Vascularized Fibula Transplant with Skin Paddle

The reliability of the skin paddle harvested with the fibula flap has been questioned.  Strategies to increase reliability have included harvesting a greater length of paddle and septum and trying to predict the location of septal perforators.  We have found that using perforator flap techniques and tracing transmuscular perforators when no septal vesels are available, greatly increases reliability of this flap and enhances skin perfusion. 

The fibula is a long thin bone that has close proximity to the peroneal artery and venae and can therefore be harvested on a single large pedicle.  The length of the bone, consistent blood supply and relative ease of harvest make this donor one of the most useful when osseous reconstruction is required.  It has become the workhorse for mandible reconstruction and segmental long bone defects in both the upper and lower extremities.    

Anatomy

Surface and Bone Anatomy

The head of the fibula proximally does not take part in the knee joint although it does have an articular surface with the lateral condoyle of the tibia.  Just distal to the head,  the neck is looped by the peroneal nerve.  This close relationship with the nerve is significant because any osteotomy in this area can subject the nerve to injury.  The shaft of the fibula is palpable laterally, but somewhat protected by the lateral compartment.  The shaft has four surfaces, approximating the shape of a square in cross-section.  The distal end of the fibula forms the lateral malleolus where the bone articulates medially with the talus.  Because the fibula is part of the ankle joint, the distal six centimeters of the fibula are preserved to avoid injury to the ankle joint.  The skin island can be marked on an axis slightly posterior to the axis of the bone.  We usually harvest a paddle length close to the entire length of bone we will harvest, to increase the number of perforators and allow for more options to tailor the inset.  A paddle up to 5 centimeters wide can be closed primarily.

Vascular Anatomy

The peroneal artery is closely positioned to the fibula.  The artery arises from the tibioperoneal trunk, distal to the takeoff of the anterior tibial artery (seen in the illustration below perforating the interosseous membrane).  The peroneal artery sends perforators laterally to the skin of the lower leg, sometimes in a septocutaneous fashion via the lateral intermuscular septum, but often with muscular perforators.  The length of the pedicle is usually short, but can be increased substantially by dessecting the peroneal artery and its venae from the fibula and using the distal bone for reconstruction.

Muscle and Cross-Sectional Anatomy

In cross-section below, the interosseous membrane is seen in black spanning from the tibia to the fibula.  The lateral intermuscular septum sparates the lateral compartment muscles from the soleus.  

When harvesting the osteocutaneous flap, the septum is harvested in continuity with the paddle of skin and fascia of the lateral leg.

Fibula Flap Pre-Operative Assessment

Both lower extremities must be evaluated to determine the presence or extent of any disease and to ascertain the pulse status of the patient.  The feet are examined for signs of peripheral vascular disease and the anterior and posterior tibial pulses are palpated.  Because an intact arch can supply retrograde flow to the major vessels of the foot, it can be helpful to put pressure on the anterior tibial artery when detecting the presence of a posterior tibial puse and visa-versa.  This "modified Allen's test" may detect proximal vessel obstruction masked by an intact foot arch.  

The need for preoperative angiography in young, healthy patients with a normal physical examination has been hotly debated.  Our tendency has been to obtain preoperative angiograms as a guide.  Although rare, we have seen lower extremities with a dominant peroneal artery nourishing the foot and distal anterior and posterior vessels, contraindicating sacrifice of the peroneal artery.   MRI or CT angiography can also be used in many circumstances.

Fibula Flap Harvest

The patient is typically placed in the supine position with a bump under the ipsilateral hip to lessen the need for excessive internal rotation of the lower leg.  Alternatively, the lateral decubitus position can be used, with the harvest leg placed up and the patient held in position with a beanbag.  A well padded tourniquet is placed on the thigh and the leg from the knee down is prepped and draped.  The proximal and distal fibula are marked and the axis of the bone is drawn.  

The axis of the skin paddle is drawn at the posterior border of the fibula.  The paddle is outlined a few centimeters below the neck of the fibula and 5 to 5 centimeters above the medial malleolus.  If less skin paddle is needed, a smaller paddle can be drawn, or the skin can  be trimmed after the flap is harvested.

The anterior flap is elevated just above the muscle and deep to the muscular fascia.  The septum is approached by elevating the fascia from anterior to posterior.  Septal perforators can usually be seen from this anterior approach.  If no perforators are visible, muscular perforators near the septum posteriorly must be preserved and harvested in a perforator flap fashion to the posterior tibial vessels to preserve skin paddle viability.  

The skin paddle is raised from the posterior approach noting these muscular perforators.  If adequate septal perforators were present, the muscular perforators are ligated.  Attention is then turned to the fibula bone.

A small cuff of muscle - a millimeter or less - is left attached to the fibular bone as the surgeon proceeds medially from the anterior approach.  Army-navy retractors help provide countertraction as the muscle is peeled away leaving behind the cuff.When the superior and inferior locations of the planned osteotomy are marked, a right angle retractor is is used to to snugly encircle the bone.  The distal 6-7 centimeters if bone are preserved to spare the ankle mortise and the proximal course of the peroneal nerve is marked at the neck of the fibula to spare the nerve.  This usually still leaves behind a significant length of bone that varies in size with the patient height and build.  Ribbon or Homan retractors are used to protect the soft tissue when the osteotomy is made with an oscillating or gigly saw.  

Bone clamps can then be placed at the superior and inferior ends of the flap to help provide anterior and posterior traction on the interosseous membrane.  Once the interosseus membrane is divided, the peroneal artery and the accompanying venae can be seen.  The distal aspect of the artery and veins are ligated and divided, and the flap can then be raised superiorly on the vascular pedicle.  The tourniquet can then be deflated to obtain hemostasis and ensure good blood flow to the foot.

Post-Operative Care

The ankle is splinted in neutral and the patient is allowed to ambulate in a cast shoe at about a week after surgery, usually with an ace wrap to prevent edema.  At all other times the foot is kept elevated.  The donor site can heal slowly if closed under tension or in the elderly patient.  

References

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