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

Objectives: To locate the anastomosable constant perforator of radial artery on the proximal forarm using ultrasonography, and describe the application of free radial artery �ap 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 �aps 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 �aps 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, the mean Brief Michigan Hand Questionnaire (BMHQ) score was 72.9 (60.4-85.4) in the affected hand. Conclusions: There is an anastomosable perforator consistent located on the radial artery in the proximal half of forarm. The free radial artery small �ap based on this single perforator provides acceptable functional and cosmetic outcomes for the reconsturction of digital soft tissue defects . With the preservation of the main vessel (radial artery) of forearm, this �ap provides another reliable option for handsurgery surgeon to reconstruct small digital defects.


Introduction
There are many options for reconstruction of soft tissue defects in the ngers, such as traditional or regional pedicled aps and free aps, while the reconstruction of small digital defects (especially multiple digital defects) still presents a challenge to the hand surgeon.[3] Various small free aps can be harvested from thenar, forearm (including arterialised venous ap), groin, partial toe and plantar of foot to reconstruct small digital defects in clinic, [4][5][6][7][8][9] while there is not golden donor site for digital defects reconstruction using the small free ap.
Howerer, either free or pedicle radial forearm ap which is havested as traditional surgical technique has the main limitations is that the ap must sacri ce a major axial artery for upper extremity.In 2004 and 2005,in order to preserve of the radial artery, Lin and Omer rstly attempted to havest proximal perforator clusters ap from radial artery of forearm to reconstruct head and hand defects,respectively. [16][17] Duplex ultrasonography is a well-known method of identi ng and evaluating the perforators for free ap 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 ap based on this single perforator in clinical cases to assess the ap'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 identi ed 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 identi ed and located with a 14L5 high-frequency 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 aps 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 ap was used to reconstruct one digital soft tissue defect, other digital soft tissue defects were reconstructed by orther free aps (such as super cial palmar branch of radial artery free ap or dorsal interosseous artery free ap).

Surgical Technique
Before the operation, the location of the perforator arising from the radial artery was determined and marked in the proximal half of forarm by ultrasonography.Under general anaesthesia or brachial plexus block anaesthesia, the patient was placed in a supine position, with the upper extremity 90 degrees abduction resting on a well-padded arm board.The operation was performed under pneumatic tourniquet control without limb exsanguination and under microscopic magni cation to permit better identi cation of the perforator vessels.After the devitalised tissue in the wound was debrided, the recipient vessels were prepared in the defect.Depending on the size, shape of the resulting defect, a free ap was drawn on the proximal forarm.The center of the ap was designed at the location of perforator entering into deep fascia, which was marked by ultrasonography pre-operatively.The axis of the designed ap was the line from the middle point of cubital fossa to the pulsation point of radial artery at styloid process.The ap elevation was started from the lateral border until the perforator vessel originating from the radial artery was detemined between the brachioradialis and the pronator teres muscles.Then the medial border of the ap was incised and retrograde dissection of the single perforator was conducted to the fascia where the pedicle arose.Another one subcutaneous vein should be preserved and havested into the designed ap to guarantee the venous return of the ap, and the branch of lateral antebrachial cutaneous nerve should be havested into the ap and anastomosed to a cutaneous sensorial nerve of the recipient site if possible.
Then the ap was completely elevated from the deep fascia.After releasing the tourniquet, the perfusion of ap was con rmed, the perforator pedicle can be divided at its origin from the radial artery and vena comitantes.The presevative subcutaneous vein was also divided according to desired length of recipient vein.The raised ap was placed on the digital defect, and the vessles of ap pedicle was anastomosed in an end-to-end fashion to the recipient vessles using 11-0 Prolene suture (Ethicon, USA) under the microscope.The ap margin was sutured to the defect margin, and the donor site of ap was closed primarily.

Postoperative Management and Follow-up
Standard postoperative free ap 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 Brief Michigan Hand Questionnaire (BMHQ) was used for evaluating the ap and the hand function in all the patients.The BMHQ contains 12 questions with a original score of 1 (poor) to 5 (ideal) regarding 6 domains of the hand function (overall function, daily life activities, work performance, pain, aesthetics and satisfaction), and then the original scores were nally calculated on a scale from 0 (poorest function) to 100 (ideal function) using the formula: 100×(BMHQ raw score-1)/4.Higher scores indicate better functioning and satisfaction. [18]sults

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%).( Tab. 1)

Clinical Result
The cases of ap were shown in Fig. 3-5.All the aps were harvested from the ipsilateral forearm, and the donor sites were closed directly.The size of the aps ranged from 3.5-6.5 cm to 2.3-3.0 cm.The diameter of the single perforator was 0.5-0.7 mm.There were no early complications (eg, infection, wound dehiscence, hematoma, and vascular congestion) in the cases and all the aps were survival completely.
During the follow-up period, no patient experienced cold intolerance, abnormal sensory, scar pain.There

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.[15] Howerer, either free or pedicle radial forearm ap remains the main disadvantage is that the sacri ce of a major artery to the upper extremity.
Generally, sacri ce 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.
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 ap 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 ap based on this single perforator in clinical cases to assess the ap's potential application for reconstruction of the digital soft tissue defect.
Several previous studies about the perforators analysis of radial artery have con rmed that two main clusters perforators ( ≥ 0.5 mm diameter; distal cluster and proximal cluster) in forarm could be potentionally used for ap 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 12mm, 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 ap based on this single perforator could be achieved.Furthermore, the diameter of the perforator can match with digit artery well in the reconstruction of nger.The multiple super cial 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 ap.So we suggest the perforator inspection and location using ultrasonography should be an routine examination before a ap operation.
How much aera could the free ap 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 2cm wide). [11]This network of vessels between the fascia and the dermis ensure the adequate blood supply for designing a long free ap(10cm-18cm reported by Lin JY [16] ), meanwhile, the wide of free ap is limited (usually ≤ 4cm).This shape feature of an oblong ap is especially suit to reconstruct the defect in long nger.There are some other more advantages of the radial artery proximal perforator free ap: tstly, the single perforator ap haversting preserves the radial artery avoiding the potentional ischemic problem of upper extremity; secondly, the ap can provide the similar colour and texture match and aesthetic apperance of the nger; thirdly, the lateral antebrachial cutaneous nerve can be havested into the ap to recovery excellent sensory of nger; lastly, the operation can be one stage performed in a single operative eld.
Brief Michigan Hand Questionnaire (BMHQ) is the brief version of MHQ established in 2011, which including six distinct domains (Overall function, Daily life activities (ADL), Work performance, Pain, Aesthetics and Satisfaction).Every patient needs to answer 2 questions in each domain (a total of 12 questions), each question is assigned a score from 1 (min=poorest) to 5 (max=ideal) regarding hand function evaluated by the patient, and then the average original score in each domain is calculated to generate a score that is scaled from 0 (poorest) to 100 (ideal).BMHQ has been demonstrated as a reliable and valid hand speci c instrument for evaluating hand function. [18]In this study, the average total score of BMHQ in four patients is 72.9 (range 60.4 -85.4), among of which the average satisfaction score is 87.5, the the overall function and ADL scores are 78.1.Thees data indicate that the hand function fully meets the needs of daily life for patients, and the patients are satisfaction with the hand function after the ap surgery.The work performance score and the pain score are both 62.5, that may attribute the compound tissue damage (including fracture, tendon injury, nerve injury) to limit the functional recovery of the affected hand.
There are also some disadvantages of the radial artery proximal perforator free ap, including: nonconcealed enough morbidity in donor site, bulkiness of the ap in the reconstructive nger, dissection and anastomosis of microvessels.The main morbidity in donor site is the presence of a longitudinal scar in the forarm, so the aesthetics scores self-evaluated by the patients in our study are lower than 70.Due to the small diameter of perforator (0.7 mm), meticulous dissection is required for ap elevation, and anastomosis requires supermicrosurgical skills.
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 ap 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 ap.With the consistent anatomy of perforator and the satisfactory outcome in clinic application, the free radial artery small ap based on a single perforator (preservation radial artery) is a reliable and useful option for reconstruction of digital defect.
No The score of every item is normalized on a scale from 0 (poorest function) to 100 (ideal function) as the formula: 100×(BMHQ original score-1)/4.The total score is the average of every item. The were no functional impairments and at the donor sites.The data of patients and outcomes were shown in Tab. 2. The average follow-up time was 12 months (range 8-14 months).The mean BMHQ total score in all the patients was 72.9 (range 60.4-85.4),including the overall hand function score was 78.1 (range 62.5-87.5), the activities of daily living score score was 78.1 (range 62.5-100), the work performance score was 62.5 (range 50-75), pain score was 62.5 (range 50-75), aesthetics score was 68.8 (50-87.5),selfsatisfaction score was 87.5 (range 75-100).The functional outcomes estimated by BMHQ of all the patients were show in Tab. 3.
perforator of Duplex ultrasound image: a perforator arising from the radial artery between the brachioradialis muscle and pronatorteres muscle in the proximal half of forarm.Diameter(+):The internal diameter of the perforator; Pedicle length(×): The pedicle distance from its origination of radial artery to deep fascia; RA: radial artery; P:perforator; BR: brachioradialismuscle; PT: pronatorteres muscle.