The ulnar digital artery perforator flap for little finger defects: Using the abductor digiti minimi as a landmark – Surgical technique

INTRODUCTION

Numerous techniques have been proposed to address the little finger palmar defects, each with its own set of advantages and limitations.^[1-9] Skin grafts, while straightforward, require a suitable wound bed without exposed bones or tendons and often result in suboptimal cosmetic results. Various free flaps have been employed to cover ulnar defects.^[1-9] However, these flaps often leave notable donor-site defects, necessitate the sacrifice of a major artery, and may require additional procedures for thinning or reshaping.

Local flaps, such as the cross-finger flap and the reverse ulnar hypothenar flap, have also been utilized. The drawbacks are the need for a second surgery and sacrificing the volar digital artery of the little finger. Local perforator flaps have recently been preferred due to their reliability, thinness, and reduced donor-site morbidity. These flaps leverage the reliable vascular network of the hypothenar region, where consistent perforator vessels are likely to be present.

This study focuses on using a pedicled perforator flap from the ulnar digital artery to reconstruct soft-tissue defects on the volar aspect of the little finger. Specifically, it presents the abductor digiti minimi muscle as a landmark for perforator identification, which may be considered a standard and effective method for locating perforators. The aim was to detail the planning and harvesting techniques and to demonstrate the range of coverage achievable with this flap.

Anatomical details of the ulnar digital artery perforator (UDAP) flap

The hypothenar region, known for its rich vascular network, has garnered significant attention as a potential donor site for both local and free flaps aimed at covering hand defects. Several studies have investigated and documented the vascular supply in this area, providing a foundation for its use in reconstructive surgery.

Research has identified the hypothenar region as a reliable donor site due to its consistent vascular supply, particularly from the ulnar digital artery.^[1-9] Plancher et al.^[1] highlighted its use in failed carpal tunnel syndrome, demonstrating the viability of this area for flap harvest. In addition, Kinoshita et al.^[2] and Kojima et al.^[3] confirmed the utility of the subcutaneous pedicle and reverse pedicle flaps in the hypothenar region.

Specifically, Omokawa et al.^[4] identified the constant vascular supply from the ulnar digital artery, which provides a reliable and consistent blood supply, making it an excellent candidate for the development of perforator flaps.

The UDAP flap is designed based on perforators that emerge from the ulnar digital artery, ensuring a robust and dependable blood flow. These perforators allow for the creation of a flap that is thin, pliable, and well-suited for covering defects in the volar aspect of the little finger, providing both functional and esthetic benefits with minimal donor site morbidity.

INDICATION AND CONTRAINDICATIONS

The UDAP flap is ideal for reconstructing various defects. It is particularly effective for post-burn contracture defects, providing an excellent solution for restoring damaged areas resulting from burns.^[5-7] In addition, it can be used to cover traumatic defects, offering reliable coverage for wounds caused by injury. The flap is also suitable for reconstruction following Dupuytren’s contractures’ release, helping restore function and appearance. Furthermore, it provides reliable coverage for amputation stumps of the little finger.

The presence of a painful neuroma may be considered as a contraindication. Inadequate subcutaneous fat padding is another contraindication, as insufficient fat may increase the risk of a painful scar or neuroma. Patients prone to significant edema and congestion may not be ideal candidates, as these issues can affect the viability of the flap. Finally, in cases of hand burns with multiple finger contractures and significant dorsal involvement, alternative flaps may be more suitable for reconstruction.

PRECISE MARKING

Use a hand-held Doppler to accurately identify and mark the UDAP before surgery to ensure precise flap design. For a distal-based flap, the perforators are identified close to the distal palmar crease. For a proximal-based flap, multiple large perforators are identified, and an intraoperative decision to sacrifice perforators depends on the flap mobility and arc of rotation to cover the defect.

ANESTHESIA AND PATIENT POSITIONING

The patient is positioned supine and undergoes surgery under supraclavicular brachial block anesthesia, with an upper arm tourniquet applied. Informed consent is diligently acquired from all patients, with active involvement of their relatives in the decision-making process. To ensure precision during the flap harvest, the procedure should be performed under magnification and tourniquet control.

SURGICAL TECHNIQUE

Illustrative case

A 14-year-old girl presented to us with a severe flexion contracture of her right little finger, significantly restricting her daily activities. She had sustained a burn injury at the age of 2, resulting in wounds over the volar aspect of the right little finger. Without treatment, the burns led to the development of a severe flexion contracture that progressively restricted her activities and affected the cosmetic appearance of her hand. Clinical examination revealed an inability to extend the little finger passively due to severe flexion contracture [Figures 1 and 2]. Radiographs showed a proximal interphalangeal joint flexion of more than 90°.

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Figure 1:

Clinical picture of a 14-year-old girl with severe flexion contracture of the little finger following burns.

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Figure 2:

Clinical picture showing a fixed flexion contracture of the little finger.

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Considering the severity of the contracture and the need for extensive flap coverage, the UDAP flap was selected as a single-stage procedure. Before surgery, the UDAP was marked using a hand-held Doppler [Figure 3]. During the operation, the flexion contracture on the volar aspect of the little finger was released, exposing the flexor tendons and neurovascular bundles [Figure 4]. The little finger was straightened and maintained in position with a Kirschner wire.

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Figure 3:

Doppler markings of the perforator guiding us to the distal perforator from the ulnar digital artery.

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Figure 4:

The defect following contracture release, requiring the ulnar digital artery perforator flap.

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The UDAP flap was elevated as a distal-based flap, with a consistently large perforator identified over the musculotendinous portion of the abductor digiti minimi [Figures 5 and 6]. The flap was, then, rotated 180° to cover the flexor defect on the little finger [Figure 7]. The donor site was closed primarily, and sutures were removed two weeks post-surgery. The little finger was immobilized with a splint for three weeks, after which the Kirschner wire was removed and physical therapy was initiated. At six weeks follow-up, the girl achieved a good range of motion in the little finger [Figures 8 and 9]. She returned to school and had a full range of movements at the final six-month follow-up.

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Figure 5:

Intraoperative picture showing a reliable distal perforator over the musculotendinous junction of the abductor digiti minimi.

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Figure 6:

Illustrative diagram of the flap showing the distal perforator located over the musculotendinous portion of the abductor digiti minimi.

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Figure 7:

Immediate postoperative picture of the flap and little finger stabilized with a Kirschner wire to maintain deformity correction.

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Figure 8:

Final follow-up picture with a well-settled flap over the flexor aspect of the little finger.

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Figure 9:

Final follow-up picture with the little finger extended and no donor site morbidity.

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In the authors’ series of six patients, there were four cases of post-burn contracture, one case of post-traumatic contracture, and one non-healing wound. All flaps healed well without any complications or donor-site morbidity.

DISCUSSION

Hwang et al., in an anatomical examination of 18 cadaveric hands, identified consistent cutaneous perforators (ranging from 1 to 3) originating from the ulnar artery approximately 20.0 ± 7.0 mm distal to the pisiform.^[8] However, locating the perforators using measurements from the pisiform is challenging. Uchida et al. observed 3–7 branches (an average of five) stemming from the ulnar digital artery. They noted at least one perforator within 9 mm of the metacarpophalangeal (MCP) joint, which they used as an anatomical landmark.^[7] However, the anatomy and location of the MCP joint can vary between individuals, making it difficult to identify the perforators based on the MCP joint clinically and intraoperatively.

Toia et al., in their study of 14 cadaveric hands, used the proximal edge of the A1 flexor pulley as a landmark and described three to six perforators originating from the ulnar digital artery of the little finger and one to two from the ulnar artery, with distances ranging from 0 to 0.5 cm from their landmarks.^[9] However, there is a risk of injuring the perforator or the distal neurovascular bundle while identifying the A1 pulley to locate the perforator. This study did not assess the venous supply to the flap but recommended a cuff of adipose tissue around the pedicle to ensure venous flow [Table 1].

In a preliminary report, Panse and Sahasrabudhe described 3–4 perforators that arose from the ulnar digital artery, with the most distal perforator located 3–5 mm distal to the distal palmar crease.^[10] Due to individual anatomical variations, the distal palmar crease cannot reliably serve as a landmark for locating the UDAP.^[11,12]

Our study identified a consistent perforator over the musculotendinous portion of the abductor digiti minimi, proposing this as a reliable landmark for distal-based perforator flap elevation in little finger defects. Relying solely on measurement values and reference points such as the MCP joint, A1 pulley, or distal palmar crease can be problematic due to individual anatomical variations. Instead, the abductor digiti minimi muscle, which culminates in a tendon at the musculotendinous region, consistently reveals a larger and safer perforator from the ulnar digital artery, making it a dependable guide for flap elevation.

Our study offers easily identifiable landmarks to facilitate the design and elevation of the UDAP flap. However, it should be noted that we did not provide evidence demonstrating the superiority of our marking method over previously described techniques. Further, research is necessary to validate the effectiveness and reliability of these landmarks in clinical practice.

CONCLUSION

The ulnar digital artery perforator (UDAP) flap presents a reliable and effective option for reconstructing soft tissue defects in the little finger. Its consistent perforator location over the abductor digiti minimi muscle provides a dependable landmark for flap harvest. This flap offers several advantages, including a single-stage procedure, thin and pliable coverage, minimal donor site morbidity, and favorable cosmetic outcomes. However, surgeons should be aware of potential pitfalls such as perforator spasm, digital artery injury, and postoperative venous congestion.

While further research is needed to validate the superiority of the proposed landmark over existing techniques, the UDAP flap represents a valuable tool in the reconstructive surgeon’s armamentarium for addressing little finger defects. By understanding its anatomy, indications, contraindications, and surgical nuances, surgeons can effectively utilize this flap to achieve optimal functional and aesthetic results for their patients.