Anatomy of the flap and leg compartments
The lower leg is divided into four compartments: anterior, lateral, posterior, and deep.
The anterior compartment is bounded by interosseous membrane posteriorly, anterior intermuscular septum laterally, and tibia medially. It contains three muscles that, from the medial to the lateral ones, are anterior tibialis, long extensor of the fingers, and extensor along the big toe. In the depth of this compartment, between the first two muscles, we find the anterior tibial peduncle, composed of artery, vein, and nerve.
The Lateral compartment is bounded by an anterior intermuscular septum and posterior intermuscular septum both connected with the fibula. Inside the compartment, there are the muscles peroneus brevis and longus, the most superficial.
The deep posterior compartment contains three muscles bounded by interosseous membrane anteriorly, the transverse intermuscular septum posteriorly and tibia and fibula laterally. From anterior to posterior, the muscles are the tibialis posterior, flexor digitorum longus medially, and flexor hallucis laterally. Furthermore, this compartment contains posterior tibial pedicle composed by artery, vein and the tibial nerve. Peroneal vessels lie between posterior tibial muscle and flexor hallucis.
The posterior compartment includes the soleus, gastrocnemius and plantaris muscles.
13.1.2 Artery and Venous System
The vascular system of the lower extremity begins when popliteal artery gives three main branches: anterior and posterior tibialis arteries and peroneal artery.
The most common branching pattern is with tibialis anterior artery arising first followed by the tibial-peroneal trunk, which then gives rise to the posterior tibial artery and peroneal artery. The peroneal artery origins, normally, 2.5 cm under the inferior margin of popliteal muscle and lies into fibrous canal between posterior tibial muscle and flexor hallucis muscle or, less commonly, inside this muscle. In the distal tract near the tibiofibular junction, the artery gives the terminal malleolar and calcanear branches. The mean arterial caliber ranges from 1.5 to 2.5 mm, while the venous caliber from 2 to 3 mm.
The length of the pedicle is approximately 6 cm but can be increased significantly according to the flap design.
13.1.3 Nerves
The motor innervation derives from common peroneal nerve that surrounds the back and outer side of the neck of the fibula between the two heads of the peroneus longus muscle as well as 4–8 cm below the head of the fibula. It divides into the superficial and deep peroneal nerves. The superficial peroneal nerve descends between the extensor digitorum longus and peroneal muscles and supplies the peroneus longus and peroneus brevis muscles.
The deep peroneal nerve passes obliquely forward and downward around the fibular neck between the peroneus longus and the extensor digitorum longus muscles to the front of the interosseous membrane. It descends lateral to the tibialis anterior muscle and is a medial relation first to the extensor digitorum longus muscle and then to the extensor hallucis longus muscle, the tendon of which crosses the nerve obliquely above the ankle. In its downward course, the nerve first lies lateral to the anterior tibial vessels, then anterior to them, and finally lateral to them again in front of the lower end of the tibia and ankle. This nerve supplies the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius muscles. Injury to the common peroneal nerve leaves the patient with an equinovarus deformity and anesthesia along the anterior and lateral sides of the leg and dorsum of the foot. The sensory innervation is supplied by the lateral branch of the sural cutaneous nerve that can be harvested to provide a sensate skin paddle.
13.2 Analytical Factors and Technical Considerations
13.2.1 Vascular Anomalies
The possible variations of the vascular supply
Congenital anomaly or acquired disease of the trifurcation vessels is estimated to result in a dominant peroneal artery in 7–12% of the population. An uncommon but important anatomic variant is the arteria peronea magna (type III-C by Kim), a congenital anomaly in which the peroneal artery is the sole vessel to the foot, with patients having normal distal pulses and the absence of associated symptomatology. This condition has been described as occurring in 0.2–0.9% of the population [2].
In case of peronea magna or in a congenitally hypoplastic peroneal artery, fibula flap cannot be harvested in this side. Consider harvesting the controlateral side if no anatomical anomalies are present or evaluate a different flap [3].
13.2.2 Donor Site Selection
Fibula flap can be composed of only the bone component or osteofasciocutaneous.
Select donor site based on oromandibular defect and localization of the pedicle in the neck
13.2.3 Flap Harvesting
13.2.3.1 Preoperative Management
It is essential to know if in the anamnesis the patient has vascular problems or previous traumatic fracture of the selected limb.
Pulsation of the posterior tibial artery, the peroneal artery, and the dorsalis pedis must be checked. An Allen test can be performed between dorsalis pedis and the posterior tibial arteries. Nowadays, CT angiography or MRI angiography is mandatory to detect vascular anatomy and anomalies that preclude blood supply in the foot after peroneal artery harvesting.
13.2.3.2 Patient Positioning
The leg should be positioned flexed at an angle between 45° and 90° and the foot resting on a sandbag or similar in order to ensure a stable support.
Preoperative setting and doppler
13.2.3.3 Flap Design
Preoperative setting and tourniqut inflation
The incision line should ideally travel the posterior intermuscular septum, starting 6–8 cm below the head of the fibula, to preserve the superficial peroneal nerve, and reaching 6 cm from the lateral malleolus to preserve the ankle and the knee stability. The skin paddle should be designed including cutaneous perforators previously highlighted with the Doppler. Its ideal shape is elliptical to favor closure by the first intention. Usually, a skin paddle up to 4 cm width can be closed primarily.
Use of the tourniquet is advisable to obtain a surgical field without bleeding during the dissection. An orthopedic cotton bandage proximally wraps leg to avoid the prolonged contact with the inflated tourniquet.
The cuff is secured around the limb proximal to the operative site. Pressure is exerted on the circumference of the leg by means of compressed gas, which is introduced by a microprocessor-controlled source, via connection tubing. When sufficient pressure is exerted, vessels and arteries beneath the cuff become temporarily occluded, preventing blood flow to pass the cuff. While the cuff is inflated, the tourniquet system automatically monitors and maintains the pressure chosen by the user (approximately 350 mmHg). Cuff pressure and inflation time are displayed, and an audiovisual alarm alert informs the user to alarm conditions, such as a cuff leak.
Pneumatic surgical tourniquet prevents blood flow to the low leg and enables the surgeon to work in a bloodless operative field. This allows flap harvesting to be performed with improved precision, safety, and speed.
Before the tourniquet inflation, moderate exsanguination of the limb is also recommended. An Eismarch bandage (a narrow elastic bandage 5–10 cm wide) is used to drain venous blood away from the leg (exsanguinate) before inflating the tourniquet. It is advisable a moderate exsanguination in order to permit the identification of septo-cutaneous perforator pedicles.
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