First Dorsal Metacarpal Artery Flap
This is a fasciocutaneous flap first described by Holevich in 1963.1 It was modified and used as a neurosensory island flap by Foucher and Braun in 1979.2 It is based on the first dorsal metacarpal artery (FDMA) or its dorsal digital branches. It is innervated by terminal sensory branches of the superficial radial nerve (SRN).
Indications
The FDMA flap is indicated for resurfacing either volar or dorsal defects of the distal thumb as far distal as the interphalangeal (IP) joint.
It can be used to cover the ulnar surface of the dorsum of the hand and the wrist, or the palm up to the third metacarpal.
It is useful for first web space reconstruction following contracture, and it can provide soft-tissue coverage of the index finger up to the level of the proximal phalanx.
There are no specific age restrictions provided that the radial artery is not involved with atheroma. It can be used in both acute trauma and elective reconstruction.
Contraindications
The flap cannot be used with a radial artery injury in the snuffbox.
If the skin overlying the first web space is included in the flap, skin-grafting the donor site defect may lead to a secondary contracture.
Examination/Imaging
A Doppler probe may be used to check the pulse of the radial branch of the FDMA (FDMAr) and the ulnar branch of the FDMA (FDMAu) against the first and second metacarpal arteries.
Relevant Anatomy
The FDMA arises from the radial artery just distal to the extensor pollicis longus tendon, before the artery dives between the two heads of the first dorsal interosseous (FDI) muscle ( Fig. 7.1a,b ).
The FDMA typically measures 1.2 to 1.5 mm in diameter. There is usually more than one accompanying vein.
The artery runs superficial to the FDI fascia and divides into three terminal branches: the FDMAr, the FDMAu, and the intermediate branch.
The FDMAr runs along the thumb metacarpal and becomes or anastomoses with the dorsoulnar artery. The ulnar branch runs along the index metacarpal up to the metacarpophalangeal (MP) joint, giving branches to the periosteum and adjacent extensor tendons. It terminates in a plexus over the dorsal fascia of the index.
The intermediate branch runs toward the first web space and anastomoses with branches from the other two.
The skin flap is based on either the radial or the ulnar branch of the FDMA ( Fig. 7.2 ). A proximally based flap is rotated around the point of origin of the artery at the base of the first dorsal interosseous space. The arc of rotation can reach the palmar or dorsal thumb up to the IP joint, the wrist, and the palm to the third metacarpal.
There are two sources of arterial supply to the dorsum of the digit. The dorsal aspect of the fingers is supplied by the dorsal cutaneous branches of the palmar digital arteries as well as the dorsal digital branches of the dorsal metacarpal artery and the dorsal cutaneous branches of the palmar digital artery. These branches anastomose with each other; hence, an extended flap can be harvested with skin from the dorsal aspect of the proximal and middle phalanges.
The venous drainage is that of the accompanying superficial veins.
The superficial branch of the radial nerve becomes subcutaneous after it leaves the brachioradialis, and then it bifurcates into two major branches 4 cm proximal to the styloid. Both branches pass radially to Lister′s tubercle ( Fig. 7.3 ).
The major palmar branch (SR3) passes over the first dorsal wrist compartment, and then continues distally to become the dorsoradial digital nerve of the thumb.
The major dorsal branch (SR2) also bifurcates into the dorsoulnar branch to the index (SR1), which supplies the adjacent sides of the second web space.
Surgical Technique
Radial-Based Skin Flap
The procedure can be done with loupe magnification, under tourniquet control. Microsurgical instruments are not necessary. Limb exsanguination with an Ace wrap instead of an Esmarch bandage makes it easier to identify the arterial pedicle.
For coverage of the thumb, the flap is drawn over the dorsum of the index ( Fig. 7.4 ).
The patient is positioned supine with the arm abducted and resting on an armboard. The surgeon is seated facing the dorsal hand.
Under tourniquet, the flap is raised from distal to proximal, in the areolar plane over the extensor paratenon.
The skin incision is continued along the radial aspect of the index metacarpal to include a large subcutaneous vein in the pedicle.
The flap is enlarged ulnarly toward the third metacarpal so that the skin extension lies on the first web space, avoiding a first web contracture. Harvesting a proximal tail with the island flap simplifies insetting and avoids the need for tunneling.
At the second metacarpal neck, a large perforator is consistently present and should be ligated.
The entire interosseous fascia over the FDI is included to avoid a meticulous dissection of the pedicle and to avoid raising the flap on a nondominant branch. The subdermal fascia can be quite thin; hence, care is taken to preserve its continuity with the FDI fascia ( Fig. 7.5a–h ).
The fascia is released from the metacarpal until the flap can reach the defect. If the flap is used for first web reconstruction the interosseous fascia is released from both the thumb and index metacarpals.
Inclusion of a small strip of extensor hood along the radial aspect of the extensor hood is recommended to protect the vascular connection from the pedicle to the skin island.
Either the major palmar or the dorsal branch of the SRN is incorporated into the flap.
Flap dimensions extend from the base of the proximal phalanx to the proximal interphalangeal (PIP) extension crease and can be up to 4 × 2 cm. The pedicle can be up to 9 cm in length.
The proximally based flap is rotated around the origin of the FDMA at the base of the first web space. The donor site is skin-grafted.
Pearls
Some of the advantages of this flap are its variable size, stability, and pliability.
It provides innervated skin with no major donor site morbidity.
Its elevation does not sacrifice a major artery.
It can be transferred as a pedicled flap or an island flap. It has also been used as a purely fascial flap and a free flap.
The innervated FDMA flap allows immediate postoperative mobilization and the avoidance of a nerve repair. It restores sensibility, particularly in the older patient, in whom nerve repairs with a pedicle or a free flap yield poorer results than in younger patients.
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