2011 Flashcards
A 17-year-old boy undergoes excision of a congenital nevus of the scalp. Prior to excision, he underwent placement of a subgaleal tissue expander. Which of the followinggrowth factors is most likely to be upregulated during ischemia in this patient? A) Epidermal B) Keratinocyte C) Platelet-derived D) Transforming E) Vascular endothelial
E) Vascular endothelial
Vascular endothelial growth factor (VEGF) is an important mediator of wound healing and is necessary for angiogenesis. It was originally discovered as a protein secreted by tumor cells to increase the permeability of local blood vessels to circulating macromolecules. It has been shown to increase endothelial growth and migration and enhance glucose transport in the endothelial cell, which is needed to match the increased energy required during angiogenesis. Hypoxia has been shown to be a potent stimulus for the expression of VEGF, and current research has been directed at utilizing VEGF to augment healing and viability in situations of tissue ischemia.
A 10-year-old girl is referred to the office because of a large, full-thickness cranial defect after sustaining a traumatic injury. Reconstruction with a split cranial bone graft is performed. Which of the following is the most likely mechanism by which the bone graft heals? A) Dural ossification B) Osteoconduction C) Osteogenesis D) Osteoinduction E) Vasculogenesis
B) Osteoconduction
The most likely mechanism of split cranial bone graft healing is osteoconduction. The split cranial bone graft is primarily cortical. After it is separated from its blood supply, it serves as a nonviable scaffold for the ingrowth of blood vessels and osteoprogenitor cells from the recipient site. This process of osteoconduction, or creeping substitution, eventually leads to resorption and replacement of most of the graft with new bone. The graft becomes fully osseointegrated with the recipient site.
Spontaneous dural ossification can heal full-thickness cranial defects in infancy. After 12 to 18 months of age, the dura will not spontaneously ossify
Osteogenesis is the primary mechanism of bone graft healing for cancellous or vascularized bone grafts. Because these grafts are revascularized rapidly, osteoblasts survive the transplantation and produce new bone at the recipient site.
Osteoinduction involves the stimulation of mesenchymal cells at the recipient site to differentiate into bone-producing cells. Demineralized bone and bone morphogenetic protein produce new bone primarily by osteoinduction.
Vasculogenesis, the de novo formation of blood vessels from precursor cells, occurs during embryogenesis.
Revascularization of split cranial bone graft occurs by angiogenesis, the production of new vessels from preexisting vasculature.
A 24-year-old woman comes to the office because of painful nodules in both buttocks. She underwent buttock augmentation with injections of liquid silicone by an unlicensed practitioner 4 years ago. Excision of the affected area is performed. Histology of a specimen obtained from the excised tissue is most likely to show which of the following? A) Acellularity B) Calcification C) Granuloma D) Necrosis E) Thrombosis
C) Granuloma
Free silicone liquid has a long history of use for soft-tissue augmentation. Little regulation of the practice and variable degrees of purity of the silicone have resulted in many disastrous complications, often occurring years after the initial injections. Potential adverse sequelae following silicone injection include migration, chronic induration and pigmentary changes, painful subcutaneous nodules, chronic infection, and ulceration. Many of the treated areas require radical resection and reconstruction.
Histologic study of postsilicone injection nodules typically shows granulomas which develop after initial inflammation and fibrosis. Histologic evaluation of typical capsule formation around solid alloplastic prostheses, including breast prostheses, shows acellularity and organized layers of collagen. In the breast, free silicone injection may result in ductal obstruction, which may appear as calcification on mammography. Necrosis may be noted in ulcerative-type complications seen in intradermal injection. Intravascular injection can result in thrombosis and, rarely, embolism, resulting in death.
A 15-year-old boy undergoes negative pressure wound therapy (NPWT) of a traumatic abdominal wound. Which of the following is the most likely mechanism by which NPWT expedites the healing of this wound?
A) Decrease in bacterial burden
B) Deformation of the wound
C) Desiccation of the wound
D) Increase in matrix metalloproteinase activity
E) Maintenance of exudate from the wound
B) Deformation of the wound
Please note: Upon further review, this item was not scored as part of the examination.
The most likely mechanism by which NPWT expedites healing is deformation of the wound. NPWT causes both macrodeformation and microdeformation of a wound. Macrodeformation maintains approximation of the tissues, preventing loss of domain and facilitating earlier closure by delayed primary or secondary intention. Microdeformation at the interface of the sponge and wound bed changes cell shape, which then affects gene transcription via the cytoskeleton (mechanotransduction). These microdeformational forces, for example, stimulate cellular proliferation and angiogenesis in the wound.
The effect of NPWT on bacterial burden is unclear. Some studies have suggested that NPWT reduces bacterial counts in the wound, possibly by direct removal or by increasing blood flow. Other studies have found that NPWT may increase certain bacterial levels.
NPWT prevents desiccation of the wound. The semiocclusive polyurethane drape limits permeability to gases and water vapor and thus maintains a favorable, moist wound environment.
NPWT decreases matrix metalloproteinase activity in the wound. Elevated matrix metalloproteinases inhibit wound healing as well as neovascularization.
NPWT decreases exudate of the wound by removing excess fluid through suction. The reduction in exudate may facilitate wound healing by removing toxic inflammatory mediators and proteinases. Minimizing wound edema also may improve the diffusion of oxygen and nutrients to the wound.
A 63-year-old man comes for evaluation of a dehisced surgical incision 3 weeks after undergoing open reduction of the right ankle. He has a history of coronary artery disease, hypertension, hypercholesterolemia, and poorly controlled type 2 diabetes mellitus. He had a myocardial infarction 2 years ago. Physical examination shows a dehisced surgical incision with exposed tibialis anterior tendon without paratenon. A photograph is shown. The patient refuses free tissue transfer. Which of the following is the most appropriate skin substitute for the wound?
A) Biodegradable bilaminate neodermal matrix (Integra)
B) Biosynthetic wound dressing (Biobrane)
C) Cryopreserved neonatal fibroblast-derived dermal substitute (Dermagraft)
D) Human fibroblast-derived composite skin substitute (TransCyte)
E) Living bilayered skin substitute (Apligraf)
A) Biodegradable bilaminate neodermal matrix (Integra)
Integra is a bilaminate neodermal replacement product that is composed of a biodegradable bovine collagen-glycosaminoglycan (collagen-GAG) matrix underlayer with a silicone outer layer. Although its ?on-label? indication is for burn reconstruction, it also has utility in reconstruction of wounds of exposed bone without periosteum, exposed cartilage without perichondrium, and exposed tendon without paratenon, such as in the scenario described. The collagen-GAG matrix serves as scaffolding for the ingrowth of cells and neovascularization. After regeneration, which takes between 2 to 4 weeks, the silicone outer later is removed and a thin split-thickness skin graft completes the reconstruction by providing epithelial cells over the neovascularized dermal replacement.
Biobrane is a temporary, rather than permanent, bilaminar skin substitute that is constructed of an inner layer, composed of nylon and collagen, which is covered by an outer silicone film. Biobrane serves as a temporary wound dressing, usually in burn patients, where it helps prevent evaporative loss (due to the silicone outer layer) and subsequent wound desiccation. It decreases wound pain and provides a barrier to bacterial infection. Biobrane is removed either before permanent grafting or after epithelialization of the wound has occurred. Derma graft is a dermal substitute composed of neonatal foreskin fibroblasts cultured on a polyglactin mesh, and it is generally used in the treatment of diabetic foot ulcers, where it often is combined with meshed skin grafts.
TransCyte is also a temporary wound dressing. It is similar to Biobrane but has an added biologic layer derived from neonatal fibroblasts that are seeded onto the nylon matrix to produce type I collagen, fibronectin, and glycosaminoglycans. TransCyte is removed either before skin grafting or after epithelialization of the wound. It has been shown to significantly decrease pain and time to epithelialization.
Apligraf, another permanent replacement product, is constructed of type I bovine collagen and cultured neonatal human fibroblasts and keratinocytes. After construction of the dermal matrix equivalent, cultured keratinocytes are applied. It is generally used in the treatment of venous ulcers and diabetic foot ulcers (may take more than one application). Its long-term durability, however, makes it an inappropriate choice in situations with a full-thickness defect with exposed vital structures.
A follow-up photograph of the ankle is shown.
A 67-year-old woman comes to the office for follow-up examination 6 months after debridement of a chronic nondiabetic wound to the lower leg. Following the procedure, the patient was treated with moist dressings. Physical examination shows that the wound is healing less than 15% weekly. Persistent bacteria are suspected. Application of which of the following is the most appropriate nonsurgical management at this time? A) Alginate dressings B) Collagenase C) Film or transparent dressings D) Hydrogel dressings E) Silver ion-impregnated dressing
E) Silver ion-impregnated dressing
Silver ions kill a broad spectrum of bacteria. No resistant organisms have been identified, and it is nontoxic to human cells. Alginates absorb up to 20 times their weight and are used to exudate wounds. Films and transparent dressings are waterproof and would be impermeable to bacterial contamination. Hydrogels are generally waterproof and would prevent bacterial contamination.
