Anesthetic Considerations
The anesthesiologist decides on the type of anesthesia in accordance with the patient's wishes. Peripheral nerve blocks are associated with minimal hemodynamic disturbance, and, compared with spinal anesthesia, they are a suitable option for high-risk surgical candidates. Preoperative antibiotics are administered thirty minutes prior to the incision.
Positioning Of The Patient
The patient is placed on a radiolucent table in the supine position. A tourniquet is applied to the thigh as a preventive measure and remains uninflated unless there is major unstoppable bleeding. The ipsilateral buttock is raised slightly to ensure that the foot is in neutral rotation; this positioning facilitates the surgical approach. Fluoroscopic imaging in both the anteroposterior and lateral planes will be unimpeded in a patient with an amputated contralateral extremity, and lowering of the contralateral leg facilitates lateral fluoroscopic imaging in all other patients.
Approach
The malleoli, the sustentaculum tali, and the posterior tibial artery are palpated and marked, and a fish-mouth-shaped incision is outlined (Fig. 1). A multifilament suture or small-diameter plastic tube can be positioned 1 cm anteriorly and distally from the tip of both the lateral and medial malleoli to serve as a guide to create plantar and anterior incisions of about the same length. A small injection needle can be used for temporary fixation of the tubing (Fig. 2). The plantar incision may be slightly longer and can be adjusted at a later phase. The limb is prepared for surgery and is draped below the knee. Any areas of forefoot necrosis are covered with a surgical glove or adhesive strip to minimize contamination of the operative field.
The anterior skin incision starts at the level of the ankle joint and continues to the plantar side. Superficial vessels are ligated or cauterized, and special attention is paid to the great saphenous vein. The superficial anterior fascia and extensor retinaculum are carefully preserved, as they will be essential for wound closure (Figs. 3-A and 3-B). On the plantar side, the incision is deepened to the calcaneus. At this stage, an estimation of the viability of the tissue flaps should be made. Although they do not fully guarantee wound-healing, criteria such as skin-edge bleeding and capillary refill are used.
The anterior incision is carried down to the talus. The extensor digitorum longus, extensor hallucis longus, tibialis anterior, and peroneus tertius tendons are cut; they will be tenodesed to the distal part of the wound in a later phase to create a secure foundation for the anterior part of the skin flap. The anterior tibial artery is ligated and the deep peroneal nerve is cut short and buried. The ligaments of the talonavicular and calcaneocuboid joints are cut, disconnecting the midfoot from the hindfoot.
The talus is completely detached from the calcaneus and from the distal parts of the tibia and fibula; this excision should be performed with great caution. A Kirschner wire is drilled transversely through the talar head to provide the surgeon with a secure grip on this cartilage-covered bone (Fig. 4). First, the interosseous talocalcaneal ligaments are transected, followed by the medial and lateral collateral ligaments. The talus can be peeled out, bit by bit, by carefully alternating the dissection from side to side. This is a critical step in the procedure, since the neurovascular bundle lies on the medial side of the talus. The heel pad is nourished primarily by the posterior tibial neurovascular bundle, consisting of the posterior tibial artery, the tibial nerve, and two veins. Proximally, the bundle is positioned on the medial side of the Achilles tendon. More distally, at the level of the medial malleolus, it lies between the tibialis posterior and flexor digitorum longus tendons medially and the flexor hallucis longus tendon laterally. On the lateral side, a distal branch of the peroneal artery, which lies just posterior to the peroneus longus and peroneus brevis, is located more dorsally. It lies behind the posterior tibiofibular syndesmosis and provides lateral perfusion of the calcaneus.
Excessive plantar flexion of the talus subluxates it anteriorly, giving access to the posterior part of the ankle joint. Exposure at this point is facilitated by elevating and supporting the calf. Further dissection reveals the distal articular surface of the calcaneus, and at this point the talus can be removed safely. At this stage, the surgical wound bed is carefully assessed. Hemostasis is obtained, and the superficial nerves (sural, saphenous, and peroneal) are identified, cut, and allowed to retract into the soft tissues.
Osteotomy of the Distal Part of the Tibia and the Lateral and Medial Malleoli
Figure 5 shows a schematic drawing of the planned osteotomy. Prior to the osteotomy, good exposure of the ankle mortise should be obtained. Subperiosteal dissection is accompanied by careful placement of Hohmann retractors to reduce the risk of iatrogenic injury to the neurovascular bundle during the cuts (Fig. 6). The transverse tibial cut should be just proximal to the subchondral plate, resulting in bleeding, cancellous bone. The bone segment is removed. Both the medial and lateral malleoli should be partially preserved, as this will allow better prosthetic fitting.
Osteotomy of the Calcaneus
The heel pad must remain attached to the weight-bearing part of the calcaneus. Calcaneal dorsiflexion of <70° keeps the heel pad well positioned for axial loading as opposed to the 90° originally advocated by Pirogoff (see Fig. 5) This osteotomy angle also allows for generous excision of the necrotic forefoot and tightens the Achilles tendon. The height of the calcaneal cut should be just distal to the posterior articular surface of the posterior facet, and then it should continue anteriorly to below or inferior to the sustentaculum tali. Two Kirschner wires are used as an axis guide for the osteotomy, and their position should be checked with the fluoroscope (Fig. 7). The height and angle can be easily judged on the fluoroscopic image, and the position of the Kirschner wires can be altered, if deemed necessary. It is important to preserve as much length as possible. The cut is made with an oscillating saw, with the blade placed just superior and parallel to the two Kirschner wires (Fig. 8).
Fixation
The calcaneus is positioned in about 15° of external rotation in relation to the tibia and placed slightly posteriorly to align it with the tibia anteriorly. This facilitates approximation of the skin and subcutaneous tissue. Although the occurrence of nonunion is infrequent when viable osseous structures have been solidly fixed and soft-tissue structures have been adequately positioned, following certain basic principles will further reduce the risk of nonunion. The osteotomy cuts should be flush with one another to achieve as much bone contact as possible. Rotation of the calcaneus tightens the Achilles tendon, which works as a tension band to assist in stabilizing the osteotomy. When both anteroposterior and lateral fluoroscopic images show good apposition of the osteotomy sites, stab incisions are made and two 3.5-mm guide wires are inserted. The crossed wires should extend to the medial and lateral tibial cortices and be positioned in the calcaneus just medial and lateral to the heel pad. Their position should be checked with the fluoroscope and the screw lengths should be measured. Cannulated compression screws are then inserted over the guide wires, tightened into the subcortical tibial bone, and embedded slightly in the calcaneus.
Wound Closure
The stumps of the extensor tendons, the extensor retinaculum, and the ankle joint capsule are sutured with absorbable suture to the plantar fascia at the distal part of the wound. Dead space is obliterated with use of subcutaneous absorbable sutures, and, typically, a suction drain is not used. Skin flaps are approximated with interrupted vertical mattress sutures to allow apposition of the skin edges without inversion4. A sterile compression bandage is applied (Fig. 9).
INDICATIONS:
- Forefoot lesions that are too extensive for reconstruction or nonoperative treatment because of gangrene or infection5-7
CONTRAINDICATIONS:
- Insufficient blood supply to the soft tissue and calcaneal region
- A painful and non-viable heel pad
- Osteomyelitis of the distal part of the tibia or the calcaneus
RELATIVE CONTRAINDICATIONS:
- Uncontrolled diabetes mellitus
- Severe Charcot arthropathy
- Neuropathy
- Smoking
PITFALLS:
- If the wound appears infected intraoperatively, an open-flap amputation may be performed. The wound is only approximated, and secondary wound-healing is allowed to occur. Closure of the healthy granulating wound can be achieved after ten to fourteen days.
- Symptomatic nonunions can cause pain and discomfort. Proper handling of tissues, adequate bone preparation, and rigid fixation can reduce the rate of this complication.
- Improper handling of the transected nerves may lead to the formation of a neuroma.
- The skin flaps should be fashioned properly to allow primary closure of the wound, as achieving primary healing of the wound is extremely important. If the flaps cannot be approximated due to the extent of tissue necrosis or because of an incorrect estimation of the incision level, wound closure can often be achieved by revising the calcaneal and tibial cuts. This will result in greater leg-length discrepancy, but relatively more soft tissue will be available.
- An honest intraoperative assessment of the vitality of the wound edges sometimes necessitates amputation at a higher level.
- In younger patients who have not undergone amputation of the contralateral leg, the avoidance of leg-length discrepancy is more important. If sufficient soft tissue is available, a less extensive osteotomy of the calcaneus is an option. In some patients, we have performed a Z-plasty of the Achilles tendon to allow the calcaneus to dorsiflex more.
- The formation of "dog ears" at the medial and lateral corners of the wound is often inevitable. Attempts to reduce this excess of skin and subcutaneous tissue by resection will narrow the heel flap and thereby compromise its perfusion. Eventually, the skin will shrink and the shape of the stump will improve with the use of reduction bandaging and prosthesis wear.
AUTHOR UPDATE:
Pain with weight-bearing makes cannulated screw removal sometimes necessary. Recently, we have had excellent experience with transtibial proximal-to-distal cannulated screw fixation in arthroscopic arthrodesis of the ankle joint, and we will be exploring the use of this method of screw fixation in the future.