|
 Great toe transplantation has proven itself to be
the ideal form of thumb reconstruction in cases of traumatic thumb loss and in
selected cases of congenital absence of the thumb. The procedure is, however,
extremely technically demanding, requiring the utmost of skill from the
microsurgeon and microsurgical team. The harvest of the great toe and the inset
on the hand can be both challenging and beset by technical hurdles.
Postoperative monitoring in an appropriate microsurgical unit is essential to
averting potential thrombosis and treating circulatory complications. Accurate monitoring
and early treatment of complications help to achieve a favorable outcome.
Preoperative Assessment
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 great 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.
Anatomy
The great toe has a single interphalangeal joint
like the thumb, and in most patients the total length of the great toe is
comparable to that of the thumb. However, the transverse diameter and bulk
of the toe are greater (many authors believe there is some atrophy after
transplantation). Toe extension is provided by the extensor hallucis
longus and brevis tendons. The longus is typically repaired to the
extensor pollicis longus of the thumb. Flexion is provided by the flexor
hallicus longus and brevis muscles, with the longus used for thumb
reconstruction when attached to the flexor pollicus longus . The plantar digital nerves
provide sensation, and travel volar to the deep transverse
metatarsal ligament (not shown below). The lateral digital nerve is short
and often required 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 this level. More distally, great caution must be taken not
to injure the small digital vessel supplying arterial inflow.
Venous Anatomy
The large plexus of vein 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. This system allows a long pedicle for the
venous system that can be easily dissected free.
Vascular Anatomy
Arterial infow to the great toe is supplied by the 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 toe.
In the figure below, the second metatarsal and second toe are revealed from a
medial perspective, after the great toe and first metatarsal (above in gray)
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 branches 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.
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.
Dissection
The major draining veins of the great toe are
usually drawn on the dorsum of the foot with a marking pen and the incision is outlined as shown
below. The incision extends into the first web space and laterally to a
level just distal the the metatarsophalangeal joint. Medially, the surgeon
should consider a design that
leaves sufficient flap length to enable closure of the wound with minimal, if any,
shortening of the first metatarsal.
Attention is turned first to the first web
space where the dissection proceeds to identify the arterial branches to
the great and second toes, and then more proximally the dominant arterial supply. If the
system is dorsal, the bulk of the rest of the dissection proceeds with relative ease
dorsally, isolating the first dorsal metatarsal artery and the great 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 plantar dissection will then not only require
the usual exposure of the flexor tendon and nerves, but will also entail dissection of the
plantar digital artery to the great and second toes. 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.
Once the plantar digital nerves and flexor tendon are dissected free and
transected, attention can be turned to the joint capsule. The metatarsophalangeal joint is disarticulated while protecting the pedicle and
draining vein.
When the recipient team is ready, the dominant artery and vein are ligated and
transected.
The would is closed without tension to avoid necrosis of the medial flap.
Post-Operative Care
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 donor site 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.
|
