Radial Forearm Flap
This flap, raised on the flexor aspect of the fore-arm, is perfused from the radial vessels. Their perforating branches supply the plexus of the investing layer of deep fascia, from which the blood is distributed to the overlying skin. The flap can be designed as a fasciocutaneous flap to transfer soft tissue alone, or in combination with a vascularised length of radial bone as an osteo-fasciocutaneous flap, and also transferring the fascia alone.
In the proximal part of the forearm, the radial vessels lie between the muscle bellies of brachioradialis and flexor carpi radialis, and their perforating branches reach the investing layer of fascia by passing along the intermuscu-lar septum between the two muscles. The tendons of the two muscles separate distal-ly, and the vessels become more superficial, lying on flexor pollicis longus and pronator quadratus.
The effect is to make the septum a less well-defined structure, but the concept of perforating branches from the vessels reaching the fascial layer remains valid.
In the part of the forearm between the sites of insertion of pronator teres and brachio-radialis the intermuscular septum, with its content of branches of the radial vessels, continues laterally over flexor pollicis longus towards the lateral surface of the radius.
There the bone, over a length of approxim-ately 10 cm, has a ‘bare’ area covered only by periosteum, with which the septum merges, its content of branches of the radial vessels forming a plexus on its surface, and supplying the underlying bone. Branches of the radial vessels also supply both the flexor pollicis longus and pronator quadratus muscles in addition to the flexor aspect of the radius from which they take origin, adjoining the ‘bare’ area.
The vessels passing superficially from the
radial artery to reach the investing layer of fascia provide the perfusion source for the fascio-cutaneous element of the flap; the vessels which continue laterally and deeply provide the vascular basis for the transfer of the segment of radius.
The fasciocutaneous element is generally constructed as an island and experience has shown that, provided there is an adequate breadth of the investing layer of tile deep fascia connecting the island to the intermuscular septum with its content of perforators and hence to tile radial vessels, it need not directly overlie the line of the vessels.
The geometry of the transfer largely governs its site. A distal site allows a long proximal vascular pedicle, useful when the transfer is as a free flap; a proximal site allows a long distal pedicle, valuable when a pedicled transfer to the hand is planned. When the transfer is pedicled, the radial vessels pro-vide the sole perfusion source; when a free flap is used, an additional superficial vein is gener-ally retained, available for anastomosis should the need arise.
The flap is raised under tourniquet. Its out-line, and the line of the radial vessels and a suitably sized superficial vein, generally the cephalic, are drawn out on the skin prior to exsanguination of the arm and inflation of the tourniquet. Fasciocutaneous flap
The plane of elevation lies between the investing layer of fascia and the muscles, and the key to the dissection lies in identifying the inter-muscular septum between brachioradialis and flexor carpi radialis. With these muscles and their tendons identified the septum is approached first from one side and then from the other, retracting the related structures to expose the radial vessels.
The vessels are mobilised along with the flap and the intermuscular septum, dividing the multiple small branches to the surrounding muscles. Care should be taken to avoid damage to the terminal branch of the radial nerve which is a close lateral relation of the radial artery in the middle third of the forearm.
Additional skin incisions are made, proxi-mally or distally as required, to allow further mobilisation of the vessels in creating the pedi-cle, and dissection free of the superficial vein. On the arterial side, the proximal limit is the origin of the anterior interosseous artery, which should be retained as a perfusion source for the distal forearm and hand; on the venous side, the proxi-mal limit is the antecubital venous plexus. Osteo(asciocutaneous flap
The skin island is raised as already described as far as the mobilisation of flexor carpi radialis and brachioradialis from the intermuscular septum. Retraction of the flap medially, and brachioradi-alis laterally, exposes flexor pollicis longus and pronator quadratus, and the vessels entering them.
An arbitrary line is drawn over the two muscles in the long axis of the radius between the insertions of pronator teres and brachioradi-alis, a length of approximately 10 cm, the line
along which the muscles and the underlying bone will be sectioned. Medial to this line the vessels entering the muscles are divided as the flap is mobilised, but the vessels entering the muscles lateral to the line and reaching the ‘bare’ area are carefully preserved.
The line is selected so that the radial shaft
is divided in a ratio of one-third lateral and two-thirds medial, the lateral element pro-viding the bony component of the composite transfer. Along the line, the muscles are incised down to the underlying bone and the bone is sectioned using a power saw with a fine blade. The segment of bone has also taken the form of a wedge, cut from the flexor surface of the bone or its lateral surface.
All three forms of resection appear to result in a vascularised segment, as long as the muscles, and the periosteum covering the bare area, are maintained.
Removal of a rectangle of bone leaves a point
of weakness at each end of the site of the resec-tion, and this can be reduced if an additional tri-angle of bone is removed so that the sharp edge at each extremity of the defect is rounded off.
Even so, a protective plaster of Paris is advisable for 4-6 weeks postoperatively while the radius remodels.
1. Fascia/ flap
Vascularised transfer of the investing layer of deep fascia on its own has also been carried out in the form of a segment separated from the overlying superficial fascia and skin. It provides
a vascularised sheet to reconstruct defects of the hand which has the virtues of thinness, and an ability to drape over an irregular surface, able to convert the defect into one capable of accepting a free skin graft.
Management of the secondary defect
The skin defect is split skin grafted. The defect almost invariably includes a considerable area of the visceral paratenon covering the tendon of flexor carpi radialis, and concentration on the raising of the flap is liable to divert the attention of the surgeon from the defect, allowing the paratenon to dry out. It must be kept constantly moist.
Adequate graft take and satisfactory hand function are of para-mount importance, and are achieved best by immobilisation in plaster of Paris. The hand should be immobilised in the position of func-tion with the wrist fully extended. This should be maintained for 14-21 days to ensure firm attachment of the graft before movements are allowed.
Fortunately, even if the graft fails, and an area of bare tendon is exposed, a final deficit in hand function is not inevitable.
With a conservative regime of patience and bland dressings, making sure that a full range of finger and wrist move-ments is maintained throughout, the exposed
tendon will be found to granulate slowly and heal spontaneously.
3. Clinical usage
Among free flaps, the radial forearm has an excellent safety record. It is technically easy to raise, and its popularity has added to this the virtue of familiarity. The skin which it provides is thin and pliable, capable of moulding to an irregular surface. Used as a fasciocutaneous flap, its only adverse factor of significance concerns the secondary defect, its appearance, and the potential for graft failure.
Now that the reason for graft failure is understood and can be coun-tered by maintaining an immobilised wrist until the graft is firmly attached, this is no longer an adverse factor. Used as a composite with bone, the perfusion sources spread along its length allow it to be osteotomised if necessary and, used to reconstruct mandible, this is an advant-age. The cross-sectional area available, however, is not great and it cannot withstand major stress.
As a consequence, it is not suitable for sub-sequent insertion of osseo-integrated implants.