Vascularised Fibular Transfer
The fibula derives its blood supply from branches of the anterior tibial and the peroneal vessels, but when it is transferred as a vascularised bone graft, the peroneal vessels are the sole perfusion source. The peroneal artery is described as a branch of the posterior tibial artery, arising just below the divi-sion of the popliteal into the anterior and posterior tibial branches, but different arterial patterns exist, and when a fibular transfer is being considered it is essential to carry out preoperative arteriograms, anomalies and arteriosclerosis providing the two main contraindications to its use.
The peroneal vessels run distally alongside the fibula, behind the interosseous membrane. In the upper half of the bone they are separated from the interosseous membrane by tibialis posterior, which there is tak-ing origin from it, but in its lower half they lie directly behind the membrane. They provide the nutrient artery which enters the fibula a little above its mid-point, and also have branches which reach the surface of the bone.
Septocutan-eous perforators from the peroneal vessels also pass laterally behind the fibula in the intermuscu-lar septum between the peroneal muscles and soleus, and perfuse the overlying skin. These allow the fibula to be transferred as an osteocutaneous free flap, as well as a vascularised bone graft.
The length of bone which can be harvested
extends from just below the head to above the lower tibiofibular joint, approximately 30 cm, and its segmental pattern of blood supply allows osteotomy to be carried out. The perforating branches are capable of supporting a skin island up to 10cm x 20cm.
Despite the loss of the shaft of the bone, the leg functions remarkably normally in the adult.
In children and adolescents, where long bone growth is not complete, greater circumspection is required in its use, because of the risk of tibial bowing. Raising the flap
The procedure is carried out under tourniquet, and the line joining the head of the fibula and the lateral malleolus is marked out on the skin.
When the transfer is of bone alone, a proximodis-
tal skin incision is made along the fibular skin marking, over a length to match that of the bone to be harvested, and the skin flaps are raised on each side to allow the septum which separates the posterior and peroneal muscle compartments to be identified. As a first step, the common peroneal nerve is identified, and care is taken to protect it.
It represents the proximal limit of har-vesting the bone, the ankle joint being the distal limit. The muscles on each side of the septum are separated from one another, and the lateral sur-face of the fibula reached.
When a skin island is being transferred with the
bone as a composite, it is outlined on the skin as an oval placed symmetrically over the septum between soleus and peroneus longus, centred over the middle or the middle and lower third of the fibula. The skin incision is made, and extended
proximally and distally as necessary, and the flap is elevated from its anterior and posterior borders, deep to the investing layer of fascia, as far as the intermuscular septum.
The septum contains perforating vessels, branches of the per-oneal vessels, which provide the perfusion source for the skin island, but some of the vessels pass into the muscles on each side, and emerge from them near the septum. These should be looked for when the flap is being raised, and a cuff of muscle may have to be elevated with the flap to ensure that they are included in the pedi-cle.
In the initial muscle dissection, separating them from the intermuscular septum, the perfo-rating vessels have to be seen and preserved.
With the muscles on each side of the septum
separated, the dissection proceeds in the same manner with both types of transfer. In mobilising the muscles scalpel dissection is used, the plane being extraperiosteal.
The proximal and distal extent of the mobilisation depends on the length of fibula which is being transferred, but over that length they are mobilised completely.
Mobilisation is begun in the direction of the
anterior surface of the bone, with division of the septum which separates the peroneal from the extensor compartment, and mobilisation of the extensor muscles, taking care to avoid
damage to the anterior tibial vessels.
Completion of the mobilisation of the extensors exposes the interosseous membrane from in front.
At this point, the fibula is sectioned proximally and distally at the levels required by the recon-struction, and the interosseous membrane is divided to expose the peroneal vessels which lie behind it.
Section of the bone and division of the membrane, carried out in this order, allows trac-tion to be applied to the membrane while it is being divided, and reduces the risk of injury to the peroneal vessels, in particular the venae comitantes, which are thin walled and easily damaged. It also allows traction to be applied to the bone, once the membrane has been divided, more effectively displaying the structures involved, and making dissection easier and safer.
Division of the interosseous membrane is best
begun distally where the peroneal vessels lie directly behind the septum, and can be immedi-ately identified, mobilised, and distally ligated. The vessels are traced upwards under direct vision, mobilising them and dividing branches directed away from the fibula, making sure at the same time that their attachments to the fibula are preserved.
Proximally, where tibialis posterior is taking origin from the fibula, the vessels run between it and flexor hallucis longus, sometimes through the substance of the latter, from which they then have to be mobilised. Dissection and clearance of the vessels is continued up to their point of origin from the parent posterior tibial vessels, any residual muscle attachments being divided, and leaving the proximal vascular pedicle as the sole attachment.
The length of pedicle which is available for anastomosis is often less than ideal and, particu-larly when the transfer is as an osteocutaneous flap, lies in an awkward position. As a con-sequence vein grafts may be required. When the transfer is osteocutaneous, osteotomies can only be carried out with safety on the anterior or anterolateral aspect of the bone.
Transferred purely as bone, any of the surfaces can be used, other than the one from which the branches of the peroneal vessels are entering.
When bone alone has been transferred, skin
suture with suction drainage is sufficient. When the flap is osteocutaneous the secondary defect is split skin grafted, preferably delayed.
A splint is used for several weeks to support the lower leg and foot, and prevent the development of an equi• nus deformity, until the muscles heal and function normally. An ultimately normal gait is the rule. Clinical usage
This transfer can be made either as one of bone alone, or as a composite with a flap of skin, its
dimensions up to 20 cm x 10 cm. The characteris• tics of the bone, which determine its clinical role, are the length available, up to 30 cm, and its strength. Initially the bone is not strong enough to bear the body weight, but it can undergo hypertrophy to the extent of weightbearing successfully.
It can safely be osteotomised, and should be able to accept osseo-integrated implants.