Correction of thumb deformities after burn: Versatility of first dorsal metacarpal artery flap

1. Introduction 

Patients suffering from major burns frequently have hand involvement; it was reported that over 85% of burn victims have hand burns [1]. Sometimes because of ignorance of the hands during the management of a major burn or sometimes because of inappropriate treatment and rehabilitation, deep burns to hand may result in a great spectrum of hand deformities that impairs overall hand function depending on the part of the hand that was involved [2], [3]. The goal of reconstruction should be maximum restoration of hand function. Being the only opposing digit against the others, when the thumb is involved, functional loss may be more severe than anticipated. Eventually, because of its major contribution to overall hand function, correction of deformities involving the thumb is crucial. Adequate length, mobility, stability and sensation are the goals of a functional thumb reconstruction [4]. Mild to moderate contractures involving the thumb and adjacent thenar area can be corrected simply by release combined with the basic reconstructive techniques including skin grafting, variations of Z-plasty flaps and Y-V advancement techniques or combination while the severe contractures that cause a major deformity require more complex procedures such as local or regional flaps and even microsurgical transfer of partial toe elements [5], [6], [7], [8], [9], [10], [11], [12].

The skin overlying the dorsal aspect of the proximal phalanx of the index finger can be raised either as an island flap based on the first dorsal metacarpal artery (FDMA) or as a neurovascular island flap with inclusion of terminal dorsal sensory branches of radial nerve and can be transferred to reach and cover the defects of the both volar and dorsal aspects of the thumb and first web-space [13], [14], [15], [16], [17], [18]. After its anatomical details were first described in 1979, the FDMA flap has become popular among the surgeons dealing with thumb and first web-space reconstruction, owing to its certain advantages including sensory flap cover at one stage and reliable constant anatomy with the ease of dissection [13], [15], [16], [17], [18]. Anatomically, this flap is an axial pattern skin flap extending proximally from the level of metacarpophalangeal (MP) joint and distally to the level of proximal interphalangeal (PIP) joint and provides well-vascularized and sensory soft tissue with similar characteristics for replacement of the full-thickness defects involving the thumb and first web-space [15], [16], [17], [18].

In this article, our experiences with the use of FDMA flap for correction of the burn deformities involving the thumb and adjacent thenar area were presented along with the anatomical pitfalls of the flap harvest. Additionally, versatility of this flap in reconstruction of the burned hand was discussed.

2. Operative technique 

2.2. Flap design and harvest 

The skin island of the flap lies over the proximal phalanx of the index finger. The MP and PIP joint represent the distal and proximal extent of the skin island. The flap territory extends between midlateral lines on each side of the proximal phalanx of the index finger. After the outlines of the skin island are marked, a line is drawn along radial border of second metacarpal in a zig-zag or lazy-S fashion, beginning from the proximal base of the skin island and extending proximally up to the tip of the first web space (Fig. 1). Between the bases of the first and second metacarpal bone, the tip of the triangular first web-space can be palpated, indicating the most proximal point of the pedicle dissection. When marked, this point represents the pivot point of the flap. In order to predict where the flap can reach, maximum rotation arch of the flap design can be estimated by measuring the distance of PIP joint from this pivot point.

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Fig. 1. Patient 1. (A) Pre-operative view of the hand; burn contracture that cause severe deformity. (B) Flap design: the skin island of the flap lies over the proximal phalanx of the index finger. (C) The flap was elevated on pedicle including FDMA, superficial dorsal vein and a terminal branch of dorsal sensory branches of the radial nerve. (D) The harvested island flap was transposed onto the defect through a skin tunnel and donor site is resurfaced with a skin graft. (E, F) Post-operative view at 6 months following the operation.

This flap can either be elevated in a distal to proximal fashion without prior pedicle dissection or the skin island elevation may be completed after preceding proximal pedicle identification. The skin island should be elevated just above the extensor hood on the proximal phalanx of the index finger, leaving the well-defined paratenon intact. Pedicle dissection, preferably undertaken under (2×–4×) lope magnification, should start with elevation and establishment of thin skin flaps on both sides of the zig-zag/lazy-S incision. Among the visible superficial dorsal veins, the ones that have about the same course with the pedicle should be preserved and incorporated to the pedicle with a cuff of superficial subcutaneous layer. Inclusion of at least one or more superficial dorsal vein in the pedicle will increase venous outflow and help avoid post-operative flap congestion. A terminal branch of dorsal sensory branches of the radial nerve can be found easily and included in the pedicle. Then, dissection continues deep with incision of the fascia on the radial half of the first dorsal interosseous muscle along the pedicle axis. Because, after arising from the radial artery at the origin of the first dorsal interosseous muscle, FDMA and associated vena comitantes are located deep in the first dorsal web space and adherent to the ulnar half of the dorsal surface of the first dorsal interosseous muscle. During the radial to ulnar elevation of the deep muscle fascia across the ulnar half of the muscle, FDMA readily comes into vision. The rest of the pedicle elevation is carried out under direct vision of the pedicle with careful cauterization of the branches running deep into muscle either to supply the muscle or to join with the palmar arch. The periosteum at the dorsal radial edge of the second metacarpal bone represents the deep ulnar limit of the pedicle elevation and the dissection in ulnar direction is stopped when it is reached. Inclusion of a muscle cuff around the FDMA will prevent possible unintentional injuries to the delicate pedicle. The harvested island flap can either be transposed onto the defect directly or transferred through a skin tunnel. The donor site is resurfaced with a skin graft (either full thickness or thick split thickness).

3. Report of the cases 

During the last 3 years (between 2002 and 2005), neurovascular island FDMA flap was used in 14 patients suffering from thumb deformities after burn (Table 1). Ages of the patients ranged from 2 to 34 with an average of 21 and all were adult males in military service with the exception of a 2-year-old girl. The left thumb was involved in eight patients while six patients suffered from deformities involving the right thumb. In five patients, deformities also involved the adjacent thenar area. The time elapsed from injury until reconstruction ranged from 5 months to 17 years. Eight patients were operated on under axillary block anesthesia whereas the remaining six patients required general anesthesia.

Table 1. Patient data: sex, age, deformity and procedures that were performed

	Patient	Sex and age	Cause	Time (year)	Deformity	Procedures
	1	M/21	Scald	12	Thenar contracture with MP joint deformity	Contracture release, MP joint atrodesis, reconstruction with FDMA flap
	2	M/22	Contact to fireplace	16	IP joint flexion contracture	Contracture release, IP joint corrective atrodesis with bone graft and reconstruction with FDMA flap
	3	M/20	Contact to fireplace	7	IP joint flexion contracture and deformity	Contracture release, IP joint corrective atrodesis with bone graft and reconstruction with FDMA flap
	4	M/22	Contact to fireplace	17	IP joint contracture of with ulnar deviation	Contracture release, IP joint atrodesis and reconstruction with FDMA flap
	5	F/2	Contact to fireplace	7 m	Severe thenar contracture with palmar extension	Contracture release and reconstruction of thenar area with FDMA flap and skin graft to palmar area
	6	M/20	Contact to fireplace	13	IP joint flexion contracture	Contracture release, IP joint atrodesis and reconstruction with FDMA flap
	7	M/21	Scald	11	MP joint flexion contracture	Contracture release and reconstruction with FDMA flap
	8	M/23	Contact to fireplace	8	IP joint flexion contracture with severe scar formation on ulnar side	Contracture release, IP joint atrodesis and reconstruction with FDMA flap
	9	M/25	Contact to fireplace	7	IP joint flexion contracture	Contracture release and reconstruction with FDMA flap
	10	M/34	Electric	5 m	MP joint flexion contractures with thenar involvement	Contracture release, IP joint atrodesis and reconstruction with FDMA flap and skin graft to thenar area
	11	M/20	Scald	13	Contracture of thenar area	Contracture release and reconstruction with FDMA flap
	12	M/21	Contact to fireplace	10	Severe flexion contracture of IP joint with fix ulnar deviation	Contracture release, IP joint atrodesis and reconstruction with FDMA flap
	13	M/22	Scald	4	MP joint flexion contractures with thenar involvement	Contracture release and reconstruction with FDMA flap
	14	M/21	Contact to fireplace	6	IP joint contracture with ulnar deviation	Contracture release, IP joint atrodesis and reconstruction with FDMA flap

M, male; m, months; time, the time elapsed after the underlying injury until reconstruction; IP, interphalangeal; MP, metacarpophalangeal.

The patients were placed in the supine position with the upper extremity abducted and placed on the hand table and operations were accomplished under tourniquet. After contracture release, if bone or joint deformities existed, corrective arthorodesis was performed first with closing/opening wedge osteotomies followed by K-wire fixation. In two patients, small bone grafts were required to pack the bone gaps. Depending on the location and the size of skin defect on the thumb or first web space, which appeared after contracture release, an FDMA neurovascular island flap was designed over the proximal phalanx of the index finger, then harvested and transferred on to the defects as described above.

4. Results 

All flaps survived and the early post-operative periods were uneventful. The flap size ranged from 1.5× 2cm to 3× 5.5cm. The patients were followed 7–14 months (mean 9 months). All flaps provided adequate soft tissue cover for the exposed vital structures. In two patients, split-thickness skin grafts were used for replacement of the residual skin defects beyond the bone or joint exposition that was covered by the flap. Associated thenar contracture was reconstructed with release followed by skin grafting in one patient. In 10 patients that required bony correction, adequate bony union was achieved with 5–6 weeks of K-wire stabilization. No donor site complication was encountered with a graft-take of 100%. Post-operatively, all patients were given a physiotherapy regimen for rehabilitation. In the case, in which corrective arthrodesis was performed, physiotherapy was postponed 6–8 weeks until the bony union was confirmed while rehabilitation of the others was instituted earlier following wound healing and graft take, usually at the second week after surgery. The flaps were both elastic and durable enough and have grown well with a favorable tissue match for the thumb. Sensation was almost the same as in the original donor site and the patients were informed about the time-period required for adaptation of the brain to new localization of the flap may take months to years. Donor site morbidity was minimal with an acceptable scar, and tendon gliding under skin graft was sufficient without producing any deficit in the functions of index finger. Late follow-up of the patients revealed that all deformities were successfully treated with satisfactory functional recovery and all patients were satisfied with the results (Fig. 2, Fig. 3).

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Fig. 2. Patient 8. (A) Deformity of the thumb due to the burn. (B) Corrective arthorodesis was also performed. (C) Appearance of the hand immediately after the surgery; the flap cover the ulnar site of the finger and donor area was covered with skin graft. (D) Appearance of the thumb at post-operative 6 months.

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Fig. 3. Patient 4. (A) Burn contracture that causes severe deformity on distal phalanx of the thumb. (B) Post-operative view of the thumb; deformity was corrected with FDMA flap.

Regarding how common we used FDMA flap; all patients that underwent surgical treatment for post-burn contractures between 2002 and 2005 were reviewed retrospectively, revealing that 39 of the 92 patients had hand involvement with thumb deformities. In 14 of 39 contractures (about 36%), the FDMA flap was used for reconstruction.

5. Discussion 

Seldom does one encounter a burned hand deformity resulting from an isolated injury because hand burns usually appear as a component of more extensive body burns [19]. In cases of major burns, focusing on patient's survival as a priority may be suggested to be a justification for ignorance of the prompt and proper care for the hands. Debilitating burned hand deformities eventually ensue and future reconstructive attempts rarely satisfy. Despite this general knowledge, what may be noted in our series is that, the majority of our patients have only isolated hand deformity, being otherwise healthy individuals. In our country, isolated burned hand deformities do not seem to be rare and cannot be justified by life saving concerns of a major burn. Especially, palmar contact with heaters by children often results in small third degree hand burns, which usually manifest as digital contractures after healing. However, it was reported that burn deformities usually could not be prevented, even if everything was done correctly during the acute phase care of the victim [20]. Our hospital is a military hospital and in our country, military service is an obligation for all male citizens when they reach age 20. Because of socioeconomic reasons and with the expectation of treatment for free by the government when they are doing their military service, most of the families from rural area intentionally postponed the treatment of minor burn contractures sustained by their children. All of our patients except one were young males with thumb deformities due to untreated childhood burns to their hands, but were otherwise healthy and thus eligible for military service.

Once the hand deformity occurs, it is a difficult problem for the reconstructive surgeon. Grasp and pinch functions of the hand are severely impaired when the thumb is involved. The contribution of thumb to overall hand function is reported to be 40% [21]. Sensation, adequate length, mobility, stability as well as aesthetics are the well-known goals of a functional thumb reconstruction [22], [23]. Hands also have an important role in body image and a cosmetically abnormal hand will be hidden most of the time, especially for socialized individuals [24].

In most digital contractures, treatment was ignored early during childhood or persisted despite the prompt treatment, and lead to development of severe joint deformities in a growing hand. Late reconstruction of these bony deformities usually necessitates arthrodesis for correction. The same is true for the majority of our patients who are young adults with untreated childhood burns to their hands. That's why; corrective arthrodesis of the IP joints was performed to achieve a thumb in functional position.

In correction of deformities involving the thumb, the first step should be the release of soft tissue contracture. Minor soft-tissue contractures can be corrected with Z-plasties when there is a localized band with surrounding healthy skin. However, release of more complicated contractures discloses a skin defect usually larger than anticipated and sometimes results in exposure of bone and/or neurovascular bundles. Skin grafts may be used for resurfacing unless bone, joint or important anatomic structures are exposed. Otherwise, local or regional flaps and in some cases free flaps are required [10], [11], [12]. Skin-grafting has well-known disadvantages and cannot be applied where underlying bony correction is performed. Availability of unaffected healthy skin adjacent to the finger may limit the use of local flaps such as transposition, rotation, and advancement flaps. Regional flap alternatives from the uninjured parts of the hand may well be the best treatment option depending on the location of the deformity [10]. Different flaps have been proposed for thumb and first web space reconstructions [11], including FDMA flap [15], [16], [17], [18], radial-inervated cross-finger [25], dorsal metacarpal flaps [26], neurovascular island flap (Littler Flap) [27], dorsoulnar flap [28], the first dorsal metacarpal flap [29], palmar-hinged flap [30]. However there are limitations for their use, such as donor site morbidity and inadequate flap size, requiring two stage procedures. The FDMA flap was the advantage of a wide rotation arch, constant and reliable pedicle, minimal donor site morbidity, sensation, and unrestricted hand function with early mobilization [16], [17].

Another point that should be emphasized may be the technical details that should be considered during flap harvest. The loose subcutaneous tissues with the dorsal superficial venous system must be included in the pedicle, and flap transfer to the recipient area must be accomplished without tension otherwise venous outflow may be compromised [16]. Moreover, it was reported that even if the arterial pedicle of the flap was injured, the flap might survive thanks to this exclusively venous pedicle. Care must be taken as dissection approaches the dorsum of the MP joint because in this area of very thin subcutaneous tissue, the delicate arteries are susceptible to injury and decreasing caliber of the vessels may not allow a safe dissection. The incorporation of fascia overlying the first dorsal interosseous muscle to the pedicle is of great importance in order to avoid unintentional injury to the pedicle artey.

An important advantage of this flap is that it provides sensation [16], [17], [18]. The nerve enters the flap lateral to the MP joint and superficial to the extensor apparatus. A sensate thumb is of utmost importance for a functioning hand. Although it was less than the ulnar ring finger, island flaps had respective two-point discrimination of 13–15, 12–15mm, better than the usual acceptable two-point discrimination of 15mm [18]. It was reported that brain adaptation to new sensation pattern takes 2–3 months [18]. Our patients were informed about the sensation pattern that was of the donor site and usually adapted well within 3–4 months. Limited size of the flap, between the PIP joint and MP joint, may be regarded as a restrictive factor for its use for extensive soft tissue defects [31]. Although size between these two joints may vary depending on the length of patient's index finger, in our cases, the largest flap was 3×5.5cm. When the dimensions of the defect exceed the limits of the flap size, coverage of exposed anatomic structures is the priority, and the remaining defect may alternatively be resurfaced with full-thickness skin grafts. Additionally, donor site morbidity may be criticized in terms of both cosmetic and functional concerns with possible restriction of extensor tendon gliding under the skin graft [17]. Sparing the paratenon over the extansor apparatus during flap harvest is important to avoid this complication. On the dorsal aspect of the index finger, well-maturated full thickness skin graft was found to be cosmetically acceptable by all of the patients.

Conclusively, in reconstruction of post-deformities involving the thumb and/or adjacent web and thenar area, FDMA flap is a reliable local neurovascular island flap option, offering a good functional and acceptable cosmetic outcome with sensation, elasticity and durability.