Finger and Hand Soft Tissue Defects

Pulp Skeleton

The skeleton of the pulp, formed by the distal phalanx (or P3), has morphologic characteristics that are only present in humans and do not exist in primates.

The diaphyseal segment has a palmar concavity that corresponds to the convexity of the soft pulp tissue. The P3 ends with the distal tuberosity or phalangeal “tuft” with its characteristic proximal projection ( Fig. 9.1 ).

Apart from the skeletal support, the stability and control of pulp deformability is provided by the fibrous structure of the pulp. Differences in this structure allow one to distinguish between a proximal and a distal pulp. The distal pulp is situated next to the distal interphalangeal (DIP) tuberosity; it is compartmentalized by fibrous septa that originate from the periosteum of the phalangeal tuberosity and insert into the deep dermis. The radial arrangement of fibrous septa ensures the partitioning of this distal pulp into celluloadipose IP joint compartments in the shape of a pyramid.

This type of partitioning provides this pulp segment with stability and resistance to deformation ( Fig. 9.2 ). Resistance to deformability is further enhanced by the transverse arrangement of dermatoglyphics at this level. These are also involved in adhesion in the same way as the grooves of a tire on a wet road ( Fig. 9.3 ). Finally, the last element involved in the stability of this distal pulp is represented by the nail plate itself. Blanching of the nail bed observed when doing pulp-to-pulp pinches demonstrates the effective role of counterpressure played by the nail. This stability of the distal pulp is necessary to perform fine pulp-to-pulp pinches ( Fig. 9.4 ).

The disappearance of the nail by sterilization of the matrix, skeletal shortening with disappearance of the phalangeal tuft or replacement of this distal pulp with improper tissue threaten this distal pulp stability.

The organization of the proximal pulp is different. It no longer has the support given by the nail plate laterally, and its single rigid support is provided by the concave diaphyseal segment of P3. The organization of the celluloadipose IP joint lobules is also different. The radially arranged septae have disappeared, and the lobules adopt a spherical shape here ( Fig. 9.5 ). Whereas stability is the characteristic of the distal pulp, malleability characterizes the proximal pulp. By adapting its shape to that of the grasped object, grip is improved.

Vascularization

An understanding of vascularization of the pulp is essential, whether to perform distal replantations (see Chapter 15 ) or local flaps. The two palmar digital arteries come together in front of the distal phalanx next to the terminal insertion of the deep flexor tendon. This anastomosis is located deep in the plane of the flexor insertion. From this pulp arch several arterioles arranged longitudinally make their way toward the distal end of the finger. One of them may be larger and earn the term of central artery of the pulp. These vessels, often of a size greater than 0.5 mm, may be anastomosed and are therefore used during distal replantation. They can reach the end of the finger and bypass it to anastomose with the branches from a dorsal arch ( Fig. 9.6 ). The existence of such arteriolar axes continuing to the tip of the finger means that there is theoretically no distal limitation to performing a replantation. It is not uncommon to find the existence of convolutions on the course of palmar digital arteries near the digital end in cadaveric dissections after a vascular injection. The unfolding of these convolutions by dissection makes it possible to gain the few millimeters necessary to avoid the use of a graft during a distal replantation (see Chapter 15 ). The venous drainage of the pulp should also be known for flaps or distal replantations. Classically the dorsal venous system is described as predominant in the fingers. Beyond the DIP joint, however, the predominant venous elements meet on the palmar aspect of the finger.

In practice, beyond the proximal nail groove, no dorsal vein can be found with a diameter that allows a vascular microanastomosis. In contrast the palm (or pulp) veins may be used to ensure venous return after distal replantation (see Chapter 15 ).

Innervation

Innervation of the pulp is provided by the divisions of the palmar digital nerves. The nerve divides into these terminal branches at the palmar flexion crease of the DIP joint. These branches are still accessible to microsurgical repair.

Healing by Secondary Intention

Frequently and simply performed, this is the primary method for pulp reconstruction. Its simplicity should not, however, involve therapeutic neglect. This method is reserved for superficial pulp tissue loss. Exposure of the distal phalanx contraindicates the use of this method, and it is unacceptable to greatly shorten the skeleton of an already mutilated finger to make this directed healing possible. As with any wound that develops naturally under the effect of a suitable dressing, granulation from the exposed tissues followed by wound contraction and epithelialization from the edges will successively occur. This therefore results in a gradual migration of the scar area distally toward the free edge of the nail. This progressive retraction of the scar is not the least of the benefits of the method. The initial treatment of this soft tissue defect dedicated to healing by secondary intention includes a necessary debridement and irrigation if the amputation is not clean. This can be carried out only in good conditions using a tourniquet and local anesthesia. The first dressing applied is designed to create the conditions of a “local inflammation” suitable for budding. It is then relayed by a bandage soaked in corticosteroids to stop granulations and allow epithelialization. The dressing is required three times a week, with weekly monitoring by the surgeon. Three to four weeks may be required to achieve healing of extended pulp defects. The dressing will be more and more discreet as healing progresses. The patient is encouraged to actively mobilize his IP joints from the initial days, which is only possible if the dressing is not constraining. A temporary scar hyperesthesia can occur once the healing has happened. However, it usually resolves with simple measures of desensitization (hammering and percussion of the digital end). Carried out in this way, healing by secondary intention achieves remarkable results both aesthetically and functionally at the cost of repeated dressings and treatment requiring several weeks ( Fig. 9.8 ). Indications for directed healing are summarized as follows:

• all cases of amputation in area 1

• certain cases of amputation in area 2 when, in particular, adjacent tissues have sufficient vitality to drive this healing

Skin Grafts

All types of skin graft have been proposed to treat distal finger soft tissue defects. Whatever the nature of the grafted tissue, the disadvantages are numerous, such that in our practice skin grafts are very infrequent.

Full-Thickness Skin Grafts

Full-thickness grafts are, in terms of coverage, the “least bad choice.” Mechanically these grafts do not retract and provide a stable and good-quality surface without nevertheless fully meeting the criteria of malleability and thickness of the pulp. Sensory recovery is superior to that obtained by the thin grafts, without providing the discrimination of sensitive flaps. Full-thickness grafts are more demanding as regards the nature of their recipient bed, which should be perfectly vascularized. Finally, the graft must be closely applied, if necessary by a sewn pledget left in place for 8 days. In the case of partial success, coverage can be completed by healing by secondary intention ( Fig. 9.9 ).

Atasoy Flap

The first description of a triangular flap designed for pulp soft tissue defects was by Tranquilli-Leali. However, it was Atasoy who popularized it.

Figs. 9.10 and 9.11 illustrate the main steps for this type of flap. Some points need to be clarified:

• The flap pivots on a subcutaneous pulp tissue hinge; the vascular supply is ensured from the pulp arch by ascending pulp branches.

• For advancement the deep surface of the flap must be completely released from the periosteum of the underlying phalanx. It is the scalpel that performs this release, making every effort to stay close to bone to avoid injury to the pulp arch itself, which is itself located deeply.

• Laterally, using the tip of the knife, the scalpel should cut the fibrous bands that restrict the mobility of the skin island.

• Advancement is maintained by an intradermal needle transfixing the flap and to the distal phalanx. No suturing of the flap borders into a “V-Y” is desirable; it would compromise the blood supply to the island by a strangulation effect and does not reduce healing time. In the same way, it is not desirable to suture the distal edge of the flap to the free edge of the nail because of the risk of a hook-nail deformity, already induced by skeletal shortening.

Kutler Flap

Proposed by this author in 1937, the principle is similar because it involves the advancement of skin triangles on a hinge of subcutaneous pulp tissue ( Figs. 9.12 and 9.13 ). Here, two lateral triangles are used, which come to meet at the midline. These two triangles are sutured to one another. Again we must avoid any suture of these flaps on the free edge of the nail. In 1976 Segmuller proposed modifying this flap by dissecting the neurovascular pedicle at the base of the tip of the skin triangle, turning it into an island flap. This is a technique we do not use, preferring instead to use a true pulp island when the extent and topography of the defect require it.

The thumb has a slightly larger lateral pulp, and for this reason Kutler flaps should be reserved for amputations of the fingers. One of the indications is represented by the short beveled palmar or low oblique amputations in area 2. The obliqueness of the amputation reduces the effective area of residual proximal pulp and makes it difficult to use an Atasoy flap.

Hueston Flap

Described by this author in 1966, this is an advancement-rotation quadrangular flap marked out by an “L” incision ( Figs. 9.14 and 9.15 ). The longitudinal leg of the L unites the palmar and dorsal skins; the horizontal limb is located in a flexion crease. The flap is based on the vascular pedicle that is on the side of the hinge.

Mobilization requires both an advancement and a rotation. The gain obtained is higher than for small distal flaps (Kutler or Atasoy). Its major drawback is that the dissection sacrifices all of the nerve branches from the neurovascular pedicles on the opposite side of the hinge. The angle of the flap that advances the most, the one that provides actual coverage of the pulp defect, is thus also the one that is least sensitive.

It is therefore crucial during dissection of the flap to preserve the sensation on the more important side of the finger. Therefore for the thumb the longitudinal incision will be drawn from the radial side to best preserve the sensitivity of the ulnar side. The opposite will be done when this flap is used for the index. Such a discussion on the choice of hinge side significantly reduces the use of the Argamaso technique (see Fig. 9.15 ). This author proposed the use of an original commissure-based flap to cover the defect created at the base of the finger by advancement of the flap when this flap is used for the thumb. But this device requires a radial hinge flap, which is not desirable. In summary, the advantages of this type of flap are the amount of available tissue and higher potential for advancement compared with small Kutler- or Atasoy-type flaps. However, the sensory drawbacks already mentioned reduce its use. In our practice the Hueston flap has competition in the homodigital neurovascular island flaps for digits and O'Brien-type plasties for the thumb. The poor distal sensory performance of this flap must be noted. Foucher found a distal sensitivity of 7 mm (static discriminative sensitivity at both points) among 43 Hueston flaps reviewed.

The Hueston flap remains irreplaceable for the median digital segment, as will be described.

Venkataswami and Subramanian Flap

This flap is a transition between the real islands that we will present later and the previously described flaps. Its authors reserve it for distal beveled oblique amputations. Its design is triangular. Using a longitudinal incision, the neurovascular pedicle is dissected until it is completely isolated. In contrast the oblique incision that crosses the palmar surface of the finger is used only to separate the fibrous tissue septa, which tie down the palmar tissue to the underlying flexor sheath. The advancement of the flap will be asymmetric, more significant on the longitudinal side and therefore conducive to the coverage of these beveled oblique amputations. There is only one step between this flap and the true island flaps we will describe ( Fig. 9.16 ).

The two flaps described below are reserved to cover pulp soft tissue defects of the thumb. They both completely isolate the palmar skin of the thumb, removing dorsal branches of the palmar digitals when necessary. This is only possible in the thumb, because that finger has an autonomous dorsal vascular supply. Applied without restriction to the digits, these techniques may cause dorsal skin necrosis. The use of such advancement flaps for palmar defects nevertheless remains possible provided the dorsal-destined vascular elements are spared during dissection. We prefer to avoid this difficulty by performing unipedicle flaps for digits.

Moberg Flap

The principle of this flap consists of completely separating the proximal palmar skin using two midlateral incisions. The palmar skin is dissected off the plane of the flexor sheath, which must be respected. All dorsal-destined branches of the digital arteries must be coagulated and sectioned ( Figs. 9.17 and 9.18 ).

The advancement achieved results exclusively from the flexing of the IP joint. Here again, we prefer to fix the distal part of the flap using an intradermal needle inserted into the distal phalanx so as not to add to the risk of hook-nail deformity. Finally, early splinting using a dynamic extension orthosis is desirable so as not to allow permanent flexion of the IP joint to set in. This flap reconstructs a contoured pulp and good sensitivity. We prefer the more advanced version represented by the O'Brien flap, where advancement is not only achieved by flexion of the IP but also by pedicle dissection.

O'Brien Flap

This flap derives from the previous flap. It is actually a sensitive island bipedicle flap. Dissection isolates the quadrilateral flap from the underlying plane of the flexor sheath. The choice of the proximal limit of the flap is subject to discussion. By making this transverse incision more distal, we have a small flap with a long pedicle, capable of consistent advancement. However, by cutting such “postage-stamp” flaps, we create a soft tissue defect that when grafted will be located in the middle area of the thumb when gripping. We therefore prefer to make this incision more proximal, which will ideally situate it in a crease. Advancement is reduced. Two midlateral incisions are used to dissect the neurovascular bundles on each side. It does not seem desirable to dissect the pedicle proximally beyond the level of the metacarpophalangeal (MCP) joint. Indeed, although the vascular anatomy of the thumb is constant beyond the level of the sesamoid bones, made up of two palmar digital arteries, the origin of these two arteries is highly variable. Changes to the original level of these palmar digital arteries are likely to make a more proximal dissection dangerous. As in any island flap whose axis is a digital palmar pedicle, we must spare the peripedicular fat, which supports venous return. Here, the advancement achieved results not only from the flexion of the IP joint but also the effect of the pedicle dissection. We have no hesitation in any case to immediately cover the donor site resulting from advancement with a thick split skin graft taken from the hypothenar eminence using an Andersen blade. A pledget is not necessary to apply these subtotal thick grafts; in fact it could compromise the vitality of the flap by compressing the pedicles. This type of flap, taking into account the proximal limitations of dissection we have mentioned, makes it possible to easily achieve advancement of around 10 mm ( Figs. 9.19 and 9.20 ).

Unipedicle Homodigital Island Flap

The idea of transposing a sensitive pulp island on its neurovascular pedicle began with Littler and Tubiana. These authors use these sensitive pulp islands in their heterodigital form. It was only much later that the use of homodigital island flaps spread. Joshi was one of the first to propose the use of such homodigital unipedicle pulp islands, but the technique he proposed transferred an island cut in part on the dorsal side of the finger, which was therefore mechanically less suitable for pulp reconstruction and less sensitive. It is preferable, in fact, to circumvent these mechanical and sensory disadvantages by transferring the palmar skin immediately proximal to the loss of substance by barely or not involving the dorsal skin ( Figs. 9.21 and 9.22 ).

From a vascular point of view these flaps are based on the palmar digital arteries. The question of their venous return, however, has long been debated. Several authors including Lucas and Eaton dispute the existence of a network of satellite venae comitantes from the palmar digital arteries. Others recognize the existence of these digital veins without finding a continuous deep venous system as far as the pulp. An anatomic study we conducted showed that this network of venae comitantes was in fact neither continuous nor consistent. In its absence the venous return of such a pulp island is probably jointly provided by the superficial vein network and the adventitial vein network to the vasa vasorum of the digital artery.

Homodigital Island Flap

Several authors have published their results on the use of this type of flap. The choice of the pedicle depends on the topography of the pulp defect but also on anatomic and functional considerations. Brunelli recommends favoring the ulnar side of the index and middle finger and the radial side of the ring and little finger as the donor site. In so doing, the dominant hemipulp of the finger is left intact and the risk of anatomic anomalies (very small size or nonexistent artery) that may be encountered in the radial digital of the index and the ulnar of the little finger variations is avoided (see Figs. 9.21 and 9.22 ).

The outline of the flap depends on the defect to be covered. We generally opt for a simple rectangular outline, although some authors have proposed more complex outlines. If necessary, according to the defect to be covered, the flap may exceed the midline on the palmar surface and the midlateral line to include a dorsal skin fringe.

The incision to dissect the pedicle should be midlateral. The use of a Brünner-type incision carries a higher risk of ischemic pain from the tip of the triangular flaps. Indeed, after dissection the finger is dependent on a single digital artery, the other exclusively feeding the cutaneous island (see Fig. 9.21 ).

The skin island is released from the surface of the flexor sheath. During the dissection of the medial side of the flap, a meticulous hemostasis of the pulp arterial arch should be carried out.

The pedicle dissection is performed step by step, conserving the peripedicular fatty environment that participates in venous return. This dissection can be carried out proximally as far as the commissural level. When the required advancement demands such a proximal dissection, it is preferable to spare the dorsal-destined branch from the palmar digital nerve. Hemostasis throughout this pedicle dissection should be meticulous, electively coagulating all of the vascular branches from the digital artery. In particular, each of the two Edwards anastomotic arches in the vicinity of the distal metaphysis of P1 and P2 must be identified and coagulated. The advancement obtained results from both the pedicle dissection effect and the flexion of the IP joints.

The donor site may be grafted using a split skin graft taken from the hypothenar eminence.

At the release of the tourniquet a hyperemia of the skin island usually sets in as it receives the entire flow of the digital artery. This is transient and regresses within days. It is not unusual to also observe a localized hypersensitivity in the transposed skin island area. This also regresses, sometimes at the cost of desensitization.

A splint is placed on the dressing to limit inadvertent extension of the IP joints. From the 10th postoperative day, it should be replaced by a dynamic extension orthosis to combat flexion of the IP joint, which is still a feared complication. Mobilization in flexion is encouraged from the first postoperative days.

Among the pulp reconstruction techniques using the injured finger itself, this flap is the one with the greatest advancement potential (up to 15 mm). The transposed tissue satisfies the demands of pulp reconstruction both mechanically and sensitively. It is therefore our first choice whenever the defect is too large for the use of small flaps (Atasoy, Kutler). However, two restrictions to its use should be noted. On the one hand it requires the integrity of both palmar digital axes, which is important to check using a digital Allen test; secondly, this flap is unable by itself to carry out resurfacing of very large pulp defects (total or subtotal loss of pulp tissue).

Homodigital Dorsolateral Island Pulp Flap (Joshi and Pho)

This is actually a variant of the preceding flap, from which it differs simply by the site of the cutaneous island. This flap was described for the digits by Joshi then applied to the thumb by Pho. In this type of flap the harvesting goes far beyond the midline to the dorsum. It is therefore the dorsolateral skin that is transferred; advancement is based both on the pedicle dissection and a rotation effect so that the most dorsal part of the flap ends up in the distal position. Given this rotational effect, advancement is easier to obtain and requires less flexion of the IP joints. Furthermore, the addition of the dorsal skin to the surface of the flap gives it a higher maximum dimension and enables it to cover larger pulp defects. A certain number of constraints must be highlighted regarding the use of this flap ( Fig. 9.23 ):

• The dorsal skin is thinner than the proximal pulp and as such is less well suited to pulp reconstruction.

• This island is only useful for pulp reconstruction if there is a sensitive island. For the thumb, however, the presence of dorsal-destined branches from the palmar digital nerves is highly controversial. For Wallace and Coupland this participation of palmar nerves of the thumb in distal dorsal innervation is nonexistent. Pho considers it as constant, representing the anatomic basis of its flap. In five cases he reports two-point discriminations varying between 6 and 9 mm.

In our practice the role of such dorsolateral flaps is limited:

• for digits—in cases of large pulp soft tissue defects and no indication for a more sophisticated procedure;

• for the thumb—for a large loss of palmar skin when there is a contraindication to a pulp transfer.

Pulp Exchange Plasty

This flap is actually a variant of the homodigital pulp island. In the case of soft tissue defects involving a dominant hemipulp of a digit (radial hemipulp of the index and middle finger, ulnar hemipulp of the little finger), it is possible to translate the adjacent hemipulp in the form of a sensitive island. Insofar as it is a translation rather than an advancement, a limited pedicle dissection suffices. The donor site is grafted using a thick or full-thickness skin graft. However, such a reconstruction leads to a tapered digital end lacking in thickness on the donor site. The esthetic result is therefore often also poor. These exchange plasties are only indicated for lateral beveled soft tissue defects of limited size and involving a dominant hemipulp. For more extensive defects the use of a free pulp transfer from the toe may be considered if the patient's age allows for a useful result in terms of sensitivity. In elective surgery, such pulp exchange plasties have been proposed as part of treatment of painful neuroma of palmar digital nerves ( Figs. 9.24 and 9.25 ).

Reverse Homodigital Vascular Island Flaps

The two palmar digital arteries are connected by three constant anastomotic arches as mentioned by most authors. These anastomotic arches allow one of the two arteries to ensure the survival of the entire finger. The use of these anastomotic arches to perform reverse vascular island flaps has been proposed by several authors either in nonsensitive form, or as a “resensitized” flap. Besides the distal pulp arch we have already described (see the paragraph on pulp anatomy), there is a proximal arch located in the vicinity of the neck of the proximal phalanx and a middle arch at the neck of the middle phalanx. Tendon and osteoarticular arterial branches come from these arches. The second arch (middle arch) is responsible for the vascularization of these countercurrent islands.

Resensitized Reverse Skin Island Flaps

For pulp soft tissue defects the flap is designed on the palmar aspect of the proximal phalanx. It is raised off the flexor sheath. A proximal midlateral incision allows dissection of the underlying digital nerve. After identifying the necessary length of digital nerve in the pulp defect, this nerve is cut in the palm, leaving a digital nerve stump surrounded by palmar fatty tissue and therefore theoretically safe from neuromas. The palmar digital artery is itself cut between two ligatures at the proximal edge of the skin island ( Figs. 9.26 and 9.27 ).

The dissection then continues from proximal to distal, isolating the pedicle. As in any digital island the peripedicular fatty tissue that supports venous return is preserved. This dissection stops before reaching the neck of the middle phalanx so as to be sure of conserving the anastomotic arch that feeds the countercurrent flap. The arc of rotation obtained is then enough to bring the flap to the recipient site. A microsurgical suture is performed at this stage between the distal end of the contralateral healthy digital nerve and the flap nerve. The flap itself is sutured with loose stitches, and the P1 donor site is grafted using a full-thickness skin graft.

This flap has several advantages, including that it has an arc of rotation much more distal than that of the direct pedicle island previously described. It is therefore possible to use it to cover more extensive pulp soft tissue defects. The absence of flexion of the IP joints also avoids any postoperative flexion deformity. Use of this flap requires the integrity of the two palmar digital axes, as well as the anastomotic arch system.

This reverse island resensitizes secondarily as a result of nerve regrowth through the microsurgical nerve repair that is performed. Sensation is therefore relatively lower than that obtained by a direct pedicle flap. However, the distance for axonal regrowth is short, which generally allows a useful result. Moreover, this suture protects against any neuroma on the contralateral digital nerve.

Mechanically the palmar tissue from P1 is an acceptable choice for pulp reconstruction—not as good as the pulp proximal to the soft tissue defect but better than the dorsal skin of a dorsolateral island.

The sacrifice of the artery and digital nerve included in the pedicle is the inevitable downside of this type of flap. Such a sacrifice can be justified for a pulp. We will see later that this sacrifice does not appear to be acceptable when this same flap is proposed for the reconstruction of dorsal soft tissue defects. More recently a modification was proposed, aiming to avoid the sacrifice of the palmar digital nerve. Hirase et al. propose harvesting the skin on the dorsal surface of the middle phalanx and resensitizing the flap using the dorsal-destined sensitive branch of the palmar digital nerve, which is preserved during dissection. These authors reported a two-point discrimination of less than 5 mm with this type of technique.

This type of flap is indicated in extensive symmetric (in other words, not conserving the integrity of either of the hemipulps) pulp tissue loss exceeding the advancement capabilities of a direct pedicle flap.

The other option is a toe pulp flap.

From a sensory perspective, both technical solutions have in common nerve regrowth hazards. The scale tips in favor of the reverse islands when it comes to an elderly patient eager for a quick fix in ambulatory care, especially if the finger is without functional preeminence (middle and ring fingers).

Nonsensitive Reverse Vascular Island Flap

This is the simplified version of the same reverse skin island. The nerve is left in situ, and only the artery and its fatty environment is included in the pedicle. The dissection of the pedicle is more difficult because the nerve is left in situ, but enough fat tissue must be conserved in contact with the digital artery to be sure to include a venous return system ( Fig. 9.28 ).

By definition this flap is devoid of any sensory innervation, and its resensitization can only occur by adjacent neurotization. Our pulp reconstruction philosophy initially led us to condemn this flap because of this initial insensitivity. However, several publications seem to confirm that even in this initially insensitive version, adjacent neurotization is able to provide a useful end result, though not as good as the results of resensitized flaps. This prompted us to use this flap in clinical practice. In children at least, our results confirm those in the literature, establishing the return of an authentic discriminative sensitivity in the area of the flap. In adults we reserve this flap for the reconstruction of nondominant pulps.

Dorsoulnar Thumb Flap

The previous flaps are reserved for the pulp cover of the digits. In the thumb the characteristics of dorsal vascularization allow for the dissection of reverse islands without sacrificing the palmar network ( Fig. 9.29 ).

Anatomic Bases.

The anatomic basis and dissection principles of this flap were studied by F. Brunelli. Although the vascular autonomy of the dorsal aspect of the thumb compared to fingers has already been understood, the mode of termination of the dorsal arteries had never been the subject of previous publications (see Fig. 9.28a ). This study shows that three vascular structures are constant in the dorsal thumb:

• an anastomotic dorsal arch of the nail matrix, which is situated an average of 0.7 cm from the proximal nail groove;

• an anastomotic system uniting the dorsal arterial network to the palmar network, located near the neck of the proximal phalanx;

• a “dorsoulnar” arterial axis connected to both of the previous anastomotic systems, located an average of 1.4 cm from the median axis of the dorsal thumb. This line also marks the course of the corresponding sensory branch of the radial nerve.

Surgical Technique, Dissection of Dorsoulnar Flap for Coverage of Thumb Pulp Defects.

The structures mentioned earlier are drawn on the skin. The skin flap itself is designed next to the MCP joint on the dorsoulnar aspect. The dissection is performed retrogradely, first lifting off the skin paddle. On the proximal edge of this skin paddle the sensory branch of the radial nerve is identified and dissected a further distance of 1–2 cm to facilitate subsequent reconnection. During incision of the proximal edge of the flap, Brunelli recommends staying very superficial, conserving the subcutaneous cellular tissue and vascular elements it contains. The dissection continues with the distal dorsolateral incision, destined for dissection of the pedicle. Once again this incision must remain very superficial, simply removing two epidermal flaps. The pedicle is then raised in one piece without trying to see the components. The dissection continues until it arrives at a point of rotation whose site is variable. When necessary (loss of pulp, thumb keeping the integrity of its length), the flap can be supplied only by the anastomotic arch of the matrix. In this case the dissection should stop 1 cm from the proximal nail groove. If a smaller arc of rotation is sufficient (coverage of an amputation stump, shortened thumb), dissection may end at the neck of the proximal phalanx, preserving the integrity of both anastomotic systems. Once this pedicle dissection has been completed, the flap rotates 180 degrees to reach the pulp defect. The distal dorsolateral incision is left to heal by secondary intention. The proximal end of the sensory branch of the radial nerve is anastomosed to the distal end of the radial digital nerve of the thumb ( Fig. 9.30 ).

Results and Indications.

This flap cannot possibly compete with partial pulp transfers from the toe. Its mechanical properties are inferior because the transferred skin is of dorsal origin. Similarly, in sensory terms the donor site depends on the radial nerve, and the local capacity for discrimination is lower than in the pulp region. However, the original advantage of this flap is its arc of rotation, which makes it usable for the cover of pulp soft tissue defects exceeding the capacity of Moberg or O'Brien flaps. It then becomes an alternative to microsurgery when age, site or wishes of the patient contraindicate this type of solution.

Heterodigital Vascular Island Flap

The heterodigital island flaps were the first to be described. The morbidity that is inherent to the donor site and the problems of cortical reorientation have significantly reduced indications. These are somewhat mitigated by the “disconnection-reconnection” technique. Indications remain, however, for the reconstruction of extended pulp defects of the thumb ( Figs. 9.31 and 9.32 ).

The donor site is provided by a functionally less important hemipulp—typically the ulnar hemipulp of the ring finger—but it is also possible to use the ulnar hemipulp of the middle finger in the same way. A digital Allen test will ensure the integrity of both digital axes of the donor finger but also the neighboring finger. The extent of the flap depends mainly on the defect to be covered. The medial limit of the flap is the midline. It is possible to extend beyond the midlateral line, thus recruiting the territory of the dorsal-destined terminal branches of the palmar digital nerve. Proximally the flap may extend to the lateral side of P2 when required. Distally it is important to conserve a few millimeters of the distal pulp to limit morbidity and improve the bed for skin grafting.

The pedicle dissection is performed using a hemi-Brünner or a midlateral approach. The incision continues along a zigzag in the palm, and the pedicle is isolated in one block: artery, nerve and periappendicular fat.

At the juncture of the common neurovascular bundle in the fourth web, the radial digital artery of the little finger is ligated. An intraneural dissection is necessary to separate the fascicles supplying the flap from those supplying the radial hemipulp of the neighboring little finger. After dissection a useful length of 8–10 cm is obtained. To bring the flap in situ in the thumb, we can opt for tunneling or an open transfer so long as any tension or compression of the pedicle is avoided. The donor site requires a full-thickness skin graft.

The disadvantages of this type of flap are related to the morbidity of the donor site and to cortical reorientation problems of the sensitive area thus transplanted.

The morbidity of the donor site arises from mechanical discomfort due to insufficient padding of the donor finger and discomfort related to the insensitivity of half of the finger. The pain due to exposure to the cold is frequent if not constant.

The most serious disadvantage of this flap is the lack of real integration of it in the recipient site, such that tactile sensations remain localized to the donor finger. This illustrates the irreversibility of the cortical orientation. In some cases the influence of proprioceptive stimuli in the recipient finger may result in a better pseudointegration. Such a disability has led to modifying the surgical technique. Conninck proposed performing a secondary section of the transferred digital nerve with reconnection to the corresponding digital recipient. Foucher proposed performing this disconnection-reconnection immediately. The problems of integration are thus resolved at the cost, it is fair to say, of difficulty and the additional technical risk involved in nerve anastomosis. However, the decline in terms of discrimination capability caused by this nerve suture must be put in perspective. Thus Kragi, investigating the long-term outcome of six thumbs resensitized by Littler's flap, found no cases where discrimination is below the threshold of 15 mm.

Given this morbidity inherent in the donor site and the sensory problems encountered, the indications for this type of transfer have become scarce. In a young patient we prefer to repair extensive pulp defects of the thumb when they exceed the capabilities of a homodigital transfer by a partial toe transfer, in which case morbidity is reduced. The only remaining indications for these flaps are the rare cases of extended defects occurring in elderly patients or in those refusing the hospitalization inherent in a microsurgical transfer (see Fig. 9.32 ).

Heterodigital Island Flaps of Dorsal Origin for Pulp Reconstruction

The dorsal surface of the proximal phalanx of the digits is a poor compromise for pulp reconstruction. Mechanically its thickness and malleability are insufficient. At the sensory level, when this skin is removed as a sensitive island, discriminative capacity remains moderate. With regard to the thumb, however, dorsal islands may represent useful “rescue” solutions when the previously mentioned techniques are impractical. Foucher's kite flap and the pedicled dorsal island on the second dorsal intermetacarpal artery may be used in this way. These two flaps will be detailed in the dorsal reconstruction section.

Kite Flap

We have used kite flaps in the following circumstances: extended palmar thumb defect associated with shortening in an elderly patient or when a microsurgical transfer is contraindicated; associated injury to other digits, contraindicating a heterodigital island pulp flap. The harvesting is the same as for a dorsal-destined kite flap. The disconnection-reconnection of the sensory branch of the radial nerve can be recommended to improve the cortical integration of the flap ( Fig. 9.33 ).

Older Techniques for Coverage of Pulp Soft Tissue Defects

Pulp reconstruction using a random pattern–type flap is well known. Whether using the hypothenar flap for the loss of thumb pulp or thenar flaps for the digits, these techniques have multiple disadvantages: insensitive flaps and long immobilization of the recipient finger in flexion. We have therefore totally abandoned them. For similar reasons the cross-finger flap raised on the dorsal surface of the middle phalanx of the index or the middle finger for coverage of pulp defects of the thumb must be rejected. Chase proposed raising a cross-finger flap on the P2 palmar surface of the middle finger, with a dorsal hinge to cover the pulp of the thumb. Like-for-like palmar skin is provided, but resensitization problems remain the same. The only variant of this cross-finger flap providing a suitable compromise is that proposed by Gaul ( Fig. 9.34 ). However, the advantage of this technique is relative because if one opts for this type of donor site, Foucher's kite flap is a better technical choice. The sensory results will be similar, and by using an island, the two surgeries and necessary syndactylization of Gaul's technique will be avoided.

Pulp Free Flap According to Finger Bank Principle

This is removed from a nonreplantable amputated finger (see Chapter 17 ). If the recipient finger is the thumb, the flap should be based on the ulnar pedicle so as to favor the resensitization of the ulnar hemipulp. If possible, the ideal scenario is the reconnection of the two digital nerves. It is essential to ensure the venous return of such a pulp flap using dorsal veins whose caliber offers greater anastomotic security than a palmar vein. To do this a dorsal cutaneous rectangle is taken in one piece with the pulp island. One or two dorsal veins are dissected in the extension of this dorsal cutaneous rectangle and are reconnected at the recipient site ( Fig. 9.35 ).

Pulp Island Flap According to Finger Bank Principle

In rare cases, despite integrity of the neurovascular pedicle, a finger requires immediate amputation. This is the case for some complex traumas of the index finger. The combination of injury to the proximal interphalangeal (PIP) joint, making this joint vulnerable to stiffness, and complex tendon and skin injuries render conservation of this finger not viable in functional terms. Before proceeding to amputation of this finger, the integrity of one of the digital pedicles can lend itself to harvesting a sensitive island flap for a neighboring finger ( Fig. 9.36 ). Here again, it is often the thumb that is the beneficiary of these sensitive finger bank islands.

Anatomic Bases

In the original description of this thenar flap by Tsai, vascularization was provided by the radial artery. It was later shown that this flap could be removed safely on the superficial palmar branch of the radial artery (“radiopalmar” artery). This branch arises from the radial artery in the groove of the pulse around 2 cm proximal to the wrist crease. It then makes its way toward the thenar eminence along an initially superficial course parallel to the thenar skin fold. In the initial part of its course this artery is easily palpable near the distal tubercle of the scaphoid. In all cases it can be found with a Doppler and then followed distally. The artery becomes deep, making its way into the thenar muscles, which it helps to vascularize. It then gives off its skin and muscle terminal branches. There is often a distal anastomotic communication with the superficial palmar network, which is the basis of harvesting reverse pedicle flaps. The sensory innervation of the skin area of the thenar flap involves branches of the radial nerve (thenar branch according to Lejars), the median nerve (palmar cutaneous branch) and the musculocutaneous nerve. Finally, some authors have noted an inconstant perforating branch from the common digital nerve of the second space.

Surgical Technique

The artery is surface marked on the skin, located by palpation and by Doppler. The skin island is outlined, centered on this arterial course, elliptical to facilitate closure. An antebrachial palmar superficial vein that will ensure drainage of the flap must also be marked. The proximal incision is made as far as the radial artery, and the superficial palmar branch is found by dissection at its point of origin. This initial proximal dissection preserves a venous return. The dissection continues distally along the artery in a course that quickly becomes deeper, perforating the thenar fascia. Most often it is necessary to take some superficial fibers from the more superficial thenar muscles in the distal part of the dissection to safely remove the flap. More rarely the artery remains superficial, above the thenar fascia plane, facilitating dissection. The distal anastomotic communication with the palmar network is found in the vicinity of the distal corner of the flap and cut between two ligaclips. At this stage the flap can be isolated in an island on its pedicle elements, and recirculation is tested by releasing the tourniquet. Reconnection occurs on the recipient site, usually using one of the palmar digital arteries of the recipient finger for an end-to-end suture. Reconnection of the vein is carried out on a dorsal vein ( Figs. 9.37 and 9.38 ).

Indications for Partial Toe Transfers for Thumb Pulp Reconstruction

All extensive defects affecting the entire pulp and involving a young patient are indications for a partial toe transfer; they leave no palmar tissue that can be used to create an island flap. We could consider raising this island on P1, but the advancement capabilities would be clearly insufficient. The age limit is established at around 40 years of age, where useful sensibility can be expected.

Apart from these extended thumb-palmar defects that in young subjects are also indications for pulp transfers, the loss of “composite” material is also an indication for reconstruction by customized partial transfer. The combination of a pulp defect, even limited, with bone and nail loss can be an opportunity to perform a composite transfer. If the patient is young and has functional needs requiring such a transfer, the flap is then dissected in a customized way, precisely moving the necessary pulp, bone, nail bed or nail matrix.

Indications for Partial Toe Transfers for Pulp Reconstruction of Fingers

Their place is limited. Only large defects of the index radial hemipulp can justify such an intervention if the patient's age provides hope of proper resensitization.

Terms of Use

The use of a skin graft is possible in emergency situations, provided there is an adequate recipient bed. A loss of superficial tissue simply exposing the subcutaneous fatty tissue is therefore a good indication for skin graft coverage. Similarly it is theoretically possible to protect and cover a digital pedicle exposed over a few millimeters but intact by using a simple graft, or indeed a flexor sheath, which if intact, is normally vascularized. However, if this same digital pedicle has just undergone microsurgical repair, if the flexor sheath is open, and especially if the flexor tendons have been repaired, the use of a graft is not possible and local flap coverage is required.

Types of Graft and Donor Sites

Full-Thickness Skin Graft

If thick split-thickness grafts of hypothenar origin are suitable for small soft tissue defects, it is preferable to use a full-thickness skin graft to resurface a large area corresponding to a functional unit or two adjacent units ( Fig. 9.42 ). This is rarely encountered in emergency situations. The donor site should be smooth and accessible during an operation performed under regional anesthesia—in other words, on the upper limb itself. We have abandoned full-thickness skin grafts at the elbow crease or in the wrist flexion palmar crease owing to the esthetic and sometimes functional sequelae their harvesting causes. Because the inguinal region requires general anesthesia, small surface skin grafts necessary in emergencies are most often removed from the medial surface of the arm ( Fig. 9.43 ).

The donor area is converted into an ellipse at the end of harvesting, and closure is ensured by simple sutures ( Fig. 9.44 ). The graft is carefully defatted before it is applied.

Technique

When the soft tissue defect is extensive and approaching the limits of the cutaneous functional unit, it is better to extend this soft tissue defect to give it the exact dimension of a functional unit. The graft is positioned at separate points. We must highlight that to define the exact dimensions of the graft, we must position the finger to be grafted in maximum extension of the IP joints. In this way we avoid underestimating the size to give to the full-thickness skin graft. This will then be applied to its bed using a pledget.

A splint is used to ensure strict immobility of the finger for the first 10 days ( Fig. 9.45 ).

Hueston Flap

Described in this chapter on pulp reconstruction, the Hueston flap is also very useful for coverage of small palmar soft tissue defects ( Figs. 9.46 and 9.47 ). Its hinge includes one of the two palmar digital pedicles kept in continuity. Sensory considerations are in the background here (insofar as the pulp is itself sensitive), and the choice of the hinge side is a function of the topography of the defect and the existence of a possible associated pedicle injury. The first pedicle encountered during dissection is abandoned in its depth, and it is preferable to move away from the vascular and nervous elements, leaving them covered with subcutaneous cellular tissue. The second pedicle is included in the flap hinge. The donor site is grafted by a skin graft taken from the hypothenar eminence. Finally, it is worth noting that it is quite conceivable, if the localization of the defect requires it, to use this flap as a set-back flap, with the principle and mode of vascularization remaining similar (see Fig. 9.45 ).

Laterodigital Flap

The lateral surface of a finger may serve as a donor site for a transposition flap. The local vascular richness allows for dissection of a long, narrow flap with good reliability. Note that unlike a Hueston flap, the flap thickness does not include the palmar digital pedicle. The survival of such a flap is therefore based only on the richness of the dermal and subdermal plexus. Several authors including Boyes, Bunnel and Colson described the technical principles of this flap. In practice it has mainly been used in the secondary correction of palmar and commissural scars. It has less of a place in emergencies, as we will see. The skin flap is drawn along a major axis superimposed on the midlateral line. It is therefore located on the border between dorsal and palmar skin. Its distal boundary is represented by the distal third of the middle phalanx. Proximally the dorsal incision ends at the basal flexion crease of the finger; the palmar incision can, if required by rotation, go beyond the palm itself by a few millimeters. The dorsal incision exposes the Cleland ligament, which must be incised along the entire length of the flap to allow it to be raised. The flap is then lifted from distal to proximal, leaving the deep digital pedicle, artery and nerve. When the dissection reaches the commissural area, a vein still present at this level should be isolated (which ensures the drainage of the flap) from the commissure to the corresponding intermetacarpal dorsal venous axis. When the dissection is complete, the flap pivots 90 degrees on its proximal skin hinge and becomes capable of filling a proximal defect of the base of the phalanx. The donor site is covered using a thick split skin graft from the hypothenar eminence harvested with an Andersen blade. Before placing this graft, Colson advises breaking the palmar incision by an oblique incision, allowing for the rotation of a small triangular flap ( Fig. 9.48 ).

The unique indication of this flap is in an emergency for traumatic defects of the basal phalanx. The width of the available tissue barely exceeds 10 mm. It is therefore the ideal solution for narrow, proximal and rectangular soft tissue defects.

Vascular Island Flap Based on the Palmar Digital Artery

The use of vascularized skin islands based on the palmar digital artery is discussed in the chapter on pulp reconstruction. The use of an artery and palmar digital nerve therefore appears justified to reconstruct pulp. Several authors have suggested making changes to these neurovascular islands to reduce the morbidity of the donor site and as a consequence extend the indications. It is therefore possible to dissect a skin island that is no longer palmar but dorsal (Büchler ). Making use of the supply of the palmar digital artery in the dorsal vascularization of the digits, Rose proposes a similar modification where the skin island is located on the middle phalanx. Trapezoidal in shape, this island is mixed, made up of half palmar and half dorsal skin. The geometry of these fragments therefore reduces the morbidity of a palmar or pulp flap as performed by dissecting a conventional Littler's flap. Moreover, the pedicle of these “arterial” flaps does not include the palmar digital nerve, which is left in situ, avoiding the troublesome anesthesia of a half finger. Defined thus, these flaps have a pedicle length that allows for their use in heterodigital as well as homodigital form. They can even be used in their reverse form, supplied against the normal arterial flow by the anastomotic arches between the two digital arteries. Finally, their dissection is equally possible on one side or the other of the finger and for any of the digits. Their arc of rotation is large, and their use has been proposed for both the palmar and dorsal surface. However, even modified as such, because this technique involves a deliberate sacrifice of a digital digital artery, we formally reject the use of these flaps as first-line treatment to cover the middle palmar digital segment (and even more so for the dorsal side). A classic cross-finger flap, a flap taken from the dorsum of the hand, always seems preferable to us. There are some rare situations where the neighboring finger is unavailable, where no dorsal flap can be taken, that can justify its use ( Fig. 9.49 ).

Cross-Finger Flap

The use of the dorsal skin of a neighboring finger to cover the middle palmar digital segment by using a temporary pedicle flap is a solution that is still viable ( Figs. 9.50 and 9.51 ).

Technically the flap is quadrangular, and if it is raised as the entire dorsal cutaneous functional unit, the esthetic sequelae will be fewer for the donor finger. It can either be harvested from the proximal or the middle phalanx according to whether there is a need to resurface the proximal or middle phalanx segment of the adjacent finger. It is even possible, if the dimensions of the defect requires it, to harvest this flap over two phalangeal segments. The lateral boundary is the midlateral line opposite the hinge. Proximally and distally the boundaries are those of the functional unit by avoiding (if possible) going beyond the dorsal skin that covers the IP joint spaces. At this level the dorsal skin is thin and has a relative excess length that accommodates flexion and would be dangerous to remove. The flap is cleaved from the underlying plane represented by the peritendon of the extensor apparatus. This plane is richly vascularized and provides a satisfactory bed for the graft. At the proximal and distal edges of the flap, hemostasis by ligation of the veins of the dorsal superficial network should be performed.

Dissection ends once the midlateral line marking the boundary of the hinge is reached. At this point the fascia connecting the skin to the periosteum and the peritendon of the extensor should be incised at the level of the hinge. Once this fascia has been incised, we discern the underlying pedicle, and a substantial gain is achieved in the available width of the flap. The flap then pivots on its hinge and is applied to the recipient site, where it is positioned at separated points. An intermediate-thickness skin graft is removed with a dermatome on the palmar surface of the forearm to cover the donor site. The hypothenar skin is not suited to this recipient site because it is too rigid. The flaps are divided around the 15th day by simple section of the hinge. A judicious design of the flap avoids any tension in the hinge and allows early mobilization of both fingers with a syndactyly dressing. At this cost the stiffness of the donor finger is moderate after separation and is amenable to rehabilitation measures and devices. The hierarchical choice of this flap therefore intervenes before more expensive solutions such as vascularized flaps by the palmar digital artery mentioned earlier.

Dorsal Island Flaps for Coverage of the Middle Palmar Digital Segment

When a Hueston-type or laterodigital local flap is insufficient or cannot be performed, or when because of injury the neighboring finger is unavailable for the dissection of a cross-finger flap, we may consider coverage of the defect by a dorsal island flap. In their direct pedicle or orthograde version that we will present first, these flaps cannot reach beyond the palmar flexion crease level of the PIP joint. Within these limits and strictly within the indications we will specify, these flaps provide a valuable solution for coverage of the palmar aspect. The precise anatomic bases and technical details of these flaps will be described in the chapter on dorsal reconstruction, for which they are primarily intended.

Kite Flap (Foucher)

Intended primarily for dorsal thumb reconstruction, a kite flap can provide a coverage solution for the palmar aspect of this finger. We saw that it was only an “average” solution for pulp reconstruction. On the other hand, it is a very appropriate means of proximal phalanx cover, especially if the pulp beyond has normal sensibility ( Fig. 9.52 ). Tunneling is performed on the dorsal side of the first commissure, which makes it possible to bring the flap up to the level of the palmar plane of the thumb.

Other Dorsal Orthograde Island Flaps for Coverage of Middle Palmar Digital Segment

When the kite flap is not available (eg, in the case of proximal amputation of the index), it is possible to dissect a similar vascularized island based on the second dorsal intermetacarpal artery. The unwinding technique with the extensor apparatus should be used here if we want to have the pedicle length sufficient to reach the palmar plane of the thumb ( Fig. 9.53 ).

Besides the thumb, these same dorsal island flaps can be used to cover the palmar digital segment of the digits. Harvesting can be carried out on the dorsal surface of the adjacent finger.

Apart from the kite flap and the second-space island already mentioned, the third and fourth space are also apt to carry out dorsal island flaps. For these two ulnar spaces (middle and ring), however, local anatomic considerations impose the need to dissect a “short pedicle” flap. There are two factors to consider when determining the arc of rotation of these flaps. The first is the distal boundary of the flap, which on the dorsal surface is represented by the PIP joint extension crease. The second factor is the pedicle's axial twist of 180 degrees and its commissural course, which further limits the useful length. These flaps are therefore not able to resurface the entire extent of the palmar surface of a phalanx. However, they represent a backup solution for the lateral side of P1 and the palmar region of the MCP joint.

Retrograde Island Flaps of Palmar Origin to Cover the Middle Palmar Digital Segment

Pedicled Thenar Flap.

The thenar flap, whose use we have already mentioned in free form to cover a small pulp defect, can also be used in a distally based version to cover proximal palmar soft tissue defects of the thumb, index finger and also the palmar surface of the hand in its ulnar half ( Fig. 9.54 ).

Anatomic Basis.

The anatomic basis of this flap have already been mentioned. In its distally based version the flap makes use of the presence of anastomotic connections between the radiopalmar artery and the branches of the superficial palmar arch.

Surgical Technique.

The course of the artery of supply (radiopalmar artery, superficial branch of the radial artery) is identified using a Doppler and followed in the thenar space. The boundaries of the flap are drawn on the skin in an elliptical shape and in an axis parallel to the thenar crease. The maximum dimensions appear to be of the order of 4–6 cm long with a width approaching 3–4 cm. The distal angle of the flap is located at a point near the course of the superficial palmar arch. The dissection begins by individualizing the proximal arterial pedicle just as if it were for the dissection of a free flap. The pedicle found is isolated on a vessel loop in preparation for the clamping tests that follow. The dissection continues by lifting the flap from proximal to distal according to the same technical steps as for lifting a proximal pedicle flap. We therefore follow the feeding artery along its course, which gradually becomes deeper and intramuscular. However, in this variant intended for distal pedicle dissection, we try to follow this artery over the entire area of the flap as far as its distal angle, preserving all of the digital branches encountered during this dissection, until those that are anastomotically destined are located. Near the distal angle of the flap, it may be wise to preserve a hinge of subcutaneous cellular tissue to improve circulation of the skin island. The decisive step of dissection of this distal island is represented by an inventory of anastomotic communications. Connections can be found with the superficial palmar arch or with the palmar vascular network of the thumb. Sometimes both types of connections can coexist, giving this flap two distinct potential pivot points. Carrying out a clamping test is the technical solution that makes it possible to optimize the use of this flap in its distal pedicle variant. A microsurgical clamp is placed on the feeding artery in the proximal aspect of the flap, and the tourniquet is released to judge the efficiency of the distal anastomoses. It is even possible in the case of a double anastomotic system to selectively test each of the two communication systems. Once this test has been performed successfully, it becomes possible to divide the proximal feeding artery between two ligaclips at the proximal angle of the flap. Conversely, if the clamping tests do not reveal sufficient blood supply to the flap, it is still possible to transform this island flap into a free flap based on its proximal pedicle.

Arc of Rotation.

Given the design of this flap and the location of its pivot point, it is used to resurface the proximal digital segment of the index, the middle finger or the thumb ( Fig. 9.55 ). However, it is difficult to reach the PIP palmar flexion crease of the digits. It is also possible to cover palmar soft tissue defects of the palm with this flap, with, in its ulnar half, the reverse thenar flap then entering into competition for this indication with pedicle flaps taken from the forearm (Chinese or interosseous posterior flap).

Skin

As noted, the dorsal surface of the fingers is covered with thin and mobile skin. Near the joint spaces, PIP joint, DIP joint, and to a lesser degree the MCP joint, there is a relative excess of skin, resulting in a characteristic fold ( Fig. 9.56 ).

This excess skin is absorbed during active flexion movements of the fingers, and we must therefore resist the temptation to use this skin to close dorsal skin soft tissue defects. Similarly, any retractable fibrous scar blocking the dorsum of the fingers is likely to compromise flexion. The boundary of the dorsal skin is represented by the dermal area of insertion of the Cleland ligament. Under the actual cutaneous layers is a layer of subcutaneous tissue that participates in the formation of fat and is scarce in the vicinity of the PIP and DIP joints. We will see that it is difficult to use these areas to perform reverse cross-finger flaps. The peritendon of the extensor apparatus is the second element of the gliding system of the dorsal surface of the fingers. It is richly vascularized and consists of a bed that is sufficient for a dermoepidermal graft.

As on the palmar surface of the fingers, it is crucial to consider the limitations of skin functional units when harvesting a flap or planning an incision. Fig. 9.57 establishes the dorsal surface topography of these functional units.

Skin Vascularization of Dorsal Digital Segment

The thumb and fingers are distinguished by the characteristics of their dorsal vasculature, and we have already seen that the thumb has a vascular autonomy on its dorsal aspect, allowing for bipedicle palmar flaps to be carried out without the risk of dorsal necrosis.

Vascularization of Dorsal Skin of Thumb

Several authors have studied this dorsal vasculature (Braun, Kuhlmann ). The vascular supply to the skin of the dorsal surface of the thumb depends on the arterial branches destined for the dorsal thumb from the radial artery from the first interosseous space. These are either independent branches or a digital branch of the first web space dorsal metacarpal artery. Brunelli, after an anatomic study of 20 cases, showed that regardless of their origin, these dorsal arterial axes (although sometimes very small) reached the distal end of the phalangeal thumb. The existence of transverse anastomoses between these arterial axes, one in the matrix area, the other in the neck of the first phalanx, allowed this author to propose a reverse flow island flap based on the ulnar dorsal digital axis ( Fig. 9.58 ).

Dorsal Vascularization of Fingers

Involvement of the dorsal intermetacarpal system in the dorsal vascularization of the proximal phalanx is constant, provided there is an identifiable dorsal intermetacarpal vascular axis. The first two dorsal interosseous spaces are known for their constant vascular anatomy, although the vessel in this space is itself subject to variations in course, origin or termination ( Fig. 9.59 ).

It is therefore possible with good reliability to dissect island flaps based on these dorsal intermetacarpal axes for each of these two spaces. We have already mentioned and will describe later the kite flap dissected on the first space. Earley and other authors have highlighted the potential clinical use of the second-space metacarpal flap ( Fig. 9.59 ).

The dissection technique of these dorsal islands should take anatomic variations of the vascular axis into account. The distal boundary of the skin island harvested on the dorsal surface of the index and middle fingers is itself the subject of discussion. To ensure reliability, we set this boundary at the extension folds with respect to the PIP joint. Earley reported cases of distal partial necrosis when the outline of the flap exceeds this distal boundary and extends to the dorsal surface of the middle phalanx ( Figs. 9.60 and 9.61 ).

Both ulnar intermetacarpal spaces (ring and little) are, on the other hand, known for the inconstancy and variability of the dorsal metacarpal system arteries. For these two spaces it is therefore not prudent to dissect long pedicle island flaps. However, dissection of flaps on the dorsal surface of the proximal phalanx of the ring and little finger is possible, provided we settle for just a short pedicle. Indeed, by stopping the dissection on a point situated between the corresponding metacarpal heads, the palmar vascular supply is conserved (see Fig. 9.58 ).

These short pedicle metacarpal flaps from the ulnar fingers are also more than sufficient in clinical practice, since they are—above all—intended to cover the adjacent fingers. They cannot claim, like the previous flaps, to reach the thumb column.

Involvement of the palmar digital arterial network in the dorsal vasculature is a finding that has, as we have already mentioned, a number of surgical applications. Beyond the PIP joint the dorsal structures rely only on the palmar digital arteries for their vascularization. Strauch isolated cutaneous branches from the palmar digital arteries according to a constant and repetitive distribution at each of the three phalanges. The origin of this cutaneous branch is located near the middle third of the phalanx considered, before the takeoff of Edwards deep anastomotic arch ( Fig. 9.62 ). The first of these branches is for vascularization of the dorsal skin of the proximal phalanx, and its terminal network merges with that of the corresponding intermetacarpal dorsal artery.

Considering the role of the perforating commissural fibers, Levame and Ottero established that the vasculature digital commissure region was based on the wealth of the arterial branches called perforators at this level. These perforators come from the palmar digital arteries, and at the end of their ascending course anastomose with the terminal network from the dorsal metacarpal artery. We have already underlined the need to take these perforators into account when planning to use a dorsal metacarpal island flap in one of the two ulnar spaces (ring and fifth).

Homodigital Local Flaps

Before considering a heterodigital flap, we should consider seeking a solution that uses the injured finger itself as a donor site.

Advancement or Reverse-Flow Bipedicle Flap

This is a simple solution adapted to a transverse loss of tissue perpendicular to the axis of the finger. These injuries are often accompanied by an underlying injury of the extensor apparatus. It is necessary to resist the temptation to close the skin by taking advantage of the relative excess skin obtained on the finger in extension. Closure is actually achieved at the cost of undue tension in the suture area, apparent in active flexion ( Fig. 9.63 ).

A simple releasing incision parallel to the wound, associated with a raising of the flap superficial to the extensor peritendon, is enough to mobilize a small flap. Even if closure of the donor site is possible by simple directed healing, we prefer, for the patient's comfort, to cover this donor site with a thick split skin graft.