the surface of the thenar muscles when harvesting thenar flaps to protect the thenar muscles and ensure that their function remains unaffected. The ranges of thumb radial abduction of the injured side and the opposite side were nearly the same in our study, as were the ranges of thumb palmar abduction. We encountered no skin necrosis at any donor sites, and the donor site wounds healed completely with only linear scars. The average VSS score was 4.5, and no patients reported  discomfort. The intact thenar muscles played a role in natural skin dilation and ensured satisfactory fullness of the thenar area. None of the flaps developed edema, and all fingers had smooth appearances. Compared with the opposite finger, the joint function of the injured finger was almost completely restored in all cases. In all 11 cases, we performed precise vascular anastomosis of two vessels, namely one artery and one vein. Although all of the flaps survived, we found that the survival progression of the flaps differed. Five flaps (45.5%) in the 11 cases had some degree of swelling that resolved after symptomatic treatment within 2 to 3 days after the operations; the other flaps did not develop swelling and healed successfully. In the postoperative observation, we found that more vascular crises in the flaps occurred in the veins rather than in the arteries. Even though the diameter of the peripheral vessels is very small, as long as we ensure the anastomosis quality, the blood supply can meet the needs of flap survival because of the small area of the flap. However, the possibility of flap necrosis caused by venous crisis requires more attention. It is worth mentioning that thenar flaps can be used to reconstruct the lost fingerprint (Figure 3b) owing to the original injury and improve the quality of life of patients with soft tissue defects in the pulp, which is required in modern society.
The maximum width of the flaps in our study was 2.5 cm, and further study is needed to explore whether wider donor site flaps can heal successfully after direct suturing. When performing vascular anastomosis, the arteries in the wound at the recipient area should be fully utilized. If available arteries matching the diameter of the veins in the flap can be found, it is not necessary to make another skin incision to search for available arteries, which causes additional damage to the healthy arteries and skin.
The recovery of sensibility is an important index to evaluate the flap, 23 especially for repairing palmar soft tissue defects of the finger. In our study, sensibility in four cases reached grade S3, and sensibility in the other seven cases reached grade S2 according to the British Medical Research Council's sensibility recovery grading standard, at the last follow-up. To test whether sensibility recovery can be further improved, in a future study, we will conduct long-term follow-up of sensibility recovery of the flaps, using the Semmes-Weinstein monofilament (SWM) and static two-point discrimination (2-PD) evaluations. Although the assessment of sensibility recovery requires long-term follow-up, we believe that venous free thenar flaps have great potential in the reconstruction of palmar soft tissue defects in fingers.
Venous free thenar flaps are reliable owing to the constancy of the veins and ease of dissection. Dissecting these flaps causes little damage to the healthy tissues, which ensures that postoperative hand function is satisfactory, the color and texture of the flap is close to that of the palmar skin of the finger, and good aesthetic appearance can be achieved. The disadvantages of the method are the need for skilled microscopic technique during the operation and strict observation and nursing after the operation because postoperative swelling and congestion might occur.

Declaration of conflicting interest
The authors declare that there is no conflict of interest.

Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.