Reverse Homodigital Dorsal Thumb Flaps
The arterial supply of the thumb is quite different from that of the fingers. The direct or reverse-flow volar island flaps that have been described for the fingers, which are centered on only one arterial pedicle, are not possible for the thumb. Through their anatomical studies, Brunelli and coworkers discovered a consistent artery along the dorsoulnar aspect of the thumb that they used as the basis for a reverse-pedicled skin flap. The flap can be innervated by incorporating the terminal branches of the superficial radial nerve, and it can be used for coverage of distal thumb defects.1
The same authors simultaneously described a pedicled flap based on the dorsoradial artery. The flaps provide satisfactory texture for resurfacing the prehensile surfaces, and they are homodigital, which allows immediate thumb motion. Because of the distal nature of its pedicle, the flap can easily reach the tip of the thumb. Primary closure of the donor site is possible for smaller flaps.
Dorsal thumb flaps are indicated for reconstruction of extensive traumatic loss of the thumb pulp or following tumor excision.
They can be used for coverage of amputation stumps at the interphalangeal (IP) joint level or for coverage of dorsal skin loss over the proximal and distal phalanx.
Innervated flaps can be used to resurface posttraumatic painful neuromas at the thumb tip.
There is no specific age range nor time limit. This procedure can be used for acute and chronic soft-tissue reconstruction.
The flaps cannot be used with injury to the radial artery in the snuffbox, the princeps pollicis, or the radial or ulnar digital artery.
They are also contraindicated when there is a significant soft-tissue injury at the base of the thumb.
The course of the dorsoulnar or dorsoradial artery of the thumb should be identified preoperatively by Doppler and marked on the skin.
Identify and mark the expected pivot point of the flap.
There is a constant dorsoulnar artery, which originates from the palmar arteries at the neck of the thumb metacarpal and runs along the dorsoulnar side of the thumb. It may be as large as 0.1 mm and travels superficially within the subcutaneous tissue, above the aponeurosis ( Fig. 2.1 ).
The dorsoulnar artery is reinforced by an anastomosis with the palmar digital artery at the neck of the proximal phalanx, ~ 2.3 cm from the nail fold.
The artery terminates in a dorsal arcade within 0.7 mm of the nail.
Venae comitantes can be present when there is a larger artery (~ 50% of cases). In the remaining cases, venous drainage is mostly based on tiny venules in the perivascular fatty tissue.
The terminal sensory branch of the superficial radial nerve is located 1 to 2 cm from the medial axis of the thumb.
Moschella and coworkers2 identified a constant dorsoradial artery that arises from the radial artery at the level of the anatomic snuffbox and passes palmar to the extensor pollicis brevis tendon. It then travels subcutaneously along the radial side of the thumb adjacent to a superficial radial nerve branch and remains at an average distance of ~ 1 cm from the medial axis.
This artery consistently communicates with the palmar vessels near the middle third of the proximal phalanx.
The dorsoradial artery communicated with the nail matrix arcade of vessels in only 4/25 cadaver dissections;2 hence a reversed-flow flap cannot be pedicled past the middle portion of the proximal phalanx.
Dorsoulnar Thumb Flap
The flap can be pedicled distally at two levels, which determines the arc of rotation. It can be pedicled at the dorsal nail fold arcade for cases of distal amputation, or for loss of palmar or dorsal tissue. Dissection of the pedicle must be limited to 1 cm from the nail base.
When used for more proximal amputation stumps, it is pedicled on the palmar anastomosis at the neck of the proximal phalanx. In this case, the dissection should be limited to 2.5 cm from the nail base ( Fig. 2.2 ).
The following points are first marked on the skin: (1) the dorsal arcade of the proximal nail fold, 0.9 cm proximal to the nail base; (2) the palmar anastomosis at the level of the neck of the proximal phalanx, 2.5 cm proximally; (3) the course of the dorsoulnar artery, 1 cm from the median axis of the thumb at the level of the neck of the proximal phalanx ( Fig. 2.3a–j ).
The flap dimensions are then marked out on the dorsoulnar aspect of the metacarpophalangeal (MP) joint, centered over the dorsoulnar artery. The skin island should be designed slightly larger than the defect and tailored to the defect shape. A cutaneous tail should be added to avoid tunneling of the flap and to facilitate skin–skin closure after rotation of the flap into the defect.
The flap is raised in a proximal-to-distal direction. The terminal sensory branch of the radial nerve is located and divided 2 cm from the proximal flap edge for flap innervation if desired.
A midlateral incision is then extended along the ulnar side of the thumb connecting to the distal area of soft-tissue loss. This incision is very superficial to avoid damaging the arterial pedicle.
Two dermoepidermis skin flaps are raised in a dorsal and palmar direction starting from the ulnar incision, taking care not to harm the subcutaneous tissue.
An adipofascial extension of the proximal flap allows primary closure of the donor site and avoids tightness of the first web and reduced MP joint motion.5
Apply a split-thickness graft to the pedicle and the adipofascial extension to avoid vascular compromise.
Use the pedicle itself to cover the defect.
Use Coban tape (BSN Medical Inc., Charlotte, NC) for 2 to 3 months after the first week to decrease flap bulkiness.
Raise the flap with a wide strip of subcutaneous tissue because of the venous drainage and random pattern.
Raising the flap with a wide base near the pivot point protects the anastomosis with the palmar vessels and avoids kinking of the pedicle.
The donor site can be closed primarily with flaps up to 4 × 3 cm. In contrast to the dorsoulnar flap, hair growth is rare on the radial side of the thumb.
There is no risk of a first web contracture from harvesting the skin flap.