Glabrous Skin Flaps - Clinical Tree

Introduction

The word glabrous is defined as “smooth, having a surface without hairs or projections.” Anatomically, glabrous skin is present on the palms of the hands and volar fingers, as well as the plantar surface of the feet and toes. Replacing glabrous skin on the hand and fingers is best accomplished by microneurovascular transplantation of similar skin from the foot, most often from the great toe. A “pseudo-glabrous” surface can be created with transplantation of muscle and split-thickness skin graft (STSG) for coverage of large palmar defects. This pseudo-glabrous surface is relatively insensate but feels smooth and has the septal qualities of glabrous skin.

For palmar defects, we prefer muscle and STSG to fasciocutaneous flaps. Non-glabrous skin flaps, fasciocutaneous flaps, or venous flow-through flaps give excellent cover but do not have the unique septal support of finger and thumb tips. Certainly, replacing “like with like” is the first choice in reconstructing a surgical wound, but glabrous donor tissue is limited and is reserved for smaller defects. For instance, an entire palm cannot be resurfaced with a glabrous donor site because of the lack of availability. An exception would be an unusual case of “spare parts” surgery, where donor amputated tissue is present that cannot be replanted. Non-glabrous tissues have drawbacks: these flaps do not have the density of nerve fibers, and therefore less chance for fingertip quality reinnervation; they may be hair-bearing; and their color match may be inconsistent.

This chapter focuses on the great toe and second toe pulp neurovascular island flaps and medial plantar instep neurovascular island flaps, which all provide glabrous skin on a consistent vascular pedicle. The toe pulp flap can be used to resurface distal digital pulp wounds, while the instep flap can provide a larger area of tissue approaching the size of an entire volar finger or a comparable-sized palmar defect.

Regional Anatomy (see Fig 13.7 , Fig 13.8 , Fig 13.11 , Fig 13.15 , Fig 13.16 , Fig 13.17 , Fig 13.19 )

Arterial Anatomy of the Region (see Figs 13.15 and 13.17 )

Arterial blood supply to the foot and toes comes from either the posterior tibial or anterior tibial system. The anterior tibial artery becomes the dorsalis pedis artery over the dorsum of the foot under the extensor retinaculum. At the level of the proximal first metatarsal interosseous space, the dorsalis pedis bifurcates, sending the first dorsal metatarsal artery along the dorsal aspect of the interspace between the first and second metatarsal and a second communicating branch that travels deep. This branch perforates the interspace to communicate with the plantar system.

The posterior tibial arterial system enters the foot posterior to the medial malleolus of the tibia in the tarsal tunnel. This artery then bifurcates into medial and lateral plantar arteries, with the medial plantar branch further subdividing into several branches. The lateral plantar branch joins the plantar system at the level of the base of the metatarsal. Multiple common digital arteries branch at this level and travel deep to the metatarsal and eventually join the dorsal metatarsal arterial system just distal to the transverse metatarsal ligament. At this junction, the artery immediately bifurcates, sending terminal digital artery branches both medially and laterally.

At the level of the first cuneiform the medial plantar artery divides into several branches. The medial branches communicate with the dorsalis pedis, while perforators come through the intermuscular septum between the abductor hallucis and flexor digitorum brevis to supply the medial plantar perforator flap.

Venous Anatomy of the Region ( Figs 53.1 and 13.19 )

Small veins over the dorsum of the great and second toe coalesce into tributaries that connect to a venous arch on the dorsum of the foot, the completeness of this arch being variable. These veins run in the subcutaneous system just under the dermis and in the fatty tissue above the deep fascia of the foot, superficial to the extensor tendons. The venous arch drains into the dominant saphenous system. Long venous pedicles on any foot flap can be harvested with the saphenous system for a vein of virtually any length necessary. A second deep venous system of small venae comitantes accompanies the proper digital arteries to the toes but is generally too small for microvascular transplantation. If these veins are traced proximal to the posterior tibial artery or dorsalis pedis artery, they are larger and can sometimes be used for microvascular repair. The subcutaneous veins are, however, much larger and more amenable to microsurgical repair in most cases.

Figure 53.1, Cutaneous nerves and superficial veins of the foot. 1. Great saphenous vein; 2. superficial peroneal nerve; 3. medial dorsal cutaneous nerve; 4. saphenous nerve; 5. intermediate dorsal cutaneous nerve; 6. sural nerve; 7. extensor retinaculum; 8. lesser saphenous vein; 9. dorsal cutaneous nerve to the second web space and dorsum of great toe; 10. dorsal cutaneous nerve to the third web space; 11. dorsomedial cutaneous nerve to the great toe; 12. dorsal cutaneous nerve to the fourth web space; 13. deep peroneal nerve; 14. dorsal venous arch; 15. dorsal metatarsal veins.

The medial plantar perforators are accompanied by venae comitantes and are able to drain the medial plantar flap. These vessels are traced back to a large branch of the medial plantar system to allow for the size necessary for microsurgical repair. Although they are comparable in diameter to the medial plantar artery, the medial plantar comitans vessels are quite thin and more difficult to handle. Another option for venous drainage is to trace a superficial vein back to the saphenous system or a large branch and use this thicker-walled system for venous drainage. Either system is adequate to decompress the arterial inflow.

Nerves in the Region (see Fig 13.7 , Fig 13.8 , Fig 13.11 , Fig 13.15 , Fig 13.16 , Fig 13.19 )

Sensory nerve supply to the plantar aspect of the foot and toes comes from the posterior tibial nerve.

The medial side of the foot is supplied by the medial plantar nerve, one of the branches of the posterior tibial nerve, the other being the lateral plantar nerve. The medial plantar nerve supplies sensation to the great toe, second, third, and medial side of the fourth toe. The plantar digital nerves lie just plantar to the digital arteries.

Branches from the medial plantar nerve or saphenous nerve may course through the medial plantar flap; whereas these nerves are inconsistent in their supply to the flap and we have not generally used them, they can potentially innervate the medial plantar flap.

Great Toe Pulp Flap and Second Toe Pulp Flap

Flap Anatomy

Arterial Supply of the Flap ( Case 1 , Fig. 53.4 , see Figs 13.15 and 13.19 )

The blood supply to the great toe pulp and second toe pulp flaps can be either dorsal or plantar dominant, depending on the patient's anatomy. The dorsal system is dominant in 60% of cases. The dorsal system is technically simpler to dissect than the plantar system, although it can sometimes run deep between the first and second metatarsals, complicating the dissection. The plantar system is slightly more difficult to expose because it lies deeper and plantar foot exposure is more tedious with a patient in supine position.

Dominant:

first dorsal metatarsal artery or plantar metatarsal system

Length: first dorsal metatarsal 3 cm (range 3 cm to very long if traced to the anterior tibial artery); plantar metatarsal 2.5 cm (range 2–3 cm)
Diameter: first dorsal metatarsal 1 mm (range 0.5–3 mm); plantar metatarsal 1 mm (range 0.5–3 mm)

If the first dorsal metatarsal artery is traced to the anterior tibial artery, then the surgeon must be certain that the posterior tibial artery can supply circulation to the foot. This can be done with preoperative angiography or an Allen's test of the foot.

The dorsal and plantar arterial systems join just distal to the transverse metatarsal ligament, in the first web space. At this point, small digital arteries branch laterally and medially. The branch going laterally becomes the medial digital artery of the second toe. The branch going medially at the first web space becomes the lateral digital artery of the great toe.

Minor:

first dorsal metatarsal or plantar metatarsal system

When one system is dominant, the other is considered the minor blood supply.

Venous Drainage of the Flap ( Fig. 53.1 )

Primary:

dorsal venous branches of the great saphenous vein

Length: 3 cm (range 3 cm to as long as the saphenous vein can be traced)
Diameter: 3 mm (range 3–6 mm)

Finding adequate venous drainage for the great toe or second toe neurovascular island flap can be difficult at times. Venous drainage is more prominent over the dorsum of the foot and toes.

Secondary:

venae comitantes of the first dorsal metatarsal artery and proper digital arteries

Length: 3 cm (range 3–5 cm)
Diameter: 0.5 mm (range 0.25–3 mm)

Although extremely small, these veins can be preserved and traced to superficial system branches. The superficial system in continuity with the deep venae comitantes can then be used for microsurgical repair and drainage. These veins can be used as the only drainage system if they are adequate in size for repair and have not been damaged by dissection.

Flap Innervation ( Fig. 53.1 and Fig 13.8 , Fig 13.15 , Fig 13.19 )

Sensory:

the plantar digital nerve of the great toe supplies the toe pulp. The plantar digital nerve of the second toe supplies the second toe.

The plantar nerves lie just plantar to the digital artery. The skin landmark is just plantar to the midaxial line of the toe. When dissecting in the interspace between the great and second toes, the nerve is usually first visualized and the smaller digital artery can be found slightly dorsal to the nerve.

Flap Components

The neurovascular island flap from the pulp of the great toe is a sensory cutaneous flap of glabrous skin. Other components can be added by expanding the flap to include nail, bone, etc. (see Flap modifications, below.)

Advantages

Excellent choice to replace glabrous skin loss of the thumb or fingertips.
If the flap is designed to be no wider than 2 cm, then the donor site can be closed primarily. The donor site may require a skin graft if the harvested flap is larger, thus prolonging patient recovery considerably.

Disadvantages

Harvesting this flap can be technically demanding and inset of the flaps requires microsurgical skills.
The surgeon often needs to harvest a thick flap in order to make sure that the artery is incorporated in the flap dissection. Therefore the flap can often be bulky on the thumb or finger and may require a second operation to debulk it.

Preoperative Preparation

In general, we use the ipsilateral toe as the donor toe as this lines up better when using the ulnar digital artery of the thumb as a recipient artery. If the patient has had a traumatic injury to the foot or toe, then the surgeon should consider using the contralateral toe.

A Doppler examination of the foot and toe will help demonstrate whether the toe arterial supply is plantar or dorsal dominant. We start by identifying the Doppler arterial signal of the dorsalis pedis artery and follow the signal distally. If the signal disappears at the level of the base of the metatarsal, then we can often predict that the toe arterial supply is plantar dominant. If we can hear the signal distal to the base of the metatarsal and the level of the communicating arterial branch, then there will be a usable dorsal arterial system. An arteriogram of the foot is unnecessary in most cases. We use a Doppler examination to assess the dominance of the vascular system. A good signal on either the plantar or dorsal side reassures the surgeon that a viable system will be found on dissection. Arteriography can be predictive but vasospasm in angiography of the lower extremities is often present, limiting visualization. Intra-arterial injection of a dilating agent can be useful. Magnetic resonance angiography is a newer technique, but distal vessels of small caliber can be difficult to assess. Our preference is the pencil Doppler.

Flap Design

Anatomic Landmarks ( Fig. 53.2 and Cases 53.1, 53.2 and 53.3 )

The first metatarsal artery is located between the first and second metatarsal bones.

Figure 53.2, Anatomic landmarks. (A) Medial view. (B) Lateral view. (C) Dorsal view.

Flap Markings and General Thoughts About Flap Design ( Figs 53.4–53.6 )

The flap is designed as an oval with the long axis along the midaxial line of the lateral aspect of the great toe. If the surgeon wishes to use the second toe pulp, creating a bilobed flap, or if the second toe donor is preferable for whatever reason, marking of the oval on the medial second toe can be performed.
To achieve primary closure of the donor site, the flap should not be any wider than 2 cm. If primary closure cannot be completed, a small skin graft can be used, or healing by secondary intention of the areas that have excessive tension on closure is an option.
The oval is usually 3–4 cm long.
The dorsal side of the oval marking should be designed to incorporate enough skin between the lateral nail margin and the incision to get good suture purchase for skin closure. Incision markings should continue proximally from the proximal margin of the oval to the web space and at that level should be extended both dorsally and in a plantar direction to identify dorsal and plantar arteries.
One can base a skin flap over the medial side of the second toe based on the medial digital artery of the second toe or a larger skin flap from the lateral side of the great toe based on the medial digital artery of the great toe. The medial digital artery of the great toe is small and sometimes from a lifetime of walking can be scarred.
Venous drainage of the dorsum of the foot and toe should be marked out preoperatively by having the patient hang the leg over the bed or chair in a dependent position. In this position, indelible ink should be used to mark veins, especially looking for veins draining the lateral side of the great toe.
When the dorsal system is dominant, the dissection is simpler. A longer pedicle can be included with the flap, and a shorter incision is needed on the plantar surface of the foot which diminishes rehabilitation time.

Special Considerations

The oval flap can be used to reconstruct a skin/soft tissue defect in a finger. Taking the flap in combination with nail or in continuity with phalangeal bone can aid in reconstruction of complex composite defects. If a secondary soft tissue defect is present in the hand, this flap can be combined with a dorsalis pedis or even an extensor brevis flap. However, insetting and folding can be difficult and the surgeon must be wary of kinking the vascular pedicles to a chimeric flap.

Flap Dimensions

Skin Island Dimensions

Length: 3 cm (range 1–4 cm), maximum to close primarily: 4 cm
Width: 1.5 cm (range 1–2.5 cm), maximum to close primarily: 2 cm

In order to achieve primary closure, the flap width should not exceed 2 cm. Using the second toe requires that less width be harvested, because primary closure is more difficult.

Patient Positioning

The patient is positioned supine with an arm table for the injured arm and hand. A well-padded tourniquet is placed on the thigh and the upper arm.

Anesthetic Considerations

We prefer general anesthesia since we are generally working in two teams, on both the hand and the foot. A bupivacaine block is performed at the foot and toe after the flap harvest and closure for postoperative pain control. The block is performed by infiltrating adjacent to the superficial and deep peroneal branches on the dorsum, at the proximal plantar wound subcutaneously, and adjacent to the digital nerves. A block can be performed of the median and ulnar nerves at the wrist if necessary, but we are very careful not to inadvertently injure the recipient artery or vein. We have not performed this procedure under regional block.

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