The thumb is critical to hand function, and complete loss (amputation) of the thumb represents a 40% loss of hand function according to impairment rating conventions [1]. Adequate first web space is significant for the function of thumb. A contracted web space restricts thumb function, and a proper web space is indispensable for thumb abduction, web space expansion, and thumb mobility [2]. Many etiologies can induce web contracture, including trauma, burns, infection, paralysis, ischemia, spastic conditions, and improper splinting [3]. Many surgical techniques have been established to release web contracture using skin grafting, local flaps (Z-plasty, four-flap, or five-flap technique), first dorsal metacarpal flap, fill-up web flap, lateral arm flap, cross arm flap, groin flap, reverse posterior interosseous artery flap, and skeletal traction [4-6]. Each of these methods has its own advantages and disadvantages, and a surgeon must consider the recipient site condition, technical difficulty, and donor tissue similarity to determine the best plan. Cases with large defects after releasing all contracted structures require flap coverage to restore good function. The optimal donor site for web space reconstruction should be thin and pliable, easy to harvest and match the recipient site.

In our institute, we reconstructed the first web space using the wide-second dorsal metacarpal artery perforator flap (w-SDMAP flap) technique. The purpose of this study was to evaluate the results of the w-SDMAP procedure and to confirm the usefulness of the flap.

The mean flap size was 5.5 × 2.8 cm, with the smallest flap measuring 5.0 × 1.5 cm, and the largest flap measuring 5.0 × 6.0 cm (Table 2). All flaps were based on the w-SDMAP flap. Six flaps were designed in a transverse fashion, one flap was oblique, and one flap was rectangular. All flaps were transferred to the defective web space through a subcutaneous tunnel. The donor wounds of three flaps were closed directly, and five flaps required full-thickness skin graft (FTSG) or split thickness skin graft for closure. All flaps survived completely, and three of them survived following the salvage procedure. Two flaps required a subsequent defatting procedure. The mean postoperative angle of the first web space was 53º. The mean VSS score was 4 points (Table 2).

Adequate first web space is essential for hand function, and web space contracture can severely limit hand function. This study demonstrated that the w-SDMAP flap technique is useful in correcting large defects of the first web space. Aesthetic outcomes were acceptable, as measured by the VSS scores, and hand function was improved based on the postoperative improvements to the first web angle.

Many studies have assessed methods for measuring the angle of the first web space, but there is still no standardized method and no established normal angle. Fritsch used the intermetacarpal angle to measure the first web space and noted at least 45° as a normal web space angle [9]. Another study measured the distance from the thumbnail to the index metacarpophalangeal joint [10]. Jensen et al. [2] measured the first web space angle in normal volunteers using a goniometer and found that the mean angle was 100°. In this study, we outlined the web space on paper and then measured the angle using a goniometer [2]. Contracture of the first web space reduces the grasping ability of the hand and makes picking up small objects more difficult [2,11]. Many surgical approaches have been established to release web contractures, including skin grafts, local flaps (Z-plasty, four-flap, and five-flap technique), first dorsal metacarpal flap, fill-up web flap, lateral arm flap, cross arm flap, groin flap, reverse posterior interosseous artery flap, and skeletal traction [4-6]. Web space contracture can involve any combination of soft tissue components, including skin, fascia, intrinsic muscles, and ligaments. Accordingly, the principles of contracture release include adequate release of all tissues affecting contracture, lengthening of the contracted web, and resurfacing with additional tissue for a tension-free closure [11].

The dorsal metacarpal artery perforator (DMAP) flap was first described by Quaba and Davison [12], and it is a vascular island flap that is raised from the dorsum of the hand [13]. Because dissection is in the loose, areolar, and relatively avascular plane, which is superficial to the extensor paratenon, the DMAP flap is safe and easy to raise. Quaba and Davison [12] rotated the flap 90° in a propeller fashion when reconstructing the first web space. In this study, after releasing the first web space contracture, the coverage of the gross defect was needed. However, the traditional Quaba flap did not cover the palmar defect of the first web space. For this, a long pedicle was constructed using the adipofascial tissue between the perforator and flap, and then the defect was covered by moving the flap further away from the area where the perforator arose. Many anatomic studies have proven that the first and second dorsal metacarpal arteries are anatomically constant; thus, the flap has a safe pedicle source. The perforator arises just distal to the juncturae tendinum, and because it arises directly from the branches of the deep palmar arch, the DMAP flap can be raised even if there is no dorsal metacarpal artery [13-17]. Sebastin et al. [13] defined the indications of the DMAP flap in palmar defects up to the proximal half of the middle phalanx and dorsal defects up to the proximal distal interphalangeal joint. In that study, the distal edge of the extensor retinaculum was used as the distal limit for the DMAP flap because the distal DMAP can support the skin over the proximal half of the intermetacarpal space. A previous study set the distal edge of the extensor retinaculum as the distal limit. The average size of the flap was 4.6 × 2.3 cm, and the largest flap measured 6 × 4 cm [13]. In our study, the proximal edge of the extensor retinaculum was set as the distal limit, and all flaps survived perfectly. The average size of our flap was 5.5 × 2.8 cm, and the largest flap measured 5.0 × 6.0 cm. Our results demonstrate that a w-SDMAP flap can reconstruct the large first web space defect with a tension-free closure and a fingertip-width resurface defect. There are many methods to reconstruct the first web space, including free tissue transfer, such as a split groin flap, parascapular flap, lateral arm flap, and anterolateral thigh flap [18-20]. However, common drawbacks of these flaps are their bulkiness, mismatch of color and texture, microsurgical skill requirements, long recovery time, and postoperative immobilization [21]. By comparison, the harvest of the DMAP flap is fast and easy because it does not require microsurgery. An important goal of soft tissue reconstruction in hand defects is to regain normal or near-normal motion [22]. This requires thin, pliable tissue that allows thumb flexion and abduction. Another important consideration in selecting the tissue source is the principle of cosmetic units and subunits. The hand itself is better than other donor sites because it has better tissue match, texture, elasticity, thickness, and superior recovery of sensibility, and provides a single surgical anatomic field [21-23].

The disadvantages of the DMAP flap are a scar on the dorsal hand and the possible requirement of a skin graft to cover the donor site defect. The hand is a very visible and crucial part of human interactions and nonverbal communication [24-26]. Therefore, hand aesthetics are important to patients and may be a key factor when determining the donor site and estimating donor site morbidity. w-SDMAP flaps belong to distally based flaps with a special concern on venous drainage. To prevent venous congestion, sufficient adipofascial tissues around pedicles would be necessary. This flap has two venous systems; superficial venous system that drains from superficial tissues and deep venous system that drains from the retinacular microvenous connection [27]. In this study, venous congestion occurred in three cases, and flap survival was ensured after the salvage procedure.

There are many methods to assess scar quality, and the VSS is a tool that is widely used in many studies [7] (Table 1). In this study, the mean VSS score was 4 points. Our patients had near-normal thickness and vascularity values, which represent hypertrophic and pathologic scarring [28]. There was no distortion of the scar, and patients were satisfied with the scar appearance of the donor site. Nevertheless, preoperative informed consent is mandatory for postoperative scars on the hand dorsum. Furthermore, it would be better to use the skin laxity of the hand dorsum for aged patients than for young patients who are sensitive to scarring. As with conventional DMAP flaps [13], a preoperative check for deep lacerations, severe contusions, or metacarpal fractures around the vascular pedicle is essential.

The w-SDMAP is a useful technique for reconstruction of the first web space that is easy to raise, thin and pliable, and has excellent color and tissue matching. In addition, a w-SDMAP flap can reconstruct a large first web space defect with a tension-free closure and a minimal resurface defect.