An Experimental Human DIEP Flap Model to Investigate Preservation Strategies for Vascularized Composite Allografts and Free Flaps

Our study aims to improve preservation and survival of vascularized composite allografts, and free flaps using human experimental flaps models. Current research mainly relies on animal VCA and free flap models, often using rodent or large animal hand/limb osteomyocutaneous flaps. To begin, perform the preoperative dermal lipectomy marking with the patient and identify the midline from the pubic synthesis to the xiphoid process.

Draw a transverse line approximately seven centimeters above the vulvar commissure. Extend this line laterally about seven centimeters on each side, gently curving it upward to join just below the anterior superior iliac spines. Identify the perforators around the umbilicus using a handheld acoustic doppler probe with eight to 10 megahertz while the patient is in the supine position.

Using a dermographic pen, outline a skin paddle in an elliptical shape of the desired dimensions, including the perforator along its medial border, and extending on both sides of the umbilicus. Prepare and drape the surgical field from the xiphoid process to the upper third of the thighs, including the pubic region, using sterile surgical drapes as routinely performed in standard abdominal surgery. Make a low transverse skin incision along the preoperative marking approximately seven centimeters above the vulva commissure, gently curving toward the anterior superior iliac spines on each side using a number 15 or number 21 scalpel blade.

Detach the umbilicus from the abdominal wall through a circumferential incision down to the hypodermis using a number 15 scalpel blade. Dissect the umbilicus vertically using mayo scissors from the superficial to the deep plane until it is completely freed while preserving its umbilical pedicle. Place a long, loose, non-absorbable suture on either side of the umbilical margin.

Raise the superior abdominoplasty flap in the subcutaneous plane starting from the lower incision and progressing cranially toward the umbilicus. Use a fine tip monopolar electrocautery set to approximately 50 to 70 degrees Celsius and 80 watts in coagulation mode to separate the anterior rectus fascia from the overlying subcutaneous tissue and skin, while maintaining meticulous hemostasis throughout the dissection. As as the dissection approaches the previously isolated umbilical pedicle, continue with fine dissection using Metzenbaum scissors to avoid pedicle injury.

Identify and carefully isolate the two dominant paraumbilical perforators arising from the deep inferior epigastric system. Dissect each perforator circumferentially under direct vision using Stevens or small Metzenbaum scissors, preserving their vascular pedicles. Divide the adipocutaneous panniculus longitudinally along the midline from the center of the lower pubic incision up to the umbilicus using a number 15 blade, followed by monopolar electrocautery set at approximately 50 to 70 degrees Celsius.

Continue the dissection cranially up to the xiphoid region and along the lateral costal margins, keeping the flat pedicles intact and undivided. Ligate the deep inferior epigastric artery perforator pedicle using resorbable 3.0 sutures or automatic clips, and transect the perforator above the fascia with no subfascial dissection. Advance the supra umbilical skin and subcutaneous fat downward and secure the undermined abdominal flap to the inferior incision margin at the midline using a non-absorbable suture, leaving one end of the knot long.

Use the long end of the midline non-absorbable suture, connecting the supra umbilical and pubic areas as a guide to draw the resection line on the excess adipocutaneous panniculus. The DIEP flaps are located below this marked resection line. Completely detach the perforator flap from the surrounding discarded tissue.

Excise the redundant dermo adipose tissue corresponding to the excess skin and fat removed during the abdominoplasty. Then dissect the vascular pedicle under magnification using microsurgical instruments and identify both the artery and the vein. Gently open the arterial lumen with a microvascular dilator.

Catheterize the artery using an 18 to 24 gauge cannula and secure it in the lumen with 5.0 silk suture ligation. Finally, inject contrast agent intra arterially through the catheter into the perforator artery and evaluate the flap under fluoroscopy. The harvested flaps had an average weight of around 198.6 grams, a mean size of 10 centimeters by six centimeters, a pedicle length of around 3.85 centimeters, and an external vessel diameter of 1.2 millimeters.

Arteriography confirmed that all flaps had homogeneous and complete vascular filling, demonstrating good perfusion. There was no significant difference in operative time between six patients undergoing standard abdominoplasty with flap harvest and six retrospective cases without flap harvest. No postoperative abdominal wall deficits or infections were observed in any of the six patients during follow-up.

After catheterization, the flaps were preserved at four degrees Celsius in vacuum-sealed bags and divided into treated and control groups based on perfusion with a cytoprotective agent or University of Wisconsin solution. Histological sections from punch biopsies at different time points showed progressive ischemic changes from zero to 48 hours after storage. We like human anatomical data for realistic VCA and free flap studies.

Current models rely on animals and poorly reflect clinical surgery. Our human perfusion model reduces animal sacrifice and offers anatomical and surgical realism that animal models cannot replace for free flap studies. Our model enables preoperative testing of cytoprotective agents in human skin flaps to evaluate their protective effect against ischemic injury.