Osteocutaneous flap prefabrication based on the principle of vascular induction: an experimental and clinical study

Conventional osteomyocutaneous flaps do not always meet the requirements of a composite defect. A prefabricated composite flap may then be indicated to custom create the flap as dictated by the complex geometry of the defect. The usual method to prefabricate an osteocutaneous flap is to harvest a nonvascularized bone graft and place it into a vascular territory of a soft tissue, such as skin, muscle, or omentum, before its transfer. The basic problem with this method is that the bone graft repair is dependent on the vascular carrier; the bone needs to be revascularized and regenerate. The bone graft may not be adequately perfused at all, even long after the transfer of the prefabricated flap. This study was designed to prefabricate an osteocutaneous flap where simply the bone nourishes the soft tissues, in contrast to the conventional technique in which the soft tissue supplies a bone graft. This technique is based on the principle of vascular induction, where a pedicled bone flap acts as the vascular carrier to neovascularize a skin segment before its transfer. Using a total of 40 New Zealand White rabbits, two groups were constructed as the experimental and control groups. In the experimental group, a pedicled scapular bone flap was induced to neovascularize the dorsal trunk skin by anchoring the bone flap to the partially elevated skin flap with sutures in the first stage. After a period of 4 weeks, the prefabricated composite flaps (n = 25) were harvested as island flaps pedicled on the axillary vessels. In the control group, nonvascularized scapular bone graft was implanted under the dorsal trunk skin with sutures; after 4 weeks, island composite flaps (n = 15) were harvested pedicled on the cutaneous branch of the thoracodorsal vessels. In both groups, viability of the bony and cutaneous components was evaluated by means of direct observation, bone scintigraphy, measurement of bone metabolic activity, microangiography, dye injection study, and histology. Results demonstrated that by direct observation on day 7, the skin island of all of the flaps in the experimental group was totally viable, like the standard axial-pattern flap in the control group. Bone scintigraphy revealed a normal to increased pattern of radionuclide uptake in the experimental group, whereas the bone graft in the control group showed a decreased to normal pattern of radioactivity uptake. The biodistribution studies revealed that the mean radionuclide uptake (percent injected dose of 99mTc methylene diphosphonate/gram tissue) was greater for the experimental group (0.49+/-0.17) than for the control group (0.29+/-0.15). The difference was statistically significant (p<0.01). By microangiography, the cutaneous component of the prefabricated flap of the experimental group was observed to be diffusely neovascularized. Histology demonstrated that although the bone was highly vascular and cellular in the experimental group, examination of the bone grafts in the control group revealed necrotic marrow, empty lacunae, and necrotic cellular debris. Circulation to the bone in the experimental group was also demonstrated by India ink injection studies, which revealed staining within the blood vessels in the bone marrow. Based on this experimental study, a clinical technique was developed in which a pedicled split-inner cortex iliac crest bone flap is elevated and implanted under the medial groin skin in the first stage. After a neovascularization period of 4 weeks, prefabricated composite flap is harvested based on the deep circumflex iliac vessels and transferred to the defect. Using this clinical technique, two cases are presented in which the composite bone and soft-tissue defects were reconstructed with the prefabricated iliac osteomyocutaneous flap. This technique offers the following advantages over the traditional method of osteocutaneous flap prefabrication. Rich vascularity of the bony component of the flap is preserved following transfer (i.e. (ABSTRACT