The Dorsal Flap of the First Web

INTRODUCTION

The reversed flow pedicle flap based on the dorso-ulnar collateral artery of the thumb was originally described by Brunelli (1993) who used it in 32 cases. There are no other large clinical series of this flap, and there has only been limited use of dorsal flaps of the first web for the treatment of complex lesions of the thumb and index finger. This is despite many anatomical studies demonstrating that the anatomy of the dorso-ulnar artery of the thumb and the dorso-radial artery of the index finger is constant and predictable (Bertelli and Pagliei, 1994; Bertelli et al., 1992; Brunelli 1993; Brunelli and Gilbert, 2001; Earley, 1986; Foucher and Marin Braun, 1990; Kumar et al., 1996). The dorsal aspect of the first web space is an interesting donor site area and is supplied by the metacarpal vessels which arise from the deep branch of the radial artery.

In this paper, we illustrate the use of this flap as a true vascular island flap to cover soft-tissue defects on the apical and lateral surfaces of the thumb and index finger.

ANATOMY AND DISSECTION OF THE FLAP

The dorsal vascular pattern of the thumb, first web space and index finger is well described (Arria and Gilbert, 1990; Earley, 1986; Pistre et al. 2001; Rivet et al., 1990). We agree with the results of all these studies, although the terminology used in this paper is not the same. According to the Nomina Anatomica 1955 (Lanz and Wachsmuth, 1973), a metacarpal artery must supply two digital rays. Consequently, the vessel arising from the radial artery in the first intermetacarpal web is the first dorsal metacarpal artery as the dorso-radial digital artery of the index finger and the dorso-ulnar artery of the thumb originate from it. Brunelli’s flap is located on the dorso-ulnar aspect of the first metacarpal head and is centred, when raised proximally, on the apex of a vascular “V”, produced by convergence of the dorso-ulnar artery of the thumb and the dorso-radial artery of the index finger (the latter is the “dorsal intermetacarpal artery of first web” described by Foucher and Marin Braun (1990)) (Fig 1). The first dorsal metacarpal artery arises from the radial artery (deep branch) after it crosses the anatomical snuffbox and before it passes between the two heads of the first dorsal interosseous muscle. It gives off a radial branch, the dorso-ulnar collateral artery of the thumb, which runs along the thumb metacarpal either in a suprafascial or a subfascial plane. In a few cases this artery is absent, in which case the dorso-ulnar collateral artery arises from the ulnar digital artery at the level of the head of the thumb metacarpal (Brunelli et al., 1999; Brunelli and Gilbert, 2001; Pistre et al., 2001). In these cases, communications between the dorso-ulnar collateral artery of the thumb and the dorsal subcutaneous network of the first web allows proximal extension of the vascular dorso-ulnar axis of the thumb, i.e. the radial arm of the vascular “V”. The ulnar branch of the first dorsal metacarpal artery, the dorso-radial artery of the index finger, runs along the index metacarpal, usually in a suprafascial plane. It ends as tiny vessels which feed the dorsal subcutaneous layers of the index finger and does not extend beyond the junction of the middle and proximal thirds of the proximal phalanx. The dorsal artery supply of the index finger differs greatly from that of the thumb. This is as there is no independent dorsal vascular axis running along the finger and it is inconsistent, fragmented and dependent on the palmar digital arteries. The proximal segment of the dorsal vascular axis of the index ray, which runs along the index metacarpal however is always present and represents the ulnar arm of the vascular “V”. These vascular axes, originating on the dorsal aspect of the first web space, run along the dorsal surfaces of the thumb and the index metacarpal, respectively. They always have one or more distal connections with the arterial systems on the palmar surface of the digits. These anastomoses are found at the interphalangeal joint level (neck of the proximal phalanx) of the thumb, and at the metacarpophalangeal joint level of the index finger (Brunelli, 1993; Foucher and Marin Braun, 1990; Pistre et al., 2001). These anastamoses represent the pivot points of the vascular pedicle. In the thumb the flap may sometimes have a more distal pedicle, at the level of the proximal nail fold arcade. This vascular anatomy allows the mobilization of a dorsal metacarpal reverse flow skin flap in the first web, with a vascular pedicle running along either the thumb or the index ray. The flap is raised on the dorso-ulnar surface of the first web and may be used to cover dorsal and lateral soft-tissue losses from the thumb, thumb amputation stumps, and, as a “cross-finger” flap, to other finger amputation stumps. The presence of anastomoses between the terminal branches of the first dorsal metacarpal artery allows an increased span of the first web flap. When this flap is raised proximally, a large strip of soft tissue including the underlying fascia must be raised in order to ensure the greatest number of connections between the vascular network of the dorsal web and the distal vascular axes.

CLINICAL MATERIAL

We used the dorsal flap of the first web in 15 patients to treat eight subtotal thumb amputations, two thumb amputations, four lateral and palmar losses of soft tissue and one index finger partial amputation. In all cases, a pain-free resurfacing of the thumb was achieved, with partial sensory restoration in nine patients and a reasonable sensory restoration in three very young patients after a period of neurosensory rehabilitation. There was no partial or total flap necrosis. The donor sites were closed primarily in all but two cases in which a skin graft was used. Illustrative cases are shown in Figs 2–6.

DISCUSSION

The dorsal flap of the first web is, in our experience, a quickly designed and safe pedicle flap. Although it is not an innervated flap, we observed reasonable sensory restoration in children after a period of neurosensory rehabilitation. The donor site scars are not particularly obvious when the defect is closed directly using a local flap rather than a skin graft.

The versatility of the flap for the treatment of partial amputations and lateral soft-tissue loss from the thumb, the choice of one or two pedicles and its minimal donor-site morbidity are its major advantages. In our opinion these benefits make this technique superior to other local flaps such as advancement palmar flaps and micro-vascular palmar flaps. Moreover, the dorsal flap of the first web does not carry the risks of free flap procedures. An interesting application of the flap is as a “cross-finger flap” for the treatment of finger tip amputations. Although the flap may become oedematous postoperatively, this resolves after a few days.

Recent anatomical studies have confirmed the practical use of the vascular pattern of the first web space (Brunelli and Gilbert, 2001; Pistre et al., 2001) and an osteocutaneous application of this flap has been proposed (Pellissier et al., 2001).