Raymond M. Dunn

Flap models in the rat : a review and reappraisal

The laboratory rat has long provided plastic surgical investigators a model to study many aspects of flap physiology. Clinical advances in reconstructive surgery have succeeded or preceded experimental work, setting the stage for further advances. We have critically reviewed all reports of flap models in the laboratory rat. This has begun with simple skin flaps designed on various areas of the body and continued with a review of free-tissue transfer models. Because of the multitude of as yet unanswered questions remaining, the laboratory rat will invariably continue to be widely used as an investigatory source in this area. This report should allow investigators to select more easily reliable, reproducible experimental models, and, one hopes, to streamline their investigative efforts.

Effect of calcium alginate on cellular wound healing processes modeled in vitro

Although the clinical experience with calcium alginate has been generally good, well-controlled studies examining the effect of such dressings on the processes of wound healing have not been conducted. The healing of cutaneous ulcers requires the development of a vascularized granular tissue bed, filling of large tissue defects by dermal regeneration, and the restoration of a continuous epidermal keratinocyte layer. These processes were modeled in vitro in the present study, utilizing human dermal fibroblast, microvascular endothelial cell (HMEC), and keratinocyte cultures to examine the effect of calcium alginate on the proliferation and motility of these cultures, and the formation of capillarylike structures by HMEC. This study demonstrates that the calcium alginate tested increased the proliferation of fibroblasts but decreased the proliferation of HMEC and keratinocytes. In contrast, the calcium alginate decreased fibroblast motility but had no effect on keratinocyte motility. There was no significant effect of calcium alginate on the formation of capillarylike structures by HMEC. The effects of calcium alginate on cell proliferation and migration may have been mediated by released calcium ions. These results suggest that the calcium alginate tested may improve some cellular aspects of normal wound healing, but not others.

Algorithm for tissue ischemia estimation based on electrical impedance spectroscopy

The purpose of this paper is to present an algorithm developed for real-time estimation of skeletal muscle ischemia, based on parameters extracted from in vivo obtained electrical impedance spectra. A custom impedance spectrometer was used to acquire data sets: complex impedance spectra measured at 27 frequencies in the range of 100 Hz-1 MHz, and tissue pH. Twenty-nine in vivo animal studies on rabbit anterior tibialis muscle were performed to gather data on the behavior of tissue impedance during ischemia. An artificial neural network (ANN) was used to quantitatively describe the relationship between the parameters of complex tissue impedance spectra and tissue ischemia via pH. The ANN was trained on 1249, and tested on 946 ischemic tissue impedance data sets. A correlation of 94.5% and a standard deviation of 0.15 pH units was achieved between the ANN estimated pH and measured tissue pH values.

NOD-scid IL2rgamma(null) mouse model of human skin transplantation and allograft rejection.

Background. Transplantation of human skin on immunodeficient mice that support engraftment with functional human immune systems would be an invaluable tool for investigating mechanisms involved in wound healing and transplantation. Nonobese diabetic (NOD)-scid interleukin-2 gamma chain receptor (NSG) readily engraft with human immune systems, but human skin graft integrity is poor. In contrast, human skin graft integrity is excellent on CB17-scid bg (SCID.bg) mice, but they engraft poorly with human immune systems. Methods. Human skin grafts transplanted onto immunodeficient NSG, SCID.bg, and other immunodeficient strains were evaluated for graft integrity, preservation of graft endothelium, and their ability to be rejected after engraftment of allogeneic peripheral blood mononuclear cells. Results. Human skin transplanted onto NSG mice develops an inflammatory infiltrate, consisting predominately of host Gr1+ cells, that is detrimental to the survival of human endothelium in the graft. Treatment of graft recipients with anti-Gr1 antibody reduces this cellular infiltrate, preserves graft endothelium, and promotes wound healing, tissue development, and graft remodeling. Excellent graft integrity of the transplanted skin includes multilayered stratified human epidermis, well-developed human vasculature, human fibroblasts, and passenger leukocytes. Injection of unfractionated, CD4 or CD8 allogeneic human peripheral blood mononuclear cell induces a rapid destruction of the transplanted skin graft. Conclusions. NSG mice treated with anti-Gr1 antibody provide a model optimized for both human skin graft integrity and engraftment of a functional human immune system. This model provides the opportunity to investigate mechanisms orchestrating inflammation, wound healing, revascularization, tissue remodeling, and allograft rejection and can provide guidance for improving outcomes after clinical transplantation.

Free flap valvular transplantation for refractory venous ulceration

PURPOSE Nonoperative therapeutic approaches to chronic venous ulceration, although effective, often require prolonged dressing care and immobilization with leg elevation. Results of skin grafting, perforator ligation, and valve interpositions and reconstructions improve results of ulcer healing but have not uniformly prevented ulcer recurrence. Our hypothesis is that reconstruction of chronic venous ulcers by excision of the diseased tissue bed and replacement with a free flap containing multiple competent microvenous valves and a normal tissue microcirculation will result in long-term cure of these debilitated patients. METHODS Six patients with chronic venous insufficiency and recurrent ulceration (class 3) underwent excision of ulcers and surrounding liposclerotic tissue beds and reconstruction with fasciocutaneous free flaps (two bilateral). Preoperative and postoperative photoplethysmography was used to assess venous refilling times. Duplex scanning was performed to assess deep venous reflux. RESULTS There were no flap failures. Photoplethysmographic venous refilling times measured on flaps demonstrated significant immediate and long-term increases from preoperative values (all results +3 by Society of Vascular Surgery outcome grading). Long-term maintenance of tissue integrity is shown by absence of recurrent ulceration and no evidence of recurrent tissue lipodermatosclerosis in all flaps at follow-up (8 months to 7.5 years; mean 24 months). No recurrent lipodermatosclerosis was seen on flap biopsy at 2 and 7 years. Separate cadaveric injection studies, including scanning electron microscopy, revealed numerous microvenous valves directed toward the draining pedicle in the flaps used for reconstruction. CONCLUSIONS This is the first comprehensive report providing combined laboratory and clinical evaluation, anatomic rationale, and long-term outcome of surgical rehabilitation of patients with chronic venous ulceration who have undergone microsurgical flap reconstruction.

The rat rectus abdominis myocutaneous flap : a true myocutaneous flap model

Investigations of experimental flaps in lower-order animals have concluded that the cutaneous vascular anatomy of “loose-skinned” animals is not analogous to that of humans. This is particularly relevant with respect to myocutaneous flaps. The interpretation of results of studies in lower-order animals raises questions as to the applicability of these data to the human condition. Objectives: To establish a true myocutaneous flap model in the rat, to define the microvascular anatomy and the cutaneous vascular territory of the rat rectus abdominis myocutaneous flap, and to determine its suitability for additional investigative study of myocutaneous flaps. Methods: Forty-two Sprague–Dawley rats weighing 300 to 400 gm were divided into the following six experimental groups: Group 1 (microvascular anatomy, n = 5), microfil injection and microdissection; Group 2 (n = 5), India ink injection of an isolated superior or inferior epigastric artery pedicle; Group 3, flap control (n = 6); Group 4, superior epigastric (n = 17); Group 5, deep inferior epigastric (n = 16); and Group 6, bipedicle deep inferior epigastric (n = 3). Rectus abdominis myocutaneous flaps based on a single superior or inferior vascular pedicle, or on a double inferior vascular pedicle with an overlying cutaneous island extending from the costal margin to the pubis and anterior to the anterior axillary line, were raised and replaced. Control flap vascular pedicles were transected. Assessment of viability was performed at 7 days using two-dimensional planimetry, tetrazolium, and hematoxylin and eosin stain. Results: Injection studies revealed large (0.1 mm), direct, perforating vessels from the rectus abdominis muscle to the overlying cutaneous island. The cutaneous territory was defined by isolated pedicle India ink injection extended over the vertical muscle axis to the anterior axillary line and for a variable distance across the midline. All controls flaps were nonviable at 7 days. Superiorly based single-pedicle, and double-pedicle inferiorly based, flaps had 97% (SD, 0.03) survival of the cutaneous island. Single inferior pedicle flaps had 77% (SD, 0.07) survival of the cutaneous island with necrosis of the contralateral distal skin island. All flaps had 100% muscle survival. Conclusion: The rat rectus abdominis muscle and overlying cutaneous island constitutes a true myocutaneous territory. This has not been described in a low-order laboratory animal. The flap can be based on single or double, superior or inferior, epigastric vessels with predictable flap survival. The superiorly based and double pedicle flap demonstrates nearly complete viability. This model should serve as a useful investigational tool in the laboratory study of myocutaneous flaps.

A multicenter randomized controlled trial comparing absorbable barbed sutures versus conventional absorbable sutures for dermal closure in open surgical procedures.

BACKGROUND Barbed sutures were developed to reduce operative time and improve security of wound closure. OBJECTIVE The authors compare absorbable barbed sutures (V-Loc, Covidien, Mansfield, Massachusetts) with conventional (smooth) absorbable sutures for soft tissue approximation. METHOD A prospective multicenter randomized study comparing barbed sutures with smooth sutures was undertaken between August 13, 2009, and January 31, 2010, in 241 patients undergoing abdominoplasty, mastopexy, and reduction mammaplasty. Each patient received barbed sutures on 1 side of the body, with deep dermal sutures eliminated or reduced. Smooth sutures with deep dermal and subcuticular closure were used on the other side as a control. The primary endpoint was dermal closure time. Safety was assessed through adverse event reporting through a 12-week follow-up. RESULTS A total of 229 patients were ultimately treated (115 with slow-absorbing polymer and 114 with rapid-absorbing polymer). Mean dermal closure time was significantly quicker with the barbed suture compared with the smooth suture (12.0 vs 19.2 minutes; P<.001), primarily due to the need for fewer deep dermal sutures. The rapid-absorbing barbed suture showed a complication profile equivalent to the smooth suture, while the slow-absorbing barbed suture had a higher incidence of minor suture extrusion. CONCLUSIONS Barbed sutures enabled faster dermal closure quicker than smooth sutures, with a comparable complication profile. LEVEL OF EVIDENCE 1.

Real-time extraction of tissue impedance model parameters for electrical impedance spectrometer

AbstractThis paper presents a new algorithm for real-time extraction of tissue electrical impedance model parameters from in vivo electrical impedance spectroscopic measurements. This algorithm was developed as a part of a system for muscle tissue ischemia measurements using electrical impedance spectroscopy. An iterative least square fitting method, biased with a priori knowledge of the impedance model was developed. It simultaneously uses both the real and imaginary impedance spectra to calculate tissue parameters R0, R∞, α and τ. The algorithm was tested with simulated data, and during real-time in vivo ischemia experiments. Experimental results were achieved with standard deviations of

Adductor magnus perforator flap revisited: an anatomical review and clinical applications.

\sigma _{R_0 } = 0.80\% , \sigma _{R_\infty } = 0.84\%