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The Free Flap Based on a Single Proximal Perforator of Radial Artery: the Ultrasonography Study and Clinical Applications in Reconstruction of Digital Defect

Background: To locate the anastomosable constant perforator of radial artery on the proximal forarm using ultrasonography, and describe the application of free radial artery flap based on a single proximal perforator in the reconstruction of digital soft tissue defects. Methods: In 20 forarms (10 right and 10 left) from 10 volunteers, the perforators in the proximal half of forarm from radial artery were visualized by ultrasonography. Then the free radial artery perforator flaps based on the single perforator were used for reconstruction of small digital soft tissue defects in 4 cases between October 2017 and May 2018. Results: Of the 20 forarms, anastomosable perforator was constantly detected from the radial artery in the proximal half of forarm. The diameter of the perforator was 0.7±0.1 mm, the pedicle length is 12±3 mm by ultrasonography. Ther location of the perforator is far from elbow crease 8.8±1.4 cm, and the relative distance of the perforator location from elbow crease to wrist crease is 37.2% ± 4.8%. In clinical cases, all the flaps were complete survival. Flap size ranged from 3.5 to 6.5 cm in length and 2.3 to 3.0 cm in width. Donor sites of forearm were closed primarily in all cases. During a mean period of 12 months (8-14 months) follow-up, there were satisfactory results of digital function and cosmesis,and no functional impairments at the donor sites. Conclusions: There is an anastomosable perforator consistent located on the radial artery in the proximal half of forarm. The free radial artery small flap based on this single perforator provides acceptable functional and cosmetic outcomes for the reconsturction of digital soft tissue defects . the the main vessel (radial option for handsurgery reconstruct ultrasonography. These ultrasonography data illustrate the perforator is consistently located at the radial artery in the proximal half of forarm, and designing a free flap based on this single perforator could be achieved. Furthermore, the diameter of the perforator can match with digit artery well in the reconstruction of finger. The multiple superficial veins in forarm can be harvested as an alternative donor vein for venous drainage. Our study is also

Since the radial forearm flap has been first descripted by Yang in 1978 [10] , the anatomy of perforators of radial artery in forearm have been studied systematically [11][12] , and this perforator cluster pedicle flap has been widely used in head or neck reconstruction as a free transer, [13] and hand or elbow soft defects reconstruction as a reginal transer. [14][15] Howerer, either free or pedicle radial forearm flap which is havested as traditional surgical technique has the main limitations is that the flap must sacrifice a major axial artery for upper extremity. In 2004 and 2005,in order to preserve of the radial artery, Lin and Omer firstly attempted to havest proximal perforator clusters flap from radial artery of forearm to reconstruct head and hand defects,respectively. [16][17] Duplex ultrasonography is a well-known method of identifing and evaluating the perforators for free flap transfer. The aim of this study is to locate a constant anastomosable perforator of radial artery on the proximal forarm using ultrasonography, and then raise a free flap based on this single perforator in clinical cases to assess the flap's potential application for reconstruction of the digital soft tissue defect.

Ultrasonography Study
In 20 forarms (10 right and 10 left) from 10 healthy volunteers (5 women and 5 men) with a mean age of 32 years old (range from 23 to 49 years old), the perforators arising from the radial artery were identified in the proximal half of forarm by Dopple ultrasonography (Siemens, Acuson s2000; siemens medical solutions USA, inc; CA, USA). All of the 10 volunteers were right handed and had no medical history of upper limb trauma, surgery, peripheral vascular disorders, or systemic metabolic diseases. When the radial artery and its perforator were identified and located with a 14L5 highfrequency probe (5-14MHz) under the position of forearm completely supinated, the perforator internal diameter and the pedicle length from radial artery to deep fascia were measured and recorded. (Fig. 1) The distance from the perforator location to the elbow crease (D p ) and the distance from the elbow crease to the wrist crease (D E-W ) were measured, then relative distance of the perforator location on the ratio from the elbow crease to the wrist crease was calculated (D p / D E-W ×100%). (Fig. 2) All the data were recorded as mean±standard deviation.

Patients
Between Oct 2017 and May 2018, 4 patients (1 men and 3 women) underwent reconstruction of digital soft tissue defects using the free radial artery perforator flaps based on the single perforator under the China-Japan Union Hospital of Jilin University ethics committee-approved protocol. The ages of the patients ranged from 21 to 47 years. 3 of 4 patients had double or multiple digital defects, the free radial artery perforator flap was used to reconstruct one digital soft tissue defect, other digital soft tissue defects were reconstructed by orther free flaps (such as superficial palmar branch of radial artery free flap or dorsal interosseous artery free flap).

Surgical Technique
Before the operation, the location of the perforator arising from the radial artery was determined and

Postoperative Management and Follow-up
Standard postoperative free flap care and monitoring was performed for 7 days. Routine wound cleansing was accomplished using iodophor postoperation. Low molecular weight heparin (5000 IU per day) and lower molecular weight dextran (500 mL per day) were continuous used to prevent thrombosis of the microsurgical anastomoses. All the patients were instructed to avoid strenuous exercise for 3 weeks. All skin sutures were removed at 2 weeks after the operation.
During a period of 12 months follow up, the flap and the donor site morbidity were estimated by a patient questionnaire and grading following five categories: 5, very satisfied; 4, somewhat satisfied; 3,neither satisfied nor dissatisfied; 2, somewhat dissatisfied; 1,very dissatisfie . [18] Results

Ultrasonography Result
The anastomosable perforator is constantly detected from the radial artery in the proximal half of 20 forarms from 10 healthy volunteers by ultrasonography. The internal diameter of the perforator is 0.7 ± 0.1 mm; the pedicle length from radial artery to deep fascia is 12 ± 3 mm; the distance from the perforator location to the elbow crease (D p ) is 8.8 ± 1.4 cm, and the relative distance of the perforator location beyongd the elbow crease (D p / D E-W ×100%) is 37.2% ± 4.8% ( Elbow crease is 0%; wrist crease is 100%).

Discussion
Various trauma often leaves the hand surgeon with a complex defect in the hand, and the small defect (especially multiple digital defects) is always challenging for reconstruction. The ideal reconstruction of digital defects is the preservation function of hand as much as possible, meanwhile, providing an aesthetic appearance both in recipient and donor region. So among the various options for reconstruction of small soft tissue defects in the fingers, the free flaps have been recognized as the best reconstructive option. [1][2][3] The radial forearm flap has been first descripted by Yang in 1978, [10] and this pedicle flap has been established its role in plastic reconstructive field by surgeons. [13][14][15] Howerer, either free or pedicle radial forearm flap remains the main disadvantage is that the sacrifice of a major artery to the upper extremity. Generally, sacrifice of the radial artery doesn't cause an ischemic problem unless the ulnar artery has been previously injuried in the upper extremity. However, several studies have reported serious complication (eg. hypothenar hammer syndrome; dry gangrene of fingers) after harvesting a radial forearm flap. [19][20] Based on the the anatomical study of proximal perforators of radial artery in forearm, [11][12] Lin and Omer attempted preliminarily to havest this perforator free flap in order to preserve of the radial artery in clinic, [16][17] and then there are few literature to describe and use the proximal perforator from radial artery of forearm for free tansfer. We design this study is to locate a constant anastomosable perforator of radial artery on the proximal forarm using ultrasonography, and then raise a free flap based on this single perforator in clinical cases to assess the flap's potential application for reconstruction of the digital soft tissue defect.
Several previous studies about the perforators analysis of radial artery have confirmed that two main clusters perforators (≥ 0.5 mm diameter; distal cluster and proximal cluster) in forarm could be potentionally used for flap transfer in clinic. [11,14] Michel et al. have futher detamined that the proximal cluster perforators of radial artery located at a distance of 61.7 percent along the radial styloid-to-lateral epicondyle interval in an anatomical cadaver study. The perforators reveal no statistical difference in either radial or ulnar distribution originated from the radial artery. In our study, an anastomosable perforator originated from the radial artery can be always detected in all volunteers' proximal forarm. This perforator location at about 8.8 cm far from the elbow crease, and the relative distance is about 37.2% along the elbow crease to wrist crease interval, which is consistent with the previous study. Furthermore, this perforator is an intermuscular septal type coursing between the brachioradialis and the pronator teres muscles, and the pedicle length is 12 mm, the internal diameter is 0.7 mm under ultrasonography. These ultrasonography data illustrate the perforator is consistently located at the radial artery in the proximal half of forarm, and designing a free flap based on this single perforator could be achieved. Furthermore, the diameter of the perforator can match with digit artery well in the reconstruction of finger. The multiple superficial veins in forarm can be harvested as an alternative donor vein for venous drainage. Our study is also proved the importance of ultrasonography preoperatively. Ultrasonography is an simple and noninvasive inspection method to locate an small perforaor for desiging a flap. So we suggest the perforator inspection and location using ultrasonography should be an routine examination before a flap operation.
How much aera could the free flap based on a single perforator of radial artery be done? According the anatomical study about proximal perforators of radial artery, several perforators coming off the radial artery travel to the skin and form linking networks with each other along the radial arter as axis (about 2 cm wide). [11] This network of vessels between the fascia and the dermis ensure the adequate blood supply for designing a long free flap(10 cm-18 cm reported by Lin JY [16] ), meanwhile, There are several limitations in this report. First, we could not perform objective examination for precise marking the perforator directly and evaluating blood supply area of a single perforator.
Second, the population sample is not large enough in ultrasonography study, and the clinical implications of radial artery proximal perforator free flap are limited.

Conclusions
There is an anastomosable perforator consistent located on the radial artery in the proximal half of forarm. Preoperative detection and locating this perforator using ultrasonography can facilitate elevation of the flap. With the consistent anatomy of perforator and the satisfactory outcome in clinic application, the free radial artery small flap based on a single perforator (preservation radial artery) is a reliable and useful option for reconstruction of digital defect.  Diameter: The internal diameter of the perforator vessel of radial artery measured by e ultrasonography .
Pedicle Length: The pedicle distance from its origination of radial artery to deep fascia by ultrasonography.

D p :
The distance from location of the perforator to the elbow crease.

D E-W :
The distance fromthe elbow crease to the wrist crease.
Perforator Location = D p / D E-W ×100%: The relative distance of the perforator location beyongd the elbow crease.   The location of the perforator of the radial artery in the proximal forearm. P:perforator; Dp: The distance from location of the perforator to the elbow crease; DE-W : The distance fromthe elbow crease to the wrist crease. Perforator Location = Dp / DE-W ×100%: The relative distance of the perforator location beyongd the elbow crease.