Clinical Application of a Modified Local Transposition Flap Surgery in Repairing Fingertip Defects


 Purpose: A modified local transposition flap surgery was performed for fingertip injuries. Given the shape of the flap turnover resembling a parallelogram, we called it a parallelogram flap. This transposition flap surgery allows a more significant transfer distance with good outcomes.Method: The study collected patients who underwent parallelogram transposition flaps to repair fingertip defects from 2017 to 2020. 32 cases (32 fingers) were included in our study, including 20 males and 12 females, aged 17 to 60 years, with an average age of 36 years. The causes of injury were crush injury in 13 cases, punch injury in 11 cases and sharp cutting injury in 8 cases. There were 6 cases in thumbs, 6 cases in index fingers, 14 cases in middle fingers, 4 cases in ring fingers and 2 cases in little fingers. The area of fingertip defects was 1.2 cm × 2~3 cm × 4 cm, with bone exposure. The interval between the injury and operation was 5.78 h (the mean value was 4.7-8.4 h). All operations were performed by one surgical team, and the average operation time was 31.2 min.Record The length and width of the finger，two-point discrimination（2PD），Total Active Movement (TAM)and the MHQ (Michigan Hand Questionnaire) of the injured fingers to evaluate the therapeutic effect.Results: all our parallelogram flaps had survived postoperatively.，At last follow-up,There was no difference between the length and width of the reconstructed finger and that of the healthy side（P>0.05）. The qualification rate of the static 2PD of the flaps were 84.37% .The qualification rate of the TAM of injured figures were 100% . Evaluation of the MHQ subscale performance showed that the score of the overall hand function is 93.71, activities of daily living is 95.22, work performance is 94.23,pain score is 4.34 , aesthetics is 92.15 and satisfaction score is 92.45.All of these were perform well.Conclusion: This transposition flap surgery allows a more significant transfer distance with good outcomes.


Introduction
Finger injury is common in our daily life [1]. However, severe injuries may result in skin and soft tissue defects with the exposure of bone, joint, tendon, blood vessels and nerve, leading to dis gurement and impairment of nger function. Several approaches to repairing injured ngers are being practiced [2]. It is generally believed that amputation with sutured closure of the wound may be the most effective treatment, but patients are usually discontented due to the de ciencies of appearance and function [3].
The application of an abdominal ap allows possible rescue of injured ngers [4,5]. However, the abdominal ap belongs to the distal ap and has several shortcomings, such as requiring multi-stage surgeries, poor wear resistance, swollen appearance, poor sense of touch, and requiring hand attachment to another part of the body for up to 3 weeks [6,7]. With the development of ap technology and microsurgery, regional pedicled ap and free ap have become a popular choice in managing injured ngers but again, they are not without drawbacks. While local aps, such as the V-Y aps have the advantages of having similar texture and sensation to the defect area, their applicability is limited when the defect area is large that the wound cannot be covered [8,9]. In this instance, compared with local aps, free aps are superior in facilitating the movement of tissues and restore the aesthetic effect in a single stage [10], but the operation and postoperative care are complex and unfortunately, ap failure is not uncommon. Here, we described a novel transposition ap surgery, which we named the parallelogram transposition ap for ngertip defects and the clinical outcomes were reviewed. With this technique, the length of the ngers was retained while allowing a more signi cant transfer area than the V-Y ap.
Moreover, the aesthetic and function of ngers were preserved.

Patients
Patients undergoing parallelogram transposition aps and V-Y aps to repair ngertip defects from 2017 to 2020 were included in our retrospective analyses. The study was submitted to the Ethics Committee.
Patients deemed suitable for this procedure would satisfy the following inclusion criteria: (1) single ngertip injury of one hand; (2) local soft tissue defects and phalangeal bone exposure without skin ap transplantation; (3) the injured nger had not been longer than 10 hours with light contamination of the wound; (4) the patient agreed to participate at the 4-month follow-up. 64 ngers of 64 cases were treated by parallelogram aps (Group A), and the others (58 ngers of 58 cases) were treated by V-Y aps (Group B). All operations were performed by two surgical teams which had many years of clinical experience.

Wound treatment
All operations were performed by one surgical team. Firstly, the patient was given nerve block anesthesia at the root of the injured nger. A gauze was then placed at the root of the nger and tightened with a rubber band to minimize bleeding. Thorough debridement and hemostasis were performed to the wounded nger. With a partial defect of the phalange, the remnant of the phalange was repaired and the bone structure was polished. The exposed nerve stump was incised with a sharp knife so that the severed end would retract naturally into the normal soft tissue.

Harvesting of skin ap
Group A According to the size of the defect, the ap was designed on the side with more residual skin (Fig. 1). A longitudinal incision was made along the bone surface on both sides of the ngertip and the incised position should not exceed the transverse striation of the distal interphalangeal joint. Then, the skin and subcutaneous tissue were incised along the edge of the skin, and the skin ap was dissected sharply within the subcutaneous fascia, avoiding injury to the proper digital artery and nerve. A transverse incision was made on the side with more remaining skin to provide su cient angle for ap turnover. Once freed, the designed ap was ipped over. Given its shape resembling a parallelogram, we named the ap a parallelogram ap. The longest hypotenuse c should be longer than the longitudinal length a + the width of defect b (Fig. 2), which was su cient to cover the defective area. After the ap was ipped over, a piece of skin graft A was left on the opposite side. The constructed skin graft A could be used to repair the transferred skin defect B. (Fig. 6, 7) Group B The distal edge of the wound is the base of the ap; the ap's apex should extend to the distal interphalangeal crease (Fig. 3). The skin and subcutaneous tissue are then incised, including the brous septa anchoring the pulp tissue to the bone. Damage to the neurovascular bundles should be avoided.
The ap can be advanced up to 1 cm over the defect and secured with sutures, creating a Y-shaped repair (Fig. 5).

Postoperative management
Postoperatively, antibiotics were given intravenously to reduce the risk of infection, in addition to lamp baking heat preservation and other symptomatic treatment. Moreover, patients received regular dressing changes and were advised to bed rest, elevate the affected limb, stop smoking, keep warm, and regularly observe the perfusion of the skin ap.

Follow-up
2.4.1 The Total Active Movement (TAM) of the injured ngers was measured using a standard hand goniometer. The system sums the degrees of active exion at the interphalangeal joints and metacarpophalangeal joint and subtracts the degrees of the extension de cits (100% for excellent; > 75% for good; > 50% for fair; < 50% for poor) 2.4.2 The sensibility of the palmar part of the aps was measured using static two-point discrimination (2PD). The mod ed American Society for Surgery of the Hand guidelines were used to classify the 2PD (< 6 mm for excellent; 6-10 mm for good; 11-15 mm for fair; > 15 mm for poor). 2.4.3 The MHQ (Michigan Hand Questionnaire) was used to subjectively evaluate outcomes of the repaired hands. The MHQ includes 6 subscales (overall hand function, activities of daily living, pain, work performance, aesthetics, and satisfaction).

Results
The characteristics of the study samples are detailed in Table 1. All the aps and the skin grafts survived completely in the two groups. Patients in two groups did not differ with respect to age, gender, the cause of injury, the nger type, the interval between injury and surgery and the duration of surgery (P > 0.05 for each). There was no difference with operative duration and follow-up time in two groups (P > 0.05 for both) (Table 1). Accordingly, the patients' baseline assessment indicated that the two groups were functionally similar, and the selection bias appears to have been limited. At last follow-up, the frequency distributions of the static 2PD of the aps in the two groups were presented in (Fig. 4), and there was no difference with the 2PD of the palmar part of the aps (Table 2) and the TAM of injured gures in Group A and Group B ( Table 3). The MHQ summary scores in Group A were much higher than in Group B (P < 0.01). Evaluation of the MHQ subscale performance showed that the overall hand function, activities of daily living, work performance and pain score had no differences, but aesthetics and satisfaction score was higher in Group A (P < 0.01 and P < 0.05, respectively) ( Table  4).

Discussion
Fingertip injury represents the most common injury of the hand [11], which is de ned as a distal injury of the exor digital tendon and extensor tendon insertion [12]. In the management of a ngertip injury, although it is essential to maintain the length, preserve the nail and the appearance, the main goal of treatment is to ensure the durability of the ngertip and painless at the skin. Therefore, the treatment must be individualized based on several patient-related factors and unique trauma characteristics [13].
For those injured ngers with bone exposure and local soft tissue defects, stump revision (i.e., phalangeal shortening and direct suture) is the simplest and fastest way to recovery, which can be performed under local anesthesia in the emergency room [2]. However, this operation shortens the phalange and adversely affects the appearance and function of the affected nger. With the advancement of medical technology, stump revision is no longer a common approach to manage tissue defects [3]. Compared with stump revision,, given that our method demonstrated a similar length of operative time and di culty while retaining the length and function of the affected nger.
At present, the "V-Y" advancement ap [14] is widely performed in the management of ngertip injuries.
"V-Y" ap is best used for transverse or anticlinal ngertip amputation and is suitable for injury to any nger. The contraindications of applying this ap include oblique metacarpal ngertip amputation and extensive palmar soft tissue defects. The edge of the wound is at the bottom of a distal triangle of the ap, and the apex of the ap can be extended to the transverse striation of the distal interphalangeal joint. During the operation, the skin and subcutaneous tissues should be incised rst, including the ber septum, and injury to the neurovascular bundle should be avoided. The ap can be advanced 1 cm to the distal end and form a "Y" shape repair. With this method, the maximum advancement distance of the skin ap is limited to 3-4 mm [15] and the skin ap area provided are often inadequate. Moreover, the incision of this operation is made at the nger pulp and the postoperative scar is located at the middle of the nger pulp, which may affect the sensory function. On the other hand, the most widely used transfer ap, the "V-Y" ap is widely used, but its shortcomings still need to be further improved. The parallelogram transfer method allows a longer transfer distance of the transposition ap. In our practice, the residual skin was trimmed and ipped over. The transverse width of the ap was abandoned and the longitudinal length of the ap was obtained. The defects were evenly distributed on each side of the parallelogram to achieve su cient transfer distance to cover the exposed bone and tissues.
This article provided a detailed description of a modi ed ap for the surgical management of ngertip defects. The transfer ap was incised closely to the bone surface of the distal phalanx, and the interphalangeal artery was not damaged during stripping [16,17], which is key to ap survival. Venous out ow is maintained by venules and capillaries in the perivascular adipose tissues through a retrograde fashion [18]. Therefore, if the interphalangeal artery is well protected during the ap design, the ap survival can be assured more con dently, as evidenced in our analyses that all our parallelogram aps had survived postoperatively.
The reconstructive surgery for ngertip injury aims to obtain stable tissue coverage, achieve acceptable appearance, restore sensitivity, maintain nger length and resume normal physical activity promptly [19]. After a careful preoperative design of the parallelogram ap, postoperative skin ap contracture is less likely to occur, given that the turning over of the ap provides more coverage area than the "V-Y" ap.
Furthermore, the incision of the parallelogram ap is distributed at both sides of the ngertip, and therefore the scar is at the sides of the nger. In this way, we abandon the nger's width and retain the length, successfully achieving the purpose of the operation. The practice of sensory or non-sensory reconstruction of ngers remains controversial and debatable among hand surgeons. Studies have reported an average of 10 mm in the static two-point discrimination test when a "senseless" reverse digital artery island ap has been performed [20,21]. Conversely, other studies have demonstrated a normal static two-point discrimination test (1-5mm) following neurovascular island aps [22,23]. The ndings of these studies indicate a reduced ability of aps to restore sensation in the absence of nerve connections [24][25][26]. By performing free ap surgery, the digital nerve can usually be preserved. We demonstrated that our operative method provided a good sensory reconstruction of ngers, leading to satisfactory recovery in the nger movement, strength, etc.
There were limitations to our parallelogram ap. In particular, this ap would not be applicable when there were multiple skin defects at the donor site, or the required transfer distance was more than 6-7mm. In this instance, the skin ap adjacent to the nger or a reverse-ow island ap can be considered.

Conclusion
The reconstruction using parallelogram aps is a easier and more versatile treatment with better functions, less morbidity and better aesthetics. This method is a better choice for reconstruction of ngertip injury.

Declarations
Ethics approval and consent to participate Retrospective clinical study was approved by Jinshan Hospital of Fudan University's institutional review board (JIEC 2021-S21-01). This study was conducted in accordance with the Declaration of Helsinki. All the patients consented to participate in this study, and informed consents were signed by themselves in all instances. In addition, the parents or guardians of the study participants gave written consent for their respective minors to participate in the study.

Consent for publication
Written informed consent was obtained from the patients' guardians for publication of clinical data.

Availability of data and materials
The datasets of the current study are available from the corresponding author upon reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This study was funded by Jinshan Hospital of Fudan University(No.JYQN-LC-202107)