First Web-space Reconstruction Using the Second Dorsal Metacarpal Artery Cutaneous Flap: A Reliable Choice for Large Defects

Background First web-space defect reconstruction is challenging for reconstructive surgeons. The second dorsal metacarpal artery (SDMA) ap is useful in treating hand and nger defects. However, limited studies have used it for the rst web-space defects. This study reports a modied SDMA ap to treat rst web-space soft-tissue defects.


Abstract Background
First web-space defect reconstruction is challenging for reconstructive surgeons. The second dorsal metacarpal artery (SDMA) ap is useful in treating hand and nger defects. However, limited studies have used it for the rst web-space defects. This study reports a modi ed SDMA ap to treat rst web-space softtissue defects.

Methods
From April 2012 to October 2018, 8 patients underwent a modi ed SDMA ap transfer (mean ap size, 2 × 3 cm to 4 × 6 cm). The average length of the pedicle was 2.9 cm. On average, the ap was rotated 84°. In 6 patients, full-thickness skin was grafted at the donor sites. The donor site was primarily closed in two cases.

Results
All wounds were healed without complications of ap failure or donor area-related morbidity. The average follow-up period was 7.9 months, and these patients were satis ed with the functional recovery and cosmetic appearance of the scar area. At the end of follow-up, the average movement range of the metacarpophalangeal joint of the thumb, index nger, and long nger were 84°, 88°, and 87°, respectively, while those of the contralateral thumb, index nger, and long nger were 87°, 88°, and 85°, respectively. The rst web of the injured side spanned an average of 73°; the measurement on the contralateral side was 91°.

Conclusions
The SDMA ap reconstruction is a simple and fast procedure with a wide resurfacing range for large rst web-space defects, low donor-site morbidity, and good functional and esthetic appearance.

Background
An adequate rst web-space is required to maintain normal hand functions such as pinching, gripping, and prehension. Owing to its importance in hand movements, it is important to maintain the mobility of the rst web-space and prevent or minimize its contracture (1,2). First web-space defects can be treated with various reconstructive methods, including the dorsal metacarpal ap, posterior interosseous forearm ap, reversed ow radial forearm aps, reversed ulnar forearm ap, microsurgical anterolateral thigh ap, and skeletal traction(3). Z-plasty and local aps based on hand alone are ineffective in rebuilding large defects. Although skin grafts can cover most of the web-space defects, they cannot improve the functional aspect or produce a stable outcome. Moreover, contracture recurrence is often observed, which may necessitate a second surgery.
A variety of local aps has been reported to reconstruct web-space defects. However, they are inadequate to treat extremely large or deep defects. The posterior interosseous artery ap could be an alternative, but it is bulky, requires skin grafting, and leaves noticeable scars, which cannot be easily covered (3). Free and remote aps have also been recommended to reconstruct the soft-tissue defects of the web-space. However, these procedures require longer operating time, demand microsurgical expertise, and have the risk of anastomosis failure.
Pedicled aps have remained signi cant in reconstructive rst web-space surgeries as they follow the basic concept of ''like-with-like.'' In 1987, Earley, for the rst time, reported the usefulness of the second dorsal metacarpal artery (SDMA) ap for the treatment of rst web-space contractures (4). Several modi ed SDMA island aps have been described since. Quaba et al. reported the usefulness of a distally based dorsal metacarpal artery perforator ap for resurfacing web-space defects (5). Recent studies have reported the presence of additional communication arterial networks in the web-space and proximal phalanx, thereby providing newer options for ap design(6-9).
SDMA aps have been extensively used for treating hand and nger defects (10)(11)(12)(13). The SDMA ap has su cient and stable blood supply, a broad rotational arc, and low morbidity in the donor site. However, to our knowledge, limited studies have previously reported the use of SDMA ap to reconstruct large defects. It is reasonable to assume that the limited ap width restricts its use for extensive defects involving the rst webspace. Wang et al. reported the presence of transverse arterial communication networks among neighboring cutaneous branches of the dorsal metacarpal arteries (14), indicating that a modi ed ap may be designed based on transverse and axial arterial networks, extending beyond the adjacent metacarpal arteries. Signi cant advances have been made in identifying the arterial networks of SDMA, and many studies have reported promising results that could increase the width and length of the SDMA ap to improve, thereby improving the therapeutic strategies for restoring large defects of the hand. Based on the above-mentioned studies, the authors describe a novel, modi ed design of the SDMA ap for rst web-space defects reconstruction.

Methods
From April 2012 to October 2018, a modi ed SDMA ap transfer was performed in 8 hands of 8 patients (5 men and three women). The etiologies of injury were degloving (n = 1), burn (n = 1), avulsion (n = 4), and crush (n = 2). All cases of web-space defects were reconstructed with SDMA aps. The demographic and surgical details of the patient are summarized (

Operative technique
Under plexus block or general anesthesia, the patient was placed in a supine position. A Doppler ultrasound was performed to assess the SDMA and locate the pedicle position. The acute wounds were debrided, and the skin ap was outlined according to the area of the recipient site. At approximately 1.0 cm close to the second metacarpophalangeal (MCP) joint, Doppler ultrasound was used to detect SDMA bifurcation and its distal dermal branch. The pedicle was positioned along the distal cutaneous branch of the SDMA, which ows proximally between the rst and third metacarpals. The initial incision was cut along the margin of the ap. The maximum ap size included the dorsal skin of the MCP and carpometacarpal joints, and that between the marginal lines of the rst and fourth metacarpals (Fig. 1). The edges of the ap were incised and elevated from the proximal to the distal direction in the subcutaneous plane. The pedicle, along with the subcutaneous tissue, was dissected distally between the second and third metacarpals. The cutaneous branch of the SDMA close to the pivotal point was also ligated or transected to ensure continuity of the cutaneous branch (Fig. 2).
After surgical debridement, the ap was rotated to the recipient site through an open incision or a subcutaneous tunnel. The donor site was primarily closed or resurfaced with skin grafting. Postoperatively, the ap was monitored visually for seven days to assess tissue color and capillary re lling. The thumb was immobilized postoperatively for 12-14 days with a protective splint.

Outcome evaluation
At the end of follow-up (range, 4-12 months), the range of motion (ROM) of the hand was measured three times using a goniometer, and the mean value was calculated. Web span was measured with the thumb and ngers in maximal abduction. These measurements were compared to those obtained for the contralateral hand. Postoperative scar pain at the donor sites and the rst web-space were assessed using a visual analogue scale (VAS; a 10-cm horizontal line). Hand appearance and function were assessed by a single assessor using the Michigan Hand Outcome Questionnaire.

Results
The mean age of the patients at ap transfer was 42.6 years (range, 26-59 years) old. The ap sizes ranged from 2 cm × 3 cm to 4 cm × 6 cm, and the mean pedicle length was 2.9 cm (range, 2.5-3.3 cm). The aps were rotated by an average of 84° (range, 75-90°). In 6 cases, the donor area was grafted with a fullthickness skin graft, while the donor site was primarily closed in two cases.
The wounds in all patients healed uneventfully and without any ap complications, such as arterial insu ciency or venous congestion. No patient manifested any apparent donor site-related morbidity. The mean follow-up period was 7.9 months (range, 4-12 months), and all the patients were satis ed with the postoperative functional outcomes and the appearance of the donor site scars.
At the nal follow-up, the average ROMs of the MCP joint of the thumb, index nger, and long nger were 84°, 88°, and 87°, respectively; those of the contralateral thumb, index nger, and long nger were 87°, 88°, and 85°, respectively. The average span of the rst web on the injured side was 73°, while that on the contralateral side was 91° (Table 2). The results of postoperative pain assessment by VAS showed that only one patient reported pain at the rst web-space (VAS score, 2). No patient reported scar pain at the donor site. Seven patients were satis ed with the aesthetic result of the ap and donor site of the hands according to the outcomes of the Michigan Hand Outcome Questionnaire. One patient experienced occasional discomfort with their hand appearance. All the patients were satis ed with both the ROM of ngers and hand strength.

Case 1
A 37-year-old woman was hospitalized after an avulsion injury of the rst web-space of her left hand (Fig. 3).
After surgical debridement, a pedicled SDMA ap (3.5 cm × 4.8 cm) was dissected in a proximal-to-distal direction, rotated by 75°, and then rotated to cover to the injury site via a subcutaneous tunnel for rst webspace reconstruction. The mean pedicle length was 2.5 cm. A full-thickness skin transplantation was conducted on the donor area (Fig. 4). Postoperatively, the wounds healed uneventfully, with complete ap survival. Results at postoperative 6-month follow-up indicated an aesthetic result of the ap (Fig. 5).

Case 2
A 48-year-old man was admitted to our hospital due to a crush injury. A 3.5 × 5.5-cm defect remained after wound debridement, for which a free lateral arm ap was initially planned. However, the ap failed, presumably because of arterial thrombosis. Therefore, a 4 × 6-cm salvage SDMA cutaneous ap was designed. The ap was rotated 90° to resurface the rst web defect (Fig. 6). Thereafter, the skin harvested from the lost ap was grafted to the dorsum of the hand. The patient had an uneventful postoperative recovery without venous congestion, infection, or necrosis of the ap. Follow-up assessment at postoperative two months demonstrated an excellent result, with an improvement of the esthetic appearance. ROMs of the thumb, index, and long ngers of the injured hand were comparable to those of the contralateral hand. The patient's postoperative pain score was 0 on VAS, and he was fully satis ed with the outcome (Fig. 7).

Discussion
First web-space defect-a common sequela of hand trauma-can be caused by injuries, burns, paralysis, and infection. This defect has a profound adverse effect on the hand function, as even a slight contracture will result in decreased thumb mobility. The present study investigated the usefulness and postoperative outcomes of a novel, modi ed SDMA ap technique to treat rst web-space soft-tissue defects in eight patients. This modi ed technique conferred good postoperative outcomes and an acceptable esthetic appearance. The donor area was closed directly in two cases, while those in six cases were resurfaced with skin grafting. The modi ed SDMA ap technique is timesaving, without causing any ap loss. Moreover, neither ap necrosis nor a web contracture was seen.
When selecting donor sites for the reconstruction of the web-space, the hand itself is preferable to other sites due to various advantages, including "like-with-like" tissues, superior recovery of sensitivity, and the requirement for a limited surgical area in a single anatomic region. Therefore, pedicled aps remain important in reconstructive rst web-space surgeries. The rst dorsal metacarpal artery ap was commonly used for web-space defects (15,16). Doğan described new bio-geometric designs of rst dorsal metacarpal artery ap-bilobed or V-Y advancement ap-to reconstruct soft-tissue defects of the rst web-space and the proximal dorsal thumb (17). This technique is generally indicated for complex defects. The contraindications of this technique include overlapped injuries to the donor region or to the pathway of the rst dorsal metacarpal artery. The rst dorsal metacarpal artery ap is also limited by the small size (up to 4 cm), which may not be large enough to cover most of its hand defects (18). Zhang et al. described the use of the SDMA ap to repair thumb defects. The ap sizes ranged from 3.5 cm × 3 cm to 3 cm × 3.5 cm (19). If the ap goes beyond the proximal interphalangeal joint, the ap survival may not be reliable. This technique is more suitable for the coverage of small-sized web-space defects. Zhu reported the use of bilobed SDMAbased island ap for the reconstruction of complex soft-tissue defects around the MCP joint of the thumb, which was harvested from both the index and long ngers (20). The average size of the aps from the index and long ngers was 2.6 cm × 3.4 cm and 2.8 cm × 3.2 cm, respectively. However, the disadvantages include a relatively complicated procedure and partial sensory impairment at the donor ngers.
To our knowledge, only a few studies have previously reported the use of SDMA ap to cover rst web-space defects. Presumably, the limited ap width may restrict its use for larger defects involving the rst webspace. However, our technique could offer a reliable chance for the reconstruction of the rst web-space defects. The ap margins were outlined proximally and distally to preserve the dorsal skin of the MCP and carpometacarpal joints, respectively, and between the marginal lines of the rst and fourth metacarpals. The cutaneous perforators of the SDMA have consistent ascending and descending branches. The adjacent ascending branches were anastomosed with the adjacent descending branches to form the axis of the cutaneous chain, which was parallel to the SDMA (14,21). Notably, there is a consistent anastomosis between the dorsal metacarpal arteries to form the transverse arterial network. Usually, the ap pedicle is su ciently wide to cover the recipient area without any tension (14). In this study, 4 × 6-cm aps were harvested. Moreover, the aps were narrowly rotated (by over 90°) to cover the web-space defect and to reduce the risk of venous insu ciency. This ap is reliable and versatile, simple and fast, has low donor site morbidity, and provides acceptance appearance cosmetically.
The advantages of this technique are the extended ap length and width, small rotation, low donor site morbidity, appropriate ap thickness, a low rate of ap failure, and almost near-physiological skin texture at the recipient area. Moreover, postoperatively, during the follow-up period, the patients' thumbs had the freedom of movement in any direction, and there were no sensorial complaints of the resurfaced anatomical parts. However, our study had a limited number of patients to assess the effectiveness of our aps.

Conclusion
In conclusion, our modi ed SDMA ap is a simple and fast procedure with a wide resurfacing range for large rst web-space defects, low donor site morbidity, and good functional and esthetic results. Moreover, the ap pedicle was su ciently wide to reach the rst web-space without any tension. Thus, the SDMA ap technique could offer a reliable chance for the reconstruction of rst web-space defects. Informed consent was required and obtained from the participants.

Con icts of interest
The authors declared that they have no con icts of interest in this work.

Funding
Not applicable