Although the anatomy is similar, there are many unique aspects to second toe transplantation that distinguish it from reconstruction with the great toe. The second toe is used more commonly for digital reconstruction of the index, long, ring or small finger, and at least in North America, it is used infrequently for thumb reconstruction. The second toe appearance is more like that of a finger and less like a thumb: there is a small nail, narrow phalanges and presence of two interphalangeal joints. In Asia, the common use of 'Zori' type slippers makes second toe transplantation for thumb reconstruction the preferable procedure in spite of the less appealing aesthetic outcome. Like great toe transplantation, the second toe flap harvest is technically challenging, and requires meticulous dissection technique. It is not a flap for the novice microsurgeon.
Any traumatic injury or congenital absence requires a thorough preoperative evaluation by the microsurgeon. The hand is examined to determine the anatomy of the loss, suppleness of joints and soft tissues and the potential requirements for reconstruction. Vascular inflow, innervation, bony structure and the presence of adequate controlling tendons are assessed. The need for any further soft tissue reconstruction is identified, such as a second skin or fasciocutaneous transplant or even a local flap . If a second toe transplant is felt to be the recontsruction of choice, the surgeon must evaluate the lower extremity completely. This includes a history of previous injury or surgery, and a complete skeletal, vascular and sensorimotor examination. Particular attention should be paid to the pedal pulses. If arterial inflow is thought to be questionable whether by history or physical examination, then an angiographic study of the lower extremity is performed. We however do not routinely perform angiography of the lower extremity because we have found the vessel spasm of the foot to be particularly problematic in angiography. This often leads to results that are of no value, i.e. poor visualization of the small vessels in the foot and to the toes. In healthy individuals with no clear indication for angioraphy, the study does not help the surgeon either plan or perform the surgical procedure.
The second toe is narrow, with a squarish nail, and small distal phalanx. It has three phalanges, in comparison to only two in the thumb.
Toe extension is provided by the extensor digitorum longus and brevis tendons. Flexion is provided by the flexor digitorum longus and brevis tendons, with the longus used for digital reconstruction when attached to the flexor tendons in the hand. The plantar digital nerves provide sensation, and travel volar to the deep transverse metatarsal ligaments (not shown below). The digital nerves are short and often require intraneural dissection from the common digital to gain extra length if required for the transplant. The flap is typically disarticulated at the metatarsophalangeal joint, but it can also be taken distal to or proximal to this level. The second metatarsal can provide support for reconstruction of a defect when metacarpal is missing in the hand.
The second to takes its blood supply from a dorsal or plantar system, which varies by patient. In the dorsal dominant system, the first dorsal metatarsal artery gives rise to the digital artery to the second toe. Venous drainage is provided by the subcutaneous venous plexus of the dorsum of the foot.
In the plantar dominant system, the second toe is supplied by the plantar common digital artery, a branch of the medial plantar system.
The large plexus of veins on the dorsum of the foot can be marked preoperatively with a venous tourniquet about the ankle. The dorsal venous arch has multiple interconnections and drainage via the greater and lesser saphenous systems. The extensive connections and generous size of the proximal vessels allows for a long venous pedicle that can be dissected easily.
The venous system of the toes drains into the dorsal venous arch and the greater and lesser saphenous systems.
Arterial inflow to the second toe is supplied by both the first dorsal metatarsal artery and the first plantar metatarsal artery, one of which is usually dominant. In our experience, approximately 60% of patients have a plantar dominant system. Occasionally, both dorsal and plantar systems are of similar caliber. A strong Doppler signal extending from the dorsalis pedis to the first web space ordinarily means a good dorsal inflow will be present. Both systems communicate via branches that dive between the metatarsals and send arterial inflow into the toes.
In the figure below, the second metatarsal and second toe are revealed from a medial perspective, after the great toe and first metatarsal have been peeled away. Communicating branches between the dorsal and plantar systems are visible, as are the braches to the second toe, and the transected branche to the great toe. This anatomy can be quite variable often with the first dorsal system diving through or deep to the first dorsal interosseous muscle. The muscle may need to be divided or an intramuscular dissection may need to be performed to expose the dominant inflow system.
Blood supply to the second toe is provided by the dorsal or plantar system, with one typically dominant over the other. A common ditigal to the first web space sprouts a branch to the second toe and the great toe.
If plantar dominance requires dissection of the vessel proximally on the plantar aspect, the vessel may be traced to the dorsal pedis if the first dorsal interosseous muscle is divided. Some authors recommend vein grafting to the distal plantar dominant system and avoiding the tedious plantar dissection. The disadvantage of vein grafting include a potential increase in the rate of thrombosis and a smaller caliber artery that is present distally. Our preference is to vein graft.
A well padded tourniquet is placed on the ipsilateral thigh and the patient is prepped and draped in the supine position with the entire foot and lower leg below the knee in the operative field. The major draining veins of the second toe are usually drawn on the dorsum of the foot with a marking pen and the incision is outlined as shown below. It extends from the first web space proximally to a level 2 to 3 centimeters proximal to the metatarsophalangeal joint and then distally into the third web space, forming a triangular skin flap proximal to the toe. An incision is usually made proximal to the apex of this triangle to obtain proximal exposure. Asimilar incision is made on the plantar aspect of the foot.
The incision starts from the first and second web space and extends proximally in a "v" shape over the metatarsophalangeal joint.
The dissection is begun in the first web space to identify the arterial branches to the second and great toes, and then the dominant arterial supply.
The dorsal approach is used to find the digital artery to the second toe and venous system. If dorsal dominant, the plantar incision need only be used to isolate the flexor tendon and nerves. If plantar dominant, the plantar incision is also used to find the artery to the second toe.
If the system is dorsal, the rest of the dissection proceeds with relative ease dorsally, isolating the first dorsal metatarsal artery and the second toe extensor and a major draining vein. If the arterial inflow is plantar dominant, the dorsal dissection can be continued to isolate the extensor tendon and a dorsal vein. The extensor tendon is divided with enough length to coapt it to the extensor in the hand.
The arterial and venous branches to the great toe are ligated. The extons, flexor and the plantar digital nerves are divided. ET: extensor tendon. MT: metatarsal LPDN: lateral plantar digital nerve MPDN: medial plantar digital nerve.
The plantar dissection requires isolating the flexor tendon and nerves, and possibly the artery, depending on the dominance of the inflow. In the plantar fat this can be tedious, and particularly tedious if the vessel wraps medially around the plantar sesamoid bone of the great toe. The flexor tendon is divided with enough length to perform a flexor repair in the hand.The metatarsophalangeal joint is disarticulated and the toe is isolated on a the arterial pedicle and a draining vein. The tourniquet is deflated and the circulation is allowed to return to the toe for the appropriate length of time with regards to total tourniquet time. When the recipient team is ready, the artery and vein are ligated and the toe is taken to the field in the hand.
The donor site is closed by approximating the base of the web of the first and third toes. If closure is too tight, the second metatarsal can be shortened. We prefer not to, unless this metatarsal is needed for the flap. A Penrose or suction drain is sometimes used. An ankle splint is optional.
The foot is kept elevated for the first week and then introduced to a progressive dangling regimen. An ace wrap can provide gentle compression during dangling. Weight bearing is not begun until the donor site is well healed, often not until four to six weeks. During this time crutch use can be difficult because use of the reconstructed hand is limited. In bilateral toe transplants crutches are not used. In these cases special shoes that keep the feet in exaggerated dorsiflexion can be used to limit plantar weight and transfer weight to the heels.
Significant wound complications are rare in the healthy patient. If a vascular complication in the transplanted toe requires systemic patient heparinization, then hemorrhage into the second metatarsal space can cause ecchymosis, flap necrosis and delayed healing. This is treated according to the severity of any wound development. Rehabilitation with dangling and subsequent ambulation are delayed.