Reconstruction of Digital Defects with the Free Proximal Ulnar Artery Perforator Flap

Background:

The aim of post-traumatic digital reconstruction is to restore form and function, allowing early rehabilitation. In the absence of feasible local options, free tissue transfer can be a versatile and reliable alternative. The aim of this study was to describe our experience with the use of the free proximal ulnar artery perforator flap (PUPF).

Methods:

Our prospectively maintained free flap database was inquired for patients that had undergone digital reconstructions with free PUPFs.

Results:

Six patients that underwent digital reconstruction were eligible. The ipsilateral forearm was donor site of choice, with all flaps based on a perforator of the ulnar artery, without the need to compromise the main vessel. A superficial vein was routinely included with the flap. No flap failures were encountered. Mean hospital stay was 5.5 days, and all patients achieved a satisfactory functional result.

Conclusions:

The proximal ulnar perforator free flap offers an alternative for finger reconstruction, having the advantage of including thin and hairless skin from the proximal ulnar forearm. The vascular anatomy of the ulnar perforators seems to be constant. Furthermore, donor site morbidity is low, as the ulnar artery is not harvested with the flap, the donor site defect can generally be closed directly, and the scar is well concealed.

Takeaways

Question: Is the free proximal ulnar artery perforator flap a good option for digit reconstruction?

Findings: The results show that the free proximal ulnar artery perforator flap is a reliable flap which provides thin and hairless skin.

Meaning: The free proximal ulnar artery perforator flap could be a good option to reconstruct digital defects.

INTRODUCTION

Achieving timely soft tissue cover for traumatic digital wounds is crucial for ensuring healing of the damaged deep tissues and starting early rehabilitation. Functional and aesthetic considerations are important when selecting a reconstructive modality. An ideal reconstruction should not only resemble the quality of the lost skin, but also have in mind the functional result and the impact of any potential donor sites.

Homodigital^1–4and heterodigital^4–6flaps can be reliable local alternatives, offering simpler solutions for smaller defects.⁷ However, these are associated with donor site morbidity, either from the same or adjacent fingers.⁸ This inevitably can result in additional scars, potential swelling and stiffness within an already injured hand. Propeller and pedicled flaps from the dorsum of the hand and forearm have also been described,^9–11 but these rarely reach the distal segments of the fingers. These limitations explain why there has been an increasing interest in the use of free tissue transfer for resurfacing complex digital wounds.^7,8,12–18

The ulnar artery supplies the medial skin of the forearm via multiple perforators, most of which are musculocutaneous.¹⁹ On average there are five to seven ulnar artery perforators with a caliber equal to or greater than 0.5 mm, and an average length of 27 mm. Each perforator is able to nourish an area of skin of approximately 19 to 33 cm².^20–23

Most anatomical studies have shown that there are constant ulnar artery perforators between the proximal third and the middle third of the forearm, in the middle of the forearm, and between the middle third and the distal third of the forearm.^22,23 Proximally, these tend to have a musculocutaneous course within the muscle bellies of the flexor carpi ulnaris or the flexor digitorum superficialis, perforating the fascia along a longitudinal axis that follows the course of the medial cutaneous nerve of the forearm.²⁴ This perforator has demonstrated to supply an area of skin in the proximal ulnar forearm that can be harvested as a free flap.

The aim of this study was to describe our experience with the use of the free proximal ulnar perforator flap (PUPF) in the reconstruction of digital defects.

MATERIALS AND METHODS

A review of our prospective free flap database was undertaken, including all patients that had a proximal ulnar artery perforator flap for reconstruction of digital injuries. Demographic data, along with information regarding the causing injury and reconstruction modalities, were recorded using a predefined gathering spreadsheet. Functional outcomes, photographs, and patient satisfaction were also recorded.

From July 2019 to September 2019, six proximal ulnar perforator free flaps were used for the reconstruction of six digital defects by the first author. The alternative of having an amputation of the affected digit and its benefits and drawbacks compared with a reconstruction were routinely discussed preoperatively. All patients were men, with a mean age of 39.5 years, ranging from 13 to 63 years of age. For all cases, only one finger was reconstructed with a free PUPF.

Five patients suffered crush injuries and one sustained degloving of his digit. The size of the defects ranged from 4 × 3.5 cm to 11 × 3 cm. All cases presented not only by a skin defect but also associated soft tissue and bony component (Table 1). The size of the flaps raised ranged from 4 × 3.5 cm to 9 × 7 cm with a pedicle length between 3 cm and 5 cm. For all these cases, a perforator of the ulnar artery between the proximal third and the medial third of the forearm was used, including a superficial vein for achieving venous drainage.

Table 1.

Case Series Included in This Study

	Sex	Age	Digit	Trauma	Wound (cm)	Associate Lesions
1	M	31	III	Crush injury	11 × 3	P3 necrosi + partial necrosis P2
2	M	13	IV	Crush injury	5 × 3	P3 amputation
3	M	63	II	Crush injury	4 × 3.5	Ostheomyelitis P2
4	M	31	I	Crush injury	7 × 3	Intrarticular fracture (IF) + EPL laceration
5	M	45	III	Ring avulsion	9 × 3	None
6	M	54	IV	Crush injury	7 × 4	Crush injury II digit, amputation P3 III digit, laceration V digit

DVT prophylaxis, as well as antibiotic and pain killers were prescribed postoperatively. Bed rest was indicated for 3 days. For fractures stable enough to be mobilized, rehabilitation started 2 weeks following surgery.

SURGICAL TECHNIQUE

The ipsilateral forearm of the injured finger is preoperatively marked by drawing a line between the pisiform bone and the medial humeral epicondyle. Subsequently, the point between the proximal third and the middle third is identified and marked. The actual presence of a perforator in the established area is assessed with a handheld Doppler probe. We routinely use a thermal camera (FLIR ONE, FLIR Systems. Oregon) for assessing the chosen perforator along with the presence of superficial veins (Fig. 1).

Fig. 1.

Preoperative photograph showing marking of the flap, including a previously identified perforator. A superficial vein is marked with a green line.

With the patient supine and under general anesthesia, adequate wound debridement is followed by a careful assessment of the defect size and shape. Using reverse planning, the shape of the required flap is drawn on the donor site (Fig. 2). We routinely use a tourniquet-control for harvesting this flap. A second surgeon is able to prepare the recipient vessels while the flap is being raised.

Fig. 2.

Case involving a patient that sustained a degloving injury to his right third finger. A, B, preoperative dorsal and pal-mar views. C, Flap markings. This shape was designed to avoid straight scars along the digit with a round distal extension to cover the tip. D, The detached flap with its perforator (→) and superficial vein (★).

An incision along the radial margin of the planned skin paddle is used to expose and incise the fascia. Dissection proceeds ulnarly in the subfascial plane until a suitable perforator is seen in its course toward the skin (Fig. 3A). If necessary, the flap design can be adjusted at this stage. The perforator is then followed between the flexor carpi ulnaris and the flexor digitorum superficialis muscles or through the flexor carpi ulnaris muscle belly and isolated from the surrounding tissues up to its point of origin from the ulnar artery (Fig. 3B). One or more superficial veins are always included in the flap, while aiming to preserve the medial cutaneous nerve of the forearm.

Fig. 3.

Intraoperative views. A, perforator (→) . B, perforator (→) identified between the flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS) tracked up to the ulnar artery.

Once the flap has been harvested, the tourniquet is released to evaluate the perfusion of the flap. (See Video 1 [online], which shows the flap reperfusion after tourniquet releasing.) Only when the vascular perfusion of the flap is stable, the pedicle is divided flush on its origin from the ulnar artery (Fig. 4), and the flap is transferred to the recipient site. The recipient vessels usually are a dorsal vein of the injured finger or of the hand and a digital artery, usually ipsilateral to the defect. For the venous anastomosis, the superficial vein of the flap is always preferred due to its larger caliber.

Fig. 4.

Intraoperative photograph showing the detached flap with its perforator (→) and superficial vein (★).

Video 1. Flap reperfusion after tourniquet releasing. Video 1 from “Reconstruction of Digital Defects with the Free Proximal Ulnar Artery Perforator Flap (PUPF)”.

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RESULTS

In all cases, it was possible to intraoperatively find the perforator that had been identified using thermography. Sometimes a small discrepancy was reported between the supposed position of the perforator and the effective localization; in no one case did this force a plan change, but a partial change of the flap position was sufficient.

In five cases, a digital artery was used for the anastomosis, while in one case the dorsal branch of the radial artery was used in an end-to-side fashion. Similarly, in five cases, a dorsal superficial digital vein was used, and in one case, the vena comitans of the dorsal branch of the radial artery was used as recipient vein. In three cases, the donor site was closed directly, while in the other three a dermal substitute was used in combination with partial primary closure (Table 2).

Table 2.

Reconstruction Performed for Each Case, including Flap Characteristics, Microsurgical Technique, and Donor Site Closure Method

	Flap Dimension (cm)	Pedicle Length (cm)	Recipient Artery	Stitch Size and Anastomosis Technique	Recipient Vein	Stitch Size and Anastomosis Technique	Donor Site Closure
1	11 × 3	4	UDA	11/0 E-S	Dorsal vein (MF)	9/0 E-E	Delayed primary closure
2	5 × 3	4	RDA	11/0 E-E	Dorsal vein (MF)	10/0 E-E	Dermal substitute
3	4 × 3.5	3,5	RDA	10/0 E-E	Dorsal vein (P1)	9/0 E-E	Direct closure
4	9 × 7	3.5	RA	11/0 E-S	Vena comitans	11/0 E-E	Direct closure
5	9 × 5	5	RDA	12/0 E-E	Dorsal vein (MF)	10/0 E-E	Dermal substitute
6	11 × 4	3	RDA	10/0 E-E	Dorsal vein (MF)	9/0 E-E	Dermal substitute

All the flaps survived without any partial or total necrosis. Re-exploration or revision surgery was not necessary. The mean postoperative hospital stay was 5.5 ± 0.8 days. Mean follow-up was 18.5 months (from 7 to 22 months) (Fig. 5). Functional assessment was evaluated by using the PRWHE instrument,²⁵ obtaining an average score of 14 out of 100 (ranging from 3 to 2.5) as all the patients achieved a good functional result (Table 3). (See Videos 2 and 3 [online], which show the physiotherapist session 8 weeks postoperative.) (See Video 4 [online], which shows the functional result 8 weeks postoperative.) Regarding sensation recovery, all patients were satisfied; no signs of neuroma formation or cold intolerance have been detected to date. The subjective result from the aesthetic point of view was considered very good by one patient, good by four patients, and sufficient by one patient. No one patient complained about the thickness of the flap, and a debulking procedure was never necessary. No patients have complained of paresthesia in the donor forearm, and no sensitivity or strength deficit in the ipsilateral hand and forearm were reported.

Fig. 5.

Results of case described in Figure 2. A, The immediate postoperative result. B–D, illustration of the outcome after 7 months.

Table 3.

Postoperative Follow-up for the Patients Included in this Series

	Complications	Length of Stay (days)	Follow up (mo)	PRWHE Score
1	None	5	22	12.5
2	None	7	21	3
3	None	6	21	6.5
4	None	36	21	21.5
5	None	5	19	19
6	None	5	7	21.5

Video 2. Physiotherapist session 8 weeks postoperative. Video 2 from “Reconstruction of Digital Defects with the Free Proximal Ulnar Artery Perforator Flap (PUPF)”.

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Video 3. Physiotherapist session 8 weeks postoperative. Video 3 from “Reconstruction of Digital Defects with the Free Proximal Ulnar Artery Perforator Flap (PUPF)”.

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Video 4. Functional result 8 weeks postoperative. Video 4 from “Reconstruction of Digital Defects with the Free Proximal Ulnar Artery Perforator Flap (PUPF)”.

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DISCUSSION

The free ulnar artery perforator flap was originally described by Lovie et al.²⁶ It was based on the septocutaneous perforators of the ulnar artery and praised for its reliability, versatility, and ease of harvesting. This flap relied on a segment of the ulnar artery distally to the origin of the interosseous artery. Lovie highlighted the multiple advantages of this flap such as the absence of hair, the greater ease of direct closure of the donor site, and the minor evidence of the residual scar compared with radial artery-based flaps (Fig. 6). Another advantage of this flap is that if the donor site required skin grafting, better results were usually obtained due to the lack of tendon exposure in this area.^27,28

Fig. 6.

Donor site at 3 months follow-up.

Despite its extreme utility, the ulnar flap described by Lovie et al²⁶ involves the compromise of the ulnar artery. However, if only a short segment of the ulnar artery is harvested, the main vessel is still suitable for direct repair of the stumps.^29,30 This approach can be completely overcome by harvesting a true ulnar perforator flap, entirely preserving the ulnar artery.³¹

In our experience, the use of a proximal ulnar perforator flap has had multiple advantages. The skin in this area is thin, pliable, and hairless. The location of the donor site is more conceivable, in the medial proximal forearm. In addition, as the forearm is wider proximally, it allows the harvesting of larger flaps. The length of the flap may be extended so that with a single flap, a complete finger or two different wounds in two adjacent fingers may be resurfaced.²³ If a skin graft is required, tendon exposure is minimal in this area. Harvesting a sensory flap is possible if the medial cutaneous nerve of the forearm is included and the residual sensory deficit in the donor site is minimal, thanks to the presence of multiple cutaneous nerves in this area.^23,32,33 So far we have not raised a neurotized PUPF, and we aim to preserve the medial cutaneous nerve of the forearm.

This flap is suitable for raising under regional anaesthetic from the ipsilateral forearm. The ulnar forearm offers an excellent donor site for finger resurfacing, providing thin and hairless skin. It also has the advantage that flaps from this region can be harvested under regional anaesthesia if the ipsilateral forearm is selected as donor site. The contraindications for this flap would be a scarred proximal forearm and patients in which the ulnar artery is the sole vascular supply to the hand.

Our study is limited by the small sample included. So far, we have not encountered any flap failures, being able to preserve length in each of the reconstructed digits. The main disadvantage of this flap is the small diameter of the perforator, which requires exacting supermicrosurgical skills to perform the anastomosis. Harvesting a superficial vein of wider caliber can partially overcome this difficulty, offering an alternative drainage route for this flap. Another drawback is that flaps wider than 6 cm are not usually possible to close primarily. We have routinely used an acellular dermal matrix in these situations, but a skin graft is also a reasonable alternative.

CONCLUSIONS

The free proximal ulnar perforator flap is a viable option for the reconstruction of digital defects. The skin of the proximal forearm is well suited for this purpose as it is thin, pliable, and hairless. Morbidity at the donor site level has been low, as there is no need to harvest a portion of the ulnar artery. Adequate microsurgical training is required to anastomose small vessels. The residual scars on the forearm are well concealed.

ACKNOWLEDGEMENTS

The authors acknowledge the contribution of University Department of Hand Surgery & Rehabilitation (San Giuseppe Hospital – IRCCS MultiMedica Group Milan) physiotherapists, which have a fundamental role in our patients’ rehabilitation. They have kindly helped us measure the functional outcomes regarding the patients mentioned in this study.

INFORMED CONSENT

Written informed consent was obtained from the patients for their anonymized information to be published in this article.