10.2.1 Arterial Network

The arterial supply of the second toe and its joints is provided by branches of the dorsalis pedis artery, which is an extension of the anterior tibial artery. At the proximal end of the first intermetacarpal space, this artery gives off the first dorsal metatarsal artery (DMA1) and the first plantar metatarsal artery (PMA1). The DMA1 runs in the first intermetatarsal space at a variable depth. Several authors have described its anatomical variations. Gilbert ¹ proposed a classification system based on its depth in the first space:

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  Type 1 (66% of cases): the artery runs superficially in the first space, either above the first dorsal interosseous muscle (type 1a) or in the body of this muscle (type 1b);

  
  
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  Type 2 (22% of cases): the artery runs under the first dorsal interosseous muscle deeply in the first space, then becomes superficial in the distal portion of the space by passing above the deep transverse intermetatarsal ligament;

  
  
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  Type 3 (12% of cases): the artery runs in a deep plantar location over its entire course; this plantar form is the most challenging to work with. When it is encountered, and a long pedicle is required, we typically resort to a bypass to obtain a useful pedicle length instead of performing a tedious and risky dissection through a dorsal approach.

When a second toe joint transfer is performed, it is vascularized by the medial (tibial) proper plantar digital artery of the second toe, which feeds a periarticular anastomotic circle at the level of the PIP joint.

While performed less often, transfer of the second metatarsophalangeal (MTP) joint is performed occasionally. The arterial supply is from the dorsal and plantar network of the metatarsal arteries of the first and second intermetatarsal spaces. These two networks supply an anastomotic circle at the level of the second metatarsal neck. During dissection, it is essential to preserve the continuity of the dorsal and plantar networks to preserve as many branches to the joint as possible. In particular, the second plantar metatarsal artery (PMA2) always contributes to MTP vascularization. Thus, the transfer will involve harvesting both the PMA2 and DMA1.

10.2.2 Venous Drainage of Toe Joint Transfers

The dorsal and plantar veins of the toe anastomose in the web space and drain into superficial and deep venous networks. The superficial network, derived from the middle of the venous arch, drains into the greater saphenous vein. The deep network consists of veins associated with the proper plantar digital arteries.

In clinical practice, the superficial venous network is used for the tissue transfer anastamoses. One or two veins are dissected, up to where they emerge from the skin paddle. Throughout the dissection, it is essential to preserve the existing connections between the skin paddle and the underlying joint, as they support the articular venous return. When dissecting the donor site, the surgeon must also keep in mind the very superficial, practically subdermal, location of the return veins, in the vicinity of the web space and beyond, especially during the skin incision and when the flaps are first developed for exposure. If the dissection is too deep, there is a risk of irreparable damage to this venous return network.

10.4.1 Preparation of the Recipient Site

A dorsal approach is used from the base of the proximal phalanx (P1) to the distal third of the middle phalanx (P2). We prefer a straight-line incision over the involved joint. The extensor mechanism is exposed and can be released (tenolysis) where there are existing adhesions. Exposure of the palmar recipient artery is possible through this dorsal approach by reflecting the lateral slip of the extensor tendon. The PIP joint should be excised using two parallel osteotomies, performed with an oscillating saw with continuous saline irrigation to minimize thermal damage. The joint is resected en bloc, including the remnants of the volar plate. In order to reduce the length of the bone graft that will be required to fuse the donor PIP joint, we usually try to harvest the smallest possible transfer. However, in our experience it is not safe to harvest a transfer smaller than 15 mm. Measurements are taken of the ideal transplant length, i.e., the length of the bones and joint, along with the appropriate lengths of blood vessels. It is never appropriate to plan to lengthen the recipient finger during joint reconstruction. After local instillation of lidocaine 1% (to prevent arterial spasm), the site is covered with a moist bandage and the tourniquet released.

10.4.2 Dissection of Transplant (Donor Site)

Via a dorsal approach, a rectangular skin flap is outlined over the PIP joint of the second toe. This flap will be used postoperatively to monitor the transfer and will provide extra skin to facilitate closure of the recipient site. The flap incision is extended proximally via a zigzag incision. Exsanguination prior to tourniquet inflation should be partial, in order to make dissection of the vessels easier. During the dissection we recommend first finding the draining vein in the subdermal layer which is crucial to preserve the venous return of the transfer. The incision is extended distally on the lateral side of the skin paddle. The lateral proper plantar digital pedicle of the toe is located and carefully preserved as it will be the sole nutrient artery for the second toe. Then the medial proper plantar pedicle is located, and the artery meticulously separated from the nerve; the artery and its articular branches will remain in contact with the joint. The lateral plantar digital artery (the one on the peroneal side of the toe) is the only remaining nutrient vessel for the second toe , whereas the medial plantar artery (the one on the tibial side of the toe) is the nutrient vessel for the harvested joint . The extensor mechanism is divided beyond the insertion of the central slip, level with the osteotomy site, and the lateral plantar artery is cut between two clips at the same level. The plantar arcades are located and cut. The distal osteotomy is performed with an oscillating saw and continuous saline irrigation. The bone is lifted up, exposing the flexor tendon sheath, which is incised longitudinally, leaving its deep face next to the transplant and the plantar plate. The extensor tendon is incised at the level of P1 and lifted to expose the second osteotomy site, parallel to the first, isolating a transplant of the desired length. The flexor digitorum brevis tendon is cut while the flexor digitorum longus tendon is left intact. The transplant is thus isolated as an island on its medial arterial pedicle. Dissection of the nutrient artery is continued in a retrograde manner, if possible until the emergence of the proper lateral plantar digital artery of the hallux, which is left intact. At this point, the tourniquet is released to check the bleeding of the distal osteotomy cut and the skin paddle. The flap is finally divided by cutting the veins and arteries after double ligation. A 1.0-mm axial K-wire is inserted across the middle and proximal phalanges of the toe guided by an image intensifier to provide temporary stabilization of the toe.

10.4.3 In Situ Arrangement of Transplant

The tourniquet in the recipient limb is reinflated. The transplant is positioned, and the axial K-wire advanced with a drill until it crosses the DIP joint and is left outside the tip of the finger. At this point, the rotation alignment of the transplant is set. However, this is difficult because the PIP joint is held extended. The proximal end of the transplant is then reduced onto the proximal donor site bone, and the axial K-wire is driven into the base of the proximal phalanx, leaving the MCP free. Two antirotation K-wires are inserted at each osteotomy site. They can be positioned by hand and applied using a back-and-forth motion. The extensor tendons of the recipient finger and the transferred toe are trimmed as needed. An overlapping tendon suture is performed with maximal tension to account for the likely development of a PIP flexion deformity. If the native central slip is long enough it is linked to the transfer with a Pulvertaft weave aiming for maximal extension. The straight arthrodesis and tendon suturing in full extension both contribute to optimizing the final extension of the PIP joint. At this point, the transplant’s feeder artery is slid into its tunnel under the lateral slip of the extensor tendon and anastomosed to a digital artery using a microscope. The first step is end-to-end anastomosis of the artery to the recipient proper palmar digital artery after adventitial stripping, mechanical dilation, heparinization, and recutting as needed. This is performed using interrupted 10–0 nylon sutures. Next, the veins are sutured end-to-end in the same way linking the donor veins to superficial digital or commissural veins. The tourniquet can be released at this point. Refilling of the skin paddle and blood flow in the return vein are evidence of good vascularization of the transplant. The skin is closed using interrupted 5–0 absorbable sutures. There, skin paddle needs to be sutured in loosely to avoid restricting the return flow in the vein. In doubt, a partial thickness skin graft is harvested from the hypothenar eminence harvested and sutured in place. Supportive dressings are applied in an intrinsic positive position including a volar plaster slab and carefully leaving a window over the skin paddle.

10.4.4 Reconstruction of Donor Site

It requires special attention, even if it is performed at the end of the procedure. It is essential to perform a bone graft, even when the piece of resected bone is as small as possible (about 15 mm long in adults). Shortening of the donor site would simplify this step, avoiding bone grafting and a skin flap; however, the resulting toe will be short, ugly, and uncomfortable when wearing shoes. Various sites can be used to harvest the bone graft. One option is to use the bone block removed from the recipient finger—a new harvest site would not be needed. This technique is particularly useful in situations where the transfer occurs in the context of a reversal of PIP fusion. When this is not possible, we prefer using a bicortical bone graft from the iliac crest. Another option is to harvest the graft from the tibial malleolus. The graft is shaped very carefully. In the ideal case, PIP fusion will be done in slight flexion instead of complete extension, in order to optimize function and appearance. The length is chosen to reproduce the initial length of the donor toe, although 1 mm of shortening is acceptable (depending on the initial length of the second toe).

Fixation at the recipient site consists of a combination of an axial K-wire and oblique antirotation K-wires.

Covering this bone graft with a skin flap is essential. It is important not to resort to local skin reconstruction to avoid a cross-toe flap. Given the harvesting of the skin paddle, and the preservation of the toe’s length, this option is never sufficient and risks compromising both the skin’s healing and the survival and incorporation of the underlying bone graft. For many years, we have used a reversed, de-epithelialized cross-toe flap. We now prefer using a cross-toe flag flap harvested from the third toe and tunneled under the web space skin between the second and third toes. This avoids the need to detach the flap on the 15th day. This flap is supplied by the dorsal arterial network and has always been reliable in our practice, even if capillary refill is slow when the tourniquet is released.