In-Service Exam
Skin Grafts - Fat - Cartilage Grafts - 2001





Which of the following processes involves the transformation of recipient mesenchymal cells into osteoprogenitor cells resulting from the stimulation of bone morphogenetic protein?

(A) Endochondral ossification
(B) Membranous ossification
(C) Osteochondrosis
(D) Osteoconduction
(E) Osteoinduction

The correct response is Option E.

Osteoinduction describes the process by which tissue types induce cellular differentiation through their actions on each other. Bone morphogenetic protein is stimulated to induce the transformation of perivascular mesenchyme-like cells, known as pericytes, into osteoprogenitor cells.

Endochondral ossification involves the formation of new bone within a hyaline cartilage framework in the epiphysis of the long bones. The process of membranous ossification is primarily responsible for bone formation in the cranial vault and face; this process involves condensation of mesenchymal tissue. Osteochondrosis describes a group of ossification disorders in children. These disorders, which may affect solitary or multiple sites of ossification, are characterized by degeneration of aseptic necrosis of bone followed by reossification. Osteoconduction is the process of tissue ingrowth from the host recipient bed into the grafted material; the bone-producing osteoprogenitor cells play a crucial role in this process.

References
1. Polley JW. Bone grafts. In: Cohen M, ed. Mastery of Plastic and Reconstructive Surgery. Boston, Mass: Little, Brown & Co; 1994;1:102-112.
2. Stratoudakis AC. Principles of bone transplantation. In: Georgiade GS, Riefkohl R, Levin LS, eds. Textbook of Plastic, Maxillofacial and Reconstructive Surgery. 3rd ed. Baltimore, Md: Williams & Wilkins; 1992:39-46.

According to Wolff's law, which of the following factors is critical to the long-term survival of grafted bone?

(A) Presence of membranous bone
(B) Preservation of the periosteum
(C) Preservation of vascularity
(D) Stress

The correct response is Option D.

Wolff's law states that stress is necessary for preservation of the strength and volume of grafted bone. This law has been used to correctly predict the resorption of bone grafted to heterotopic recipient sites and areas lacking the required stress.

Although membranous bone grafts have shown increased long-term survival rates when compared with endochondral grafts, this difference is believed to result from differences in bony architecture as opposed to embryologic origin.

Preservation of an intact periosteum increases graft survival at all stages following transplantation. Delayed revascularization and decreased peripheral bone growth have been demonstrated in bone grafted without periosteum.

Vascularized bone is used for flaps and not for grafts.

References
1. Burwell RG. Osteogenesis in cancellous bone grafts: considered in terms of its cellular changes, basic mechanisms, and the perspective of growth control and its possible aberrations. Clin Orthop. 1965;40:35-47.
2. Friedlaender GE. Current concepts review: bone grafts. J Bone Joint Surg. 1987;69A:786.
3. Hardesty RA, Marsh JL. Craniofacial onlay bone grafting: a prospective evaluation of graft morphology, orientation, and embryonic origin. Plast Reconstr Surg. 1990;85:5.
4. Mulliken JB, Kaban LB, Glowacki J. Induced osteogenesis: the biological principle and clinical applications. J Surg Res. 1984;37:487.
5. Peer LA. The fate of autogenous human bone grafts. Br J Plast Surg. 1950;3:233.

In a patient undergoing lip enhancement using sheet acellular dermal homograft (Alloderm), which of the following is the correct anatomic placement of the graft?

(A) Subdermal placement along the white roll of the lip
(B) Submucosal placement along the white roll of the lip
(C) Submucosal placement along the wet/dry vermilion border of the lip
(D) Intramuscular placement

The correct response is Option C.

Following adequate anesthesia, sheet acellular dermal homograft (Alloderm) should be placed submucosally along the wet/dry vermilion border of the lip. In order to effectively enhance the lips, the surgeon should first create bilateral incisions approximately 0.5 cm from the commissure on both the upper and lower lips; this will allow for tunneling of the Alloderm along this border. After the Alloderm is placed, the lip is stretched, allowing proper sealing of the graft. The ends should then be tapered and placed in a submucosal pocket near the commissure. Suturing is associated with the development of dynamic lip deformities and thus should not be performed.

Because subdermal placement is too superficial, the patient will be predisposed to the development of contour irregularities if the implants are placed at this level. Submucosal placement of the Alloderm along the white roll will result in unnatural lip aesthetics. Alloderm should not be placed within the muscle.

References
1. Rohrich RJ, Reagan BJ, Adams WP Jr, et al. Early results of vermilion lip augmentation using acellular allogenic dermis: an adjunct in facial rejuvenation. Plast Reconstr Surg. 2000;105:409.
2. Tobin HA, Karas ND. Lip augmentation using an Alloderm graft. J Oral Maxillofac Surg. 1998;56:722-727.

Which of the following types of skin graft can be expected to grow proportionately with a young child?

(A) Split-thickness
(B) Full-thickness
(C) Epidermal
(D) Cultured epithelial autograft

The correct response is Option B.

Full-thickness skin grafts can be expected to grow proportionately with a young child. In contrast, split-thickness skin grafts will exhibit some growth, although secondary and/or revision grafting is often required. Epidermal grafts and cultured epithelial autografts will not demonstrate proportionate growth with expansion of the surrounding tissues.

References
1. Baran NK, Horton CE. Growth of skin grafts, flaps, and scars in young minipigs. Plast Reconstr Surg. 1972;50:487-496.
2. Klein L, Rudolph R. H-collagen turnover in skin grafts. Surg Gyn Obstet. 1972;135:49-57.
3. Rudolph R, Ballantyne DL Jr. Skin grafts. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;1:221-274.

Which of the following is a characteristic of unilaminar skin substitutes?

(A) Increased bacterial counts within the wound
(B) Inhibition of granulation tissue
(C) Poor fluid absorption
(D) Poor mechanical protection

The correct response is Option D.

Although unilaminar skin substitutes have been proven to aid in wound debridement and fluid absorption, as well as to decrease the bacterial count within the wound and stimulate granulation tissue, the mechanical protection provided by this synthetic material is poor. Other skin substitutes such as hydrocolloids, hydrogels, and vapor-permeable membranes have been shown to have similar properties.

References
1. Brown AS, Barot LR. Biologic dressings and skin substitutes. Clin Plast Surg. 1986;13:69.
2. Kickhofen B, Wokalek H, Scheel D, et al. Chemical and physical properties of a hydrogel wound dressing. Biomaterials. 1986;7:67.

Bovine collagen is most effective when injected into which of the following anatomic regions?

(A) Epidermis
(B) Dermis
(C) Immediate subdermis
(D) Subcutaneous fat

The correct response is Option B.

Bovine collagen provides the most effective aesthetic result when it is injected into the dermal layer. If injected too deeply (ie, into the subdermal or subcutaneous layers), its effects are highly transitory because resorption is often immediate. However, even with appropriate injection, the desired effect of bovine collagen can only be maintained for a maximum of three to four months, and repeat injections are required for a sustained effect. Injection of bovine collagen into the epidermal layer is often associated with contour deformities.

References
1. Collagen test implant physician package insert. Palo Alto, Ca: Collagen Biomedical; 1995.
2. Fagien S. Facial soft-tissue augmentation with injectable autologous and allogeneic human tissue collagen matrix (autologen and dermalogen). Plast Reconstr Surg. 2000;105:362.
3. Maloney BP. Cosmetic surgery of the lips. Facial Plast Surg. 1996;12:265-278.

Which of the following is most characteristic of hydroxyapatite bone cement?

(A) Exothermic damage to the underlying dura and brain tissue
(B) Gradual loss of contour over time
(C) Osteoinductive growth of new bone
(D) Peripheral ingrowth of bone

The correct response is Option D.

Hydroxyapatite bone cement has been shown to have osteoconductive properties, resulting in growth of new bone over several months following its use in reconstruction. This bone cement is a mixture of amorphous and crystalline calcium phosphate compounds and is recommended for use in nonstress skeletal areas. Because the cement sets endothermically at body temperature, patients are not at risk for any endothermic reactions such as those seen with the use of methylmethacrylate cement. It can be molded and injected into various sites and has not been shown to interfere with craniofacial growth in children. In addition, it maintains its original contour over time. Because the x-ray defraction spectrum of hydroxyapatite cement is similar to bone, scatter effect is not seen on CT scan.

References
1. Burstein FD, Cohen SR, Hudgins R, et al. The use of hydroxyapatite cement in secondary craniofacial reconstruction. Plast Reconstr Surg. 1999;104:1270-1275.
2. Costantino PD, Friedman CD. Synthetic bone graft substitutes. Otolaryngol Clin North Am. 1994;27:1037-1074.
3. Schmitz JP, Hollinger JO, Milam SB. Reconstruction of bone using calcium phosphate bone cements: a critical review. J Oral Maxillofac Surg. 1999;57:1122-1126.

A deep split-thickness skin graft that has been harvested from the scalp has approximately two thirds of the follicular unit (shaft) within the dermis. The percentage of the follicular unit that can be expected to produce hair growth is closest to

(A) 0%
(B) 30%
(C) 50%
(D) 85%
(E) 100%

The correct response is Option B.

If the upper two thirds of the follicular unit (shaft) are transplanted, approximately 30% of the follicles will produce new hair growth. Although the new hairs will be thinner, normal coloring can be expected. The middle third of the hair follicle is partially responsible for hair growth; in contrast, the hair bulb, which in the past was believed to be responsible for hair growth, is actually not required in order to grow new hairs. The bulb is located in the subcutaneous fat beneath the dermis and does contribute somewhat to the growth and health of the hair but is not a necessary factor for growth.

References
1. Arnold J. Pursuing the perfect strip: harvesting donor strips with minimal hair transection. Internat J Aesthet Restorative Surg. 1995;3:148-153.
2. Kim CK, Chol YC. Regrowth of grafted human scalp hair after removal of the bulb. Dermatol Surg. 1995;21:312-313.

Which of the following graft types exhibits the lowest relative volume loss and resorption?

(A) Bone graft
(B) Cartilage graft
(C) Macro-fat graft
(D) Micro-fat graft
(E) Muscle graft

The correct response is Option B.

Because of its unique composition, cartilage is a tissue well formulated for grafting due to its minimal volume loss and resorption. The metabolic rate of cartilage resorption is far less than other human tissues, and its glycolic activity and relatively low consumption rate result from a decreased quantity of cells and a relatively isolated cartilage matrix. Sites that are easily accessible for harvest include the auricular cartilage, rib cartilage, and septum.

Rates of resorption following bone grafting typically depend on graft size and clinical variables. Macro-fat grafts are often unreliable and associated with high rates of resorption. Dermal fat grafts are more commonly used because of their lower rates of resorption and fibrosis. Although micro-fat grafts obtained by injection may be more reliable, resorption rates have been reported as 25% to 50% of the volume of the originally injected fat. Muscle alone is not routinely transferred as a graft; vascularized muscle is more often used in flaps.

References
1. Brent B. Repair and grafting of cartilage in perichondrium. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;1:559-582.
2. Lee WP, Butler PE. Transplant biology and applications to plastic surgery. In: Aston SJ, Beasley RW, Thorne CH, eds. Grabb & Smith's Plastic Surgery. 5th ed. Philadelphia, Pa: Lippincott-Raven; 1997:27-38.

Which of the following characteristics of a full-thickness skin graft has the greatest effect on inhibition of wound contraction?

(A) Epidermal-to-dermal ratio
(B) Percentage of grafted dermis
(C) Presence of muscle at the base of the recipient bed
(D) Skin thickness of the recipient bed
(E) Thickness of the entire graft

The correct response is Option B.

Full-thickness skin grafts inhibit wound contraction by accelerating the rate of dissolution of myofibroblasts from the wound. Because of this, it is the percentage of grafted dermis, rather than the absolute thickness of the total graft, that has the greatest effect on inhibition of wound contraction.

The epidermal-to-dermal ratio, skin thickness of the recipient bed, and presence of muscle within the recipient bed play only minor roles in inhibiting wound contraction.

References
1. Glat PM, Longaker MT. Wound healing. In: Aston SJ, Beasley RW, Thorne CH, eds. Grabb & Smith's Plastic Surgery. 5th ed. Philadelphia, Pa: Lippincott-Raven; 1997:3-12.
2. Peacock EE Jr, Cohen IK. Wound healing. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;1:161-185.

Following split-thickness skin grafting, which of the following dressings can be used at the donor site to minimize discomfort, reduce the risk for infection, and decrease healing time?

(A) Bismuth tribromophenate-impregnated gauze (Xeroform)
(B) Heterograft
(C) Hydrocolloid polymer complex (DuoDerm)
(D) Silicone membrane-nylon fabric composite (Biobrane)
(E) o-Tolylazo-_-naphthol- (Scarlet Red-) impregnated gauze
The correct response is Option C.

An occlusive dressing consisting of a polyurethane foam and a hydrocolloid polymer complex (DuoDerm), or a semiocclusive dressing consisting of synthetic adhesive moisture vapor permeable films (eg, Op-Site, Tegaderm) will minimize patient discomfort, reduce the risk for infection, and decrease healing time.

Fine mesh gauzes (eg, Scarlet Red, Vaseline, Xeroform) use the semiopen technique of wound healing. Epithelialization and infection rates are favorable, but, when compared with other dressings, pain and discomfort are greater.

Another version of the semiopen wound-healing technique involves the use of a semipermeable silicone membrane and a knitted nylon fabric covalently bonded to porcine collagen (Biobrane). This method is more comfortable for the patient but is associated with a higher rate of infection following skin grafting.

Biologic dressings (eg, cadaveric skin homografts, heterografts, porcine xenografts, amniotic membranes) are frequently associated with marked inflammation of the wound, delayed epithelialization, and prolonged wound healing times.

References
1. Feldman DL. Which dressing for split thickness skin graft donor sites? Ann Plast Surg. 1991;27:288-291.
2. Michie DD, Hugill JV. Influence of occlusive and impregnated gauze dressings on incisional healing: a prospective, randomized, controlled study. Ann Plast Surg. 1994;32:57-64.
3. Smith DJ, Thomson PD, Bolton LL, et al. Microbiology and healing of the occluded skin-graft donor site. Plast Reconstr Surg. 1993;91:1094-1097.