Skin grafting by cross-leg flaps.

Destruction of the skin and subcutaneous tissues of the lower limb is often associated with injury to underyling tendons or bone. Sometimes the skin lesions are allowed to heal by granulation, or they are closed more rapidly by the application of split-skin grafts, and the results of such treatment may be entirely satisfactory. But healing by granulation often leads to chronic ulceration, and healing by split-skin grafting may yield an inadequate and unstable surface, ischaemia developing in each case in consequence of the strangling effect of scar tissue. The importance of securing adequate skin cover before undertaking bone reconstruction operations was impressed repeatedly upon orthopaedic surgeons during the recent war. The most satisfactory skin cover is gained by means of a skin flap that includes subcutaneous tissue ; and a whole-thickness skin flap which gains vascular supply from its margins and through its base may improve the nutrition of underlying tissues. In the case of the leg and foot a convenient donor area is provided by the opposite lower limb , and a flap applied direct from one lower limb to the other is known as a cross-leg flap. Blood supply of flaps-The blood vessels of the skin form a complex pattern and they may be divided into three main units. The first lies in proximity to the papillary layer of the skin and is connected by vertical branches with arterioles of the subdermal and subcutaneous systems. There is also a mid-dermal plexus which is chiefly, but not entirely, venous in constitution. A third plexus, which is situated immediately beneath the dermis, hypertrophies greatly in tube pedicles and open flaps and appears to carry the major burden of vascular nutrition. These facts suggest that, in skin, there is a plexus of vessels with collateral circulation which can be maintained despite such ischaemia as may occur during the raising of a flap. Each of the three vascular systems is superficial to the subcutaneous fat and, unless inclusion of fat is specifically indicated, most of it may be discarded safely. Design of flaps-In planning a cross-leg flap five important considerations must be borne in mind : 1) the basic relative positions of the limbs ; 2) the size and shape of the lesion to be covered ; 3) the ultimate purpose or function of the flap ; 4) the site of the donor flap and disposition of its base ; and 5) the age of the patient and vascular nutrition of the limbs. Basic osi1ion of the two limbs-It is seldom necessary to use “ acrobatic positions.” The recipient area must of course be brought close to the donor area but the position should be easy to maintain and tolerable to the patient. Size and shape of the lesion-The limbs are placed in one of the basic positions (Fig. 1) and the flap is designed on the donor limb in the situation that is most suitable. It is often wise to visualise the completed operation and then to reverse the steps of the procedure (Gillies 1932). The area of skin loss should be outlined carefully, and a replica be cut accurately from jaconet or tinfoil, making allowance for the increase in size of the lesion that always occurs after excision of the scar tissue. The length of flap should equal the width of the deficiency plus the length of its “bridge” (Figs. 2 and 3). An outline is drawn on the donor limb by reversing the jaconet pattern, due allowance being made for the “bridge.” Future purpose of the flap-The general purpose of a flap is to cover an area where skin is lost, or where the quality of skin cannot serve the purpose required of it. If the flap is to cover a weight-bearing area it must include sufficient fat, but not too much. For weightbearing purposes the thickness of the fat layer should not be greater than O 5 cm. Site of the donor area and disposition of its base-In a flap that is well planned the donor area should never encroach upon the tendo Achillis or the anterior surface of the tibia.