Recent developments in plastic surgery

Distraction osteogenesis for craniofacial abnormalities

Skin substitutes for burn victims

Genetics and plastic surgery
 
 
 

Distraction osteogenesis for craniofacial abnormalities

Over the past five years distraction osteogenesis to generate new bone has become the surgical treatment of choice for mandibular and midfacial hypoplasias of the craniofacial skeleton.^w1 The commonest craniofacial conditions benefiting from this treatment are hemifacial microsomia (1 in 5000 live births), Treacher Collins syndrome(1 in 25 000 live births), and craniosynostosis syndromes (1 in 20 000 live births). The principle of the technique is that new bone can be induced to form after an osteotomy by distraction along the long axis of the bone at a rate of 1 mm a day.This can be viewed as an endogenous form of tissue engineering (fig A).

Figure A

Fig A(Left) Three month old child with Pfeiffer syndrome (craniosynostosis, hypertelorism, exorbitism, midfacial hypoplasia). Note distorted skull vault due to premature fusion of multiple cranial sutures. (Middle) External distraction frame in place (child has undergone previous skull vault expansion and remodelling). Tracheostomy tube is needed owing to severe airway obstruction from midfacial hypoplasia. (Right) After distraction (tracheostomy has been reversed)

Despite the disadvantage of external appliances, the advantages over conventional surgery are enormous. These include decreased morbidity from the operation as it often obviates the need for bone grafting; lower relapse rates by the induction of bone healing across the resultant gap, giving a greater degree of stability; the added benefit of expanding the overlying soft tissues, which are often deficient in these cases; reduced blood loss, less pain, and a decreased postoperative recovery time due to the reduction of initial bony mobilisation compared with conventional techniques; and less injury to developing dentition.

Skin substitutes for burn victims

A skin substitute should improve wound healing by speeding up the healing process, reducing scarring, and being functionally equivalent to autograft skin. Perhaps the best example is in patients with extensive burns, when there may simply be insufficient unburnt skin available for grafting. In the past porcine skin (xenograft) and cadaveric skin served as excellent temporary biological dressings in the acute phase of treatment. The fundamental problem with these is the allogenicity of the epidermal elements of the tissues and their inevitable rejection by the host after about two weeks. In addition, the problem of hypertrophic scarring and contracture after burn injury is directly related to the depth of the burn and hence the amount of uninjured dermis remaining.

In an attempt to overcome both these problems, several cell free and cell containing matrices have been produced as skin substitutes.^w2-4 Examples include: Integra (Integra Life Science, Plainsboro, NJ), a synthetic, porous bovine derived collagen chondroitin dermis covered with a thin sheet of silicone (fig B); Alloderm (Life Cell, Woodlands, TX), freeze dried human cadaveric dermis from which all cellular material has been chemically removed; Dermagraft (Advanced Tissue Sciences, La Jolla, CA), a synthetic mesh on to which human fibroblasts have been seeded and allowed to proliferate and produce extracellular matrix; Apligraf (Organogenesis, Canton, MA and Novartis Pharmaceuticals, East Hanover, NJ), a mixture of bovine collagen and human fibroblast.

Figure B

Fig B(Left) Four year old child with full thickness flame burns. (Middle) Burns have been excised and substitute skin (Integra) stapled in place. (Right) Early result after split thickness skin grafting on top of newly created artificial dermis

Despite these recent advances skin substitutes are expensive, can be susceptible to infection, and have not yet been shown to produce totally reliable and reproducible results. They are currently recommended only for acute life threatening burns. The quest therefore continues for a cheap, readily available, reliable, reproducible, easy to apply, permanent, non-allogenic substance that heals without contracture.

Genetics and plastic surgery

Many conditions treated by plastic surgeons are genetic, including craniofacial anomalies, congenital limb abnormalities, breast cancer, vascular malformations, and some skin malignancies.

Recently there have been important advances in human molecular genetic research that are directly relevant to clinical plastic surgery. For example it is now possible to identify the genetic mutation for many craniosynostosis syndromes (premature closure of the cranial sutures), including Apert, Crouzon, Pfeiffer, and Saethre-Chotzen syndromes.^{w5 w6} This has led to more accurate clinical diagnosis and genetic counselling. In addition, studies of surgical outcome can now provide new information on treatment prognosis based on genotype. For example, patients with genetically proved Muenke syndrome (a common craniosynostosis syndrome representing about 30% of non-syndromic coronal suture synostosis) have a poorer postoperative outcome than patients with non-syndromic coronal synostosis.^w7

As a result of these findings, proper multicentre trials will be established to determine the most appropriate surgical management for children with genetic abnormalities, based on the results of a specific genetic test.

w1 McCarthy JG, Stelnicki EJ, Mehrara BJ, Longaker MT. Distraction osteogenesis of the craniofacial skeleton. Plast Reconstr Surg 2001;107:1812-27.

w2 Kearney JN. Clinical evaluation of skin substitutes. Burns 2001;27:545-51.

w3 Shakespeare P. Burn wound healing and skin substitutes. Burns 2001;27:517-22.

w4 Balasubramani M, Kumar TR, Babu M. Skin substitutes: a review. Burns 2001;27:534-44.

w5 Johnson D, Horsley SW, Moloney DM, Oldridge M, Twigg SRF, Walsh S, et al. A comprehensive screen for TWIST mutations in patients with craniosynostosis identifies a new microdeletion syndrome of chromosome band 7p21.1. Am J Hum Genet 1998;63:1282-93.

w6 Muenke M, Wilkie AOM. Craniosynostosis syndromes. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The metabolic and molecular bases of inherited disease. New York: McGraw-Hill, 2001:6117-46.

w7 Renier D, El Ghouzzi V, Bonaventure J, Le Merrer M, Lajeunie E. Fibroblast growth factor receptor 3 mutation in nonsyndromic coronal synostosis: clinical spectrum, prevalence, and surgical outcome. J Neurosurg 2000;92:631-6.