Michael J. Yaremchuk

RELATIVE ANTIGENICITY OF COMPONENTS OF A VASCULARIZED LIMB ALLOGRAFT

At present, the transplantation of vascularized limbtissue allografts can be achieved only with generalized host immunosuppression, which results in significant systemic toxicity, thereby precluding their clinical use. A better understanding of the immunogenic mechanisms of these allografts may permit less toxic and thus clinically applicable means of host immunosuppression. In this study, individual vascularized limb tissues (skin, subcutaneous tissue, muscle, bone, and blood vessels) and a whole limb were transplanted microsurgically across a strong histocompatibility barrier in rats. The respective cell-mediated and humoral immune responses generated in the hosts were determined by means of mixed lymphocyte cultures by radioactive 51Cr release assays and compared. No single tissue predominated in the elicited immune response. Rather, the various tissue components interacted with the host immune system in a complex but predictable pattern with differing timing and intensity. Surprisingly, the whole-limb allograft elicited less immune response than did allografts of its individual components. The data presented here also serve as a foundation for further elucidation of the immunogenic mechanisms of vascularized limb-tissue allografts.

Complications and toxicities of implantable biomaterials used in facial reconstructive and aesthetic surgery: a comprehensive review of the literature.

The use of implantable biomaterials has become an integral part of aesthetic and reconstructive surgery of the face. Metals are used for fracture fixation devices, whereas polymers are used primarily for bone or soft-tissue substitution. This review of the scientific literature examines the risks and complications of these materials. First, we present an overview of commonly used materials. Second, we address general considerations of toxicity relevant to all biomaterials. Third, we present data from a large number of clinical series on the incidence of complications for individual materials used in specific applications.

De novo cartilage generation using calcium alginate-chondrocyte constructs.

&NA; These studies investigated the utility of calcium alginate as a biocompatible polymer matrix within which large numbers of chondrocytes could be held successfully in a three‐dimensional structure and implanted. Further, the ability of chondrocyte‐calcium alginate constructs to engraft and generate new cartilage was examined. Chondrocytes isolated from calf shoulders were mixed with a 1.5% sodium alginate solution to generate cell suspensions with densities of 0, 1.0, 5.0, and 10.0 × 106 chondrocytes/ml. The cell suspensions were gelled to create disks that were placed in subcutaneous pockets on the dorsums of nude mice. The alginate concentration and CaCl2 concentration used to make the disks also were varied. A total of 20 mice were implanted with 67 bovine chondrocyte‐calcium alginate constructs. Samples with an initial cellular density of at least 5.0 × 106 chondrocytes/ml demonstrated gross cartilage formation 12 weeks alter implantation. Cartilage formation was observed microscopically in specimens with a cellular density as low as 1.0 × 106 chondrocytes/ ml. The histoarchitecture of the new cartilage closely resembled that of native cartilage. Cartilage formation was independent of CaCl2 concentration (15 to 100 mM) or alginate concentration (0.5% to 4.0%) used in gel polymerization. (Plast. Reamslr. Surg. 97: 168, 1996.)

Injectable tissue-engineered cartilage using a fibrin glue polymer

The purpose of this study was to demonstrate the feasibility of using a fibrin glue polymer to produce injectable tissue-engineered cartilage and to determine the optimal fibrinogen and chondrocyte concentrations required to produce solid, homogeneous cartilage. The most favorable fibrinogen concentration was determined by measuring the rate of degradation of fibrin glue using varying concentrations of purified porcine fibrinogen. The fibrinogen was mixed with thrombin (50 U/cc in 40 mM calcium chloride) to produce fibrin glue. Swine chondrocytes were then suspended in the fibrinogen before the addition of thrombin. The chondrocyte/polymer constructs were injected into the subcutaneous tissue of nude mice using chondrocyte concentrations of 10, 25, and 40 million chondrocytes/cc of polymer (0.4-cc injections). At 6 and 12 weeks, the neocartilage was harvested and analyzed by histology, mass, glycosaminoglycan content, DNA content, and collagen type II content. Control groups consisted of nude mice injected with fibrin glue alone (without chondrocytes) and a separate group injected with chondrocytes suspended in saline only (40 million cells/cc in saline; 0.4-cc injections). The fibrinogen concentration with the most favorable rate of degradation was 80 mg/cc. Histologic analysis of the neocartilage showed solid, homogeneous cartilage when using 40 million chondrocytes/cc, both at 6 and 12 weeks. The 10 and 25 million chondrocytes/cc samples showed areas of cartilage separated by areas of remnant fibrin glue. The mass of the samples ranged from 0.07 to 0.12 g at 6 weeks and decreased only slightly by week 12. The glycosaminoglycan content ranged from 2.3 to 9.4 percent for all samples; normal cartilage controls had a content of 7.0 percent. DNA content ranged from 0.63 to 1.4 percent for all samples, with normal pig cartilage having a mean DNA content of 0.285 percent. The samples of fibrin glue alone produced no cartilage, and the chondrocytes alone produced neocartilage samples with a significantly smaller mass (0.47 g at 6 weeks and 0.46 g at 12 weeks) when compared with all samples produced from chondrocytes suspended in fibrin glue (p < 0.03). Gel electrophoreses demonstrated the presence of type II collagen in all sample groups. This study demonstrates that fibrin glue is a suitable polymer for the formation of injectable tissue-engineered cartilage in the nude mouse model. Forty million chondrocytes per cc yielded the best quality cartilage at 6 and 12 weeks when analyzed by histology and content of DNA, glycosaminoglycan, and type II collagen.

Acute and definitive management of traumatic osteocutaneous defects of the lower extremity

Twenty-two lower extremity osteocutaneous defects resulting from high-energy trauma were managed from the onset of injury to rehabilitation by a collaborative effort between orthopedic and plastic surgeons. Emergency debridement of devitalized soft tissue and bone, external fracture stabilization, and serial debridements prepared the wound for closure with predominantly free-muscle transfers performed an average of 17 days (range 3 to 43 days) after injury. Cancellous or vascularized fibula grafting, depending on defect size, was performed an average of 9 weeks (range 6 to 16 weeks) after muscle flap closure. In this group of patients, whose average injury severity score was 18 (range 9 to 45) and whose average segmental bone defect was 8 cm (range 3 to 18 cm), the average time after injury to full weight bearing was 61 weeks (range 39 to 120 weeks). The early infection rate was 14 percent. Two extremities were amputated. There have been no chronic infections. Follow-up has ranged from 9 to 34 months.

Tissue engineered neocartilage using plasma derived polymer substrates and chondrocytes

&NA; This study demonstrates that fibrin monomers can be polymerized into moldable gels and used for the encapsulation of isolated chondrocytes. This biologically derived scaffold will maintain three‐dimensional spatial support, allowing new tissue development in a subcutaneous space. Chondrocytes isolated from the glenohumeral and humeroradioulnar joints of a calf were combined with cyroprecipitate and polymerized with bovine thrombin to create a fibrin glue gel with a final cell density of 12.5 × 106 cells/ml. The polymer‐chondrocyte constructs were implanted subcutaneously in 12 nude mice and incubated for 6 and 12 weeks in vivo. Histologic and biochemical analysis including deoxyribonucleic acid (DNA) and glycosaminoglycan quantitation confirmed the presence of actively proliferating chondrocytes with production of a well‐formed cartilaginous matrix in the transplanted samples. Control specimens from 12 implantation sites consisting of chondrocytes alone or fibrin glue substrates did not demonstrate any gross or histologic evidence of neocartilage formation. Moldable autogenous fibrin glue polymer systems have a potential to serve as alternatives to current proprietary polymer systems used for tissue engineering cartilage as well as autogenous grafts and alloplastic materials used for facial skeletal and soft‐tissue augmentation. (Plast. Reconstr. Surg. 101: 1580, 1998.)

The Latissimus Dorsi Muscle: A Fresh Cadaver Study of the Primary Neurovascular Pedicle

The primary neurovascular pedicle of the latissimus dorsi muscle was studied in 50 fresh cadaver dissections and pertinent dimensions and anatomic relations was recorded. Some findings applicable to clinical reconstructive surgery are: 1. Vascular pedicle of 11 cm mean length (subscapular-thoracodorsal artery and vein). 2. Consistent T-shaped relationship among subscapular artery, thoracodorsal artery, circumflex scapular artery, and serratus arterial branch(es). 3. Large serratus anterior branch(es) from the thoracodorsal artery (1.1 mm mean diameter). 4. Consistent posterior location of neurovascular hilus at muscle junction. 5. Bifurcation of neurovascular structures at the hilus into superior and lateral intramuscular bundles (86 percent of dissections), making various surgical options with the latissimus dorsi skin-muscle flap possible. 6. Lengthy thoracodorsal nerve (12.3 cm mean length). 7. Low incidence of atherosclerosis in the subscapular artery (8 percent) and no significant atherosclerosis seen in the thoracodorsal artery.

The effect of rigid fixation on the survival of onlay bone grafts: an experimental study.

Much attention has recently been focused on rigid fixation as a method of improving fracture healing. Whether such fixation, when applied to onlay grafting, improves graft take and volume is unknown. To examine this question, we compared survival of both endochondral and membranous grafts fixed rigidly and nonrigidly in areas of low motion (snout) and high motion (femur) in a rabbit model. Gross morphology, histologic analysis, and graft volume kinetics were evaluated. Findings demonstrate that in areas of high motion, the application of rigid fixation improves graft survival, whereas in a low-motion region, no differences in graft volume retention as a function of fixation were observed. Histologically, no differences with the method of fixation employed were seen, and similar revascularization patterns were noted. By kinetic analysis, rigid fixation appears to exert its most profound effect early in the postgraft period. Membranous bone grafts remain superior to endochondral grafts under all circumstances. From these studies, we conclude that rigid fixation is the method of choice in all circumstances where onlay bone grafts may be exposed to motion, shear, and torsional forces.

Transdermal photopolymerization of poly(ethylene oxide)-based injectable hydrogels for tissue-engineered cartilage.

Transdermal photopolymerization, a minimally invasive method for implantation, was used to subcutaneously place a mixture of polymer and isolated chondrocytes to regenerate cartilage tissue in vivo. Semi-interpenetrating networks of varying proportions of poly(ethylene oxide)-dimethacrylate and poly(ethylene oxide) and primary bovine articular chondrocytes were implanted in athymic mice. Four mice (12 implants) were harvested at 2, 4, and 7 weeks. Chondrocytes survived implantation and photopolymerization and formed neocartilage containing 1.5 to 2.9% wet weight collagen and 4 to 7% glycosaminoglycan. Thirty-five percent of the total collagen was type II collagen. Histologic analysis exhibited tissue structure resembling neocartilage, and safranin O staining demonstrated glycosaminoglycan distribution throughout the hydrogels. This study demonstrates the potential use of transdermal photopolymerization for minimally invasive subcutaneous implantation of hydrogels and chondrocytes for in vivo cartilage regeneration.

Management of the medial canthal tendon in nasoethmoid orbital fractures : the importance of the central fragment in classification and treatment

The medial canthal tendon and the fragment of bone on which it inserts (“central” fragment) are the critical factors in the diagnosis and treatment of nasoethmoid orbital fractures. The status of the tendon, the tendonbearing bone segment, and the fracture pattern define a clinically useful classification system. Three patterns of fracture are appreciated: type I—single-segment central fragment; type II—comminuted central fragment with fractures remaining external to the medial canthal tendon insertion; and type III—comminuted central fragment with fractures extending into bone bearing the canthal insertion. Injuries are further classified as unilateral and bilateral and by their extension into other anatomic areas. The fracture pattern determines exposure and fixation. Inferior approaches alone are advised for unilateral single-segment injuries that are nondisplaced superiorly. Superior and inferior approaches are required for displaced unilateral single-segment injuries, for bilateral single-segment injuries, and for all comminuted fractures. Complete interfragment wiring of all segments is stabilized by junctional rigid fixation. All comminuted fractures require transnasal wiring of the bones of the medial orbital rim (medial canthal tendon-bearing or “central” bone fragment). If the fracture does not extend through the canthal insertion, the canthus should not be detached to accomplish the reduction.