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 t o custom create the flap as dictated dy the complex geometry of the defect. The usual method to prefabricate an osteocutaneous flap is to harvest a no nvascularized bone graft and place it into a vascular territory of a soft t issue, such as skin, muscle, or omentum, before its transfer. The basic pro blem with this method is that the bone graft repair is dependent on the vas cular 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 techn ique in which the soft tissue supplies a bone graft. This technique is base d on the principle of vascular induction, where a pedicled bone flap acts a s the vascular carrier to neovascularize a skin segment before its transfer . Using a total of 40 New Zealand White rabbits, two groups were constructe d as the experimental and control groups. In the experimental group, a pedi cled scapular bone flap was induced to neovascularize the dorsal trunk skin by anchoring the bone flap to the partially elevated skin flap with suture s in the first stage. After a period of 4 weeks, the prefabricated composit e naps (n = 25) were harvested as island naps pedicled on the axillary vess els. In the control group, nonvascularized scapular bone graft was implante d under the dorsal trunk skin with sutures; after 4 weeks, island composite naps (n = 15) were harvested pedicled on the cutaneous branch of the thora codorsal vessels. In both groups, viability of the bony and cutaneous compo nents was evaluated by means of direct observation, bone scintigraphy, meas urement of bone metabolic activity, microangiography, dye injection study, and histology. Results demonstrated that by direct observation on day 7, th e skin island of all of the flaps in the experimental group was totally via ble, like the standard axial-pattern nap in the control group. Bone scintig raphy revealed a normal to increased pattern of radionuclide uptake in the experimental group, whereas the bone graft in the control group showed a de creased to normal pattern of radioactivity uptake. The biodistribution stud ies revealed that the mean radionuclide uptake (percent injected dose of Tc -99m methylene diphosphonate.gram tissue) was greater for the experimental group (0.49 +/- 0.17) than for the control group (0.29 +/- 0.15). The diffe rence was statistically significant (p < 0.01). By microangiography, the cu taneous component of the prefabricated flap of the experimental group was o bserved to be diffusely neovascularized. Histology demonstrated that althou gh the bone was highly vascular and cellular in the experimental group, exa mination of the bone grafts hi 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, w hich revealed staining within the blood vessels in the bone marrow. Based on this experimental study, a clinical technique was developed in whi ch a pedicled split-inner cortex iliac crest bone flap is elevated and impl anted under the medial groin skin in the first stage. After a neovasculariz ation period of 4 weeks, prefabricated composite flap is harvested based on the deep circumflex iliac vessels and transferred to the defect. Using thi s clinical technique, two cases are presented in which the composite bone a nd soft-tissue defects were reconstructed with the prefabricated iliac oste omyocutaneous flap. This technique offers the following advantages over the traditional method of osteocutaneous nap prefabrication. Rich vascularity of the bony componen t of the flap is preserved following transfer (i.e., the bony component of the flap is vascularized bone graft rather than nonvascularized bone graft) . The soft-tissue component of the prefabricated flap can be obtained in ac cordance with the thickness of the defect, offering a thin-skin paddle in a desired orientation relative to the bony component. To the best of the author' knowledge, this is the first report in the Engli sh literature to describe the use of a bone flap as the vascular carrier in flap prefabrication.