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GMS Current Topics in Otorhinolaryngology - Head and Neck Surgery

Deutsche Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie e.V. (DGHNOKHC)

ISSN 1865-1011

Operative treatment of functional facial skin disorders

Review Article

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  • corresponding author Marc Oliver Scheithauer - Department of Otorhinolaryngology, University of Ulm
  • Gerhard Rettinger - Department of Otorhinolaryngology, University of Ulm

GMS Curr Top Otorhinolaryngol Head Neck Surg 2005;4:Doc18

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Veröffentlicht: 28. September 2005

© 2005 Scheithauer et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Abstract

The skin is the principal interface between the body and the surrounding world and thus serves as a protective barrier against trauma, temperature extremes and radiation. With receptors for pressure, movement, heat and cold, it also acts as sensory organ and through sweat secretion plays a role in thermoregulation and electrolyte metabolism. Not all of these functions are relevant to facial skin, however, cosmetic aspects are of vital importance.

Disorders primarily affect the protective skin function in defect and scar areas. For operative correction, the following principles should be applied: Minimization of scar development by adherence to indicated incision lines in the face, preferred use of local skin flaps for defect coverage in order to obtain optimal results regarding texture, complexion and sensitivity of skin, as well as consideration of aesthetic units. Recent developments in this field are tissue culture, occlusive dressings, and the use of growth factors.

Age-related skin changes with impairment of cosmetic function are characterized by the development of creases and looseness of skin. Rejuvenation has become an important segment of skin surgery. For surface treatment, especially of creases and acne scars, various types of laser treatment are employed. Deeper lines can be filled with filler materials. The integration of the superficial musculoaponeurotic system (SMAS) into face lift procedures has lead to more viable and natural results. Due to protruding tissue, blepharoplasty of the upper lid is often carried out in combination with forehead lift and eyebrow lift procedures.

The optimized use of growth factors and synthetic materials, which serve as a matrix, are aimed at skin replacement which mimics the quality and functions of skin as closely as possible. On the whole, however, the reconstruction of defect through local tissue transfer is still considered as the treatment of choice.

Keywords: reconstructive facial surgery, flap plasty, wound healing, rejuvenation, laser, tissue cultivation, growth factors


1. Structural characteristics of facial skin

1.1 Structure of skin

The skin (cutaneous membrane) consists of an epithelial layer (Epidermis) and a connective tissue layer (also corium or dermis, Figure 1 [Fig. 1]). The underlying subcutaneous layer connects the skin to muscle tissues and bones. The epidermis is free of vessels and is made up of an outer, cell-free cornified layer (Stratum corneum) and a deeper germinal layer (stratum basale) which provides a papillary and thus fixed link with the corium. In this papillary layer of corium lies the subepidermal vascular plexus which provides nutrients to the adjacent basal layer of epidermis. The corium is composed of densely interwoven layers of collagenous and elastic fibers whereas the subcutis consists of loose connective tissue and fatty tissue. The subcutis serves as a sliding layer of skin against the underlying tissues (especially periosteum and muscular fascia) [1]. Furthermore, the thickness of this layer determines the shape of certain facial areas (the cheek bones for instance) and in other regions of the face, the subcutaneous layer is completely absent (for example eyelids, nasal columella, anterior part of auricle). The average thickness of facial epidermis is approximately 0.6 mm, the corium has an average thickness of about 1.5 mm and the subcutis of 6 mm or more. The approximate thickness of layers can be determined via sonography or high resolution magnetic resonance tomography [2].

Our skin is composed of about 65% of water, 22% of proteins and minerals, and 13% of fat. It is the largest water store of the body with one third of the fluids contained in corium and subcutis. The thickness and thus the form of the skin is always dependent on its fluid and fat content. Furthermore, skin is the largest (approx. 2 m2) and heaviest (approx. 10 kg) organ of the body. Skin can bear a tensile force of 90 kg, a property, which is primarily due to the fibers of the corium [1]. The basal layer of epidermis also contains melanocytes which provide protection against ultraviolet radiation. Moreover, in sunlight skin thickness may increase up to 10-fold and thus reach light protection factor 4 after a period of 4 weeks (skin thickening due to actinic dermatitis).

1.2 Skin creases and the superficial musculoaponeurotic system (SMAS)

There is a general distinction between natural (also age-related) lines, tension lines and relaxed skin tension lines (RSTL). The muscles of expression are directly connected to the corium, so the skin follows muscle movement. This leads to the development of typical lines such as horizontal forehead lines (musculus frontalis), vertical glabellar lines (musculus procerus, a branch of musculus frontalis at the root of nose), crow's feet lines (musculus orbicularis oculi) and radial lip lines (Musculus orbicularis oris). These lines are usually perpendicular to the muscle fibers and are visible in muscular contractions. Other lines such as the nasolabial fold develop because the muscles of the nasal slope (musculus levator labii superioris alaeque nasi) are directly connected to the circular musculus orbicularis oris.

Langer's lines of skin cleavage were determined through incisions, especially of the trunk skin, in which defects align ovally according to the direction of corium fibers [3]. In contrast to the RSTL and the wrinkle lines, these are not relevant in facial skin surgery.

RSTL are lines which are visible after complete relaxation of the skin [4]. These correspond to a great extent to natural skin folds - only in the canthus area variations are possible. It is generally recommended to place incisions along existing skin lines and to follow the RSTL in younger patients (Figure 2 [Fig. 2]).

The superficial musculoaponeurotic system (SMAS) divides the subcutis into two layers and is the direct continuation of the epicranial aponeurosis in the facial region. At the lower edge of the parotid gland, the SMAS gradually becomes the platysma. Nerves and vessels lie in the deep fat layer underneath the SMAS, perforating vessels penetrate the muscles and are attached to the subepidermal vascular plexus of corium. The SMAS distributes the force of the nasal musculature. Its innervation, as that of the muscles of expression an the platysma, occurs via the facial nerve [5], [6], [7].

1.3 Nerves and nerve endorgans

One square centimeter of corium contains an average or 450 receptors of which approx. 200 are nocireceptors, 100 pressure receptors, 12 cold receptors, and 2 thermoreceptors, as well as 4 meters of nerve fibers [8].

Sensory function (touch): Changes of the cells' status are passed on to Meissner's corpuscles in the papillary layer. Each of theses tactile corpuscles is connected to approximately 50 nerve fibers and can differentiate oscillations in lower frequency ranges (10 to 30 Hz). Moreover, 60 million Merkel cells in the corium transmit speed and strength of the stimulus [9].

In the face, the distance between these sensors is only 1 to 5 mm (especially in the lips). The sense of touch can recognize pressure differences of 0.005 g [10], [11].

Thermoreceptors: Thermoreceptors are present in the outer skin layers and react to temperatures between -18 °C and 44 °C. These receptors reach an especially high density in the chin and nose areas (9 to 13 receptors per cm2). Temperatures outside the mentioned reference range are perceived as pain [12].

1.4 Appendages of skin

Sweat glands: Sudoriferous glands are responsible for the acid mantle of skin (pH 4.5) and are predominantly present in the forehead area. They are not present in the red of the lips. Trough the evaporation of sweat, these glands play an important role in thermoregulation and salt excretion (approx. 0.4%) [13], [14].

Sebaceous glands: Sebaceous glands are predominantly located at the hair follicles but also occur in a free form (red of lips). These glands and the sweat glands keep the kin smooth and provide a protective barrier against bacteria [15], [16].

Hair: The scalp is covered with approx. 100,000 hairs per square centimeter. These display an average growth of 0.33 mm per day and primarily serve as protection against heat and ultraviolet radiation.

1.5 Blood and lymphatic vessels

Larger arteries are only present in the subcutis. At the transition to the corium, a widely branching network of vessels supplies nutrients to hair and glands. Nutritive supply of the skin is provided by the papillary plexus (rete arteriosum subpapillare) from which arterioles and capillaries extend to the connective tissue fibers. The density of papillary capillaries varies between 20 and 60 per cm². As blood pressure in the capillaries is higher than the pressure in the surrounding tissue, they always remain open. Due to blood supply, in surgical interventions either local flaps without a defined afferent vessel (random pattern flap) or larger and longer skin flaps with a defined supplying vessel (axial pattern flap) can be used. The veins also form vascular networks which end in skin veins with large lumens situated on the muscular fascia.

The same applies to lymphatic vessels with lymph predominantly draining via subcutaneous lymphatic capillaries. These capillaries form a widely distributed network of lymphatic vessels which forms a unit with blood vessels and connective tissue. The direction of flow is determined by the valves, the smooth muscle cells and rhythmic contractions of the lymphatic vessel walls. An imbalance of lymph quantity and transport capacity or lymph composition (colloid osmotic pressure) leads to lymphedema in the interstitial area [17], [18], [19], [20].


2. Functions of facial skin

The predominant function of the skin is its protective role as interface between the body and the outer world. Furthermore, especially in the facial area, skin plays an important aesthetic role.

2.1 Mechanical protection

The superficial cornified layer (stratum corneum) provides protection against injuries. Underneath this layer lies an elastic sliding layer with a desmosomal supporting structure in the intercellular gaps which displays a grill-like trajectory arrangement. The epidermis is interlinked with the corium in a zip-like structure: Epidermal reticular cones are situated in the papillaries of corium. The dermis also contains a system of elastic fibers which, in the deeper layers of corium, run parallel to the skin surface, then raise towards the surface and become vertical in the papillaries. The skin is thus an elastic structure which can compensate for moderate trauma whereas the subcutaneous fat layer absorbs stronger shocks and shear stress. Scars, especially those covering lager surfaces, lead to impaired protection as mechanical energy may reach deeper structures (muscles and bones) without attenuation.

2.2 Radiation protection

Energetic radiation (x-ray, ultraviolet radiation) causes additive, irreversible skin alterations. This especially affects renewable tissues as the epidermal basal cells. Degeneration of collagen fibers in the corium (elastosis), dilatations of skin veins (teleangiectasia), cornification disorders and finally precancerosis and malignoma are the consequences. The desmosomes of the basal cell layer are destroyed (acantholysis), and an accompanying radiation vasculitis entails an exudative inflammatory process (radiation vasculopathy with mediasclerosis) [21]. As a result, the skin becomes atrophic and sclerotic.

Protective mechanisms of the skin are the formation of melanin pigments, hyperkeratosis and repair processes of DNA. These mechanisms require an intact skin structure, especially good vascularization which is not the case in tissue defects and large scars.

2.2 Protection against temperature extremes

Excessive heat at temperatures above 50°C leads to peroxidation of membrane lipids, to the dissociation of macromolecular enzyme-protein-complexes, and to protein denaturation. Burns are classified into four degrees of severity. Necroses (third- and fourth-degree burns) are filled with granulation tissue and a thin epidermis with impaired function grows over this tissue. The healing of the defect occurs in a cicatrisation process which can lead to the development of keloids and contractions [22].

In cold injuries, there is a delayed oxygen dissociation in hemoglobin with an increase in carbon dioxide solubility [23]. The water crystallizes and triggers cell necrosis. The peripheral parts of the face (nose and ears) are especially affected. There are four severity degrees of cold injuries with similar symptoms as in burns [24], [25].

2.3 Thermoregulation

The highest quantities of sudoriferous glands can be found in the palms of the hands and the soles of the feet, fewer quantities are present in the head area (i.e. forehead skin).Thus, facial skin plays a minor role in thermoregulation [26].

2.4 Sensitivity

Sense of touch as well as pain and thermoreceptors are of vital importance (see above). They provide protection against mechanical, thermal and chemical noxae. Various pain receptors react to the stimuli mentioned above. Dull and diffuse pain is transmitted via marrow-free nerve fibers whereas localized pain is transmitted trough marrow-rich nerve fibers. The free ends of the nerve fibers are situated in the epidermis. In the face, somatoafferent pain is mediated via neuronal connections of the nociceptive trigeminal system. In scar regions these functions are not fully provided so that in operative interventions scars should be kept to a minimum. The highest degree of reinnervation can be reached with transposition or rotation flaps while in full skin grafts only a limited sensitive quality has to be expected. For transplants in which microvascular anastomosis was performed, the sensitivity of skin could not be increased despite nerve reconstruction. Therefore a complex nerve suture is not recommended [27], [28]. Reinnervation of unmyelinated C-fibers and myelinated A-δ-nociceptors in the myocutaneous flap could be demonstrated with evoked cortex potentials [29].

The quality of reinnervation depends to a large extent on the properties of the site of transplantation. Chances of sensitive reinnervation are significantly higher if a fresh wound is treated with a primary graft. In secondary treatment, especially if fibrous scar tissue develops after transplantation, the probability of sensitive recovery is very low. Nerve regeneration in healing transplants tends to be very heterogeneous. This corresponds to the clinical findings in which complete sensitivity is hardly seen in examinations although patients feel that sensory protection is sufficient [30], [31].

2.5 Immunologic functions of skin

The protective mantle of healthy epithelial skin can usually prevent invasion by pathogens. Bacteria, viruses, and parasites which surmount this barrier are immediately recognized as foreign organisms by tissue bound macrophages and are destroyed through phagocytosis. This leads to a mediator mediated inflammatory response of the organisms (for details see chapter 3.2). If local immunoreactions are not sufficient and infection cannot be prevented, the Langerhans cells (dendritic epidermal T cells) located between keratinocytes are activated. The main function of these cells is the concentration of antigen material and due to their large surface they are especially suitable for antigen presentation to B cells. Therefore, Langerhans cells are mainly responsible for the initiation of T cell immunoresponse. Dendritic cells develop from progenitor cells in the bone marrow [32], [33], [34].

As facial skin represents only a small portion of the total skin surface, disorders and operative treatment of immunologic skin function is not relevant for this paper and cannot be influenced by surgical measures.

2.6 Aesthetics and shape

To most people, the cosmetic aspect of facial skin is as important as its protective function. Besides disfiguring scars and malformations also aging processes play an important role. This comprises formation of lines (forehead, glabella, nasolabial fold, perioral and periocular lines) which can be managed through surface treatment (for example laser), tissue augmentation (for example Gore-Tex) or with face lift techniques.

The form of certain facial structures as eyelids, nasal ala and auricle is rather determined by the underlying supporting structures than by the properties of skin (tarsal plate, alar cartilage, auricular cartilage). If the skin possesses sufficient elasticity and appropriate dimensions, it will adapt to these supporting structures, however, these may also be deformed by scar contractions or other skin changes. This can occur especially in tissues with poor stability such as the tarsal plate and thin cartilage. When performing reconstructions it is therefore critical to choose skin flaps of appropriate dimensions and to avoid tension.

Especially in areas which usually lack a layer of subcutaneous fatty tissue and where form is the result of skin properties and the underlying structures (for example auricles, nasal columella), an excessively thick skin would lead to deformities.


3. Basic principles of plastic reconstructive facial skin surgery

3.1 Objectives of surgical measures

The primary objectives are the reconstruction of an intact skin surface without scar deformities of adjacent regions (such as eyelids, nasal ala and lips) as well as the achievement of functional form (for example the form of nostrils) without conspicuous cosmetic consequences. For defect coverage, texture, complexion, and the position of remaining scars are of vital importance. The aim of reconstruction of an intact skin surface also includes restoration of the protective functions of facial skin against mechanical, thermic, chemical and radiation injuries. The maintenance of sensitivity in the defect area also plays a significant role. Only facial skin can provide these functions as well as favorable surface properties. Therefore, local (donor site neighbors defect) and regional (donor site near defect) flap plasties are paramount compared to free transplants (also called pedicle flaps) in operative treatment of defect-associated functional disorders. Negative consequences of surgical rehabilitation, especially relevant cosmetic and functional disorders (motility) are to be avoided [35].

In some exceptional cases of smaller skin defects without functional and aesthetic impairments, healing by second intention represents a treatment option. This applies above all to the regions of the medial canthus, the lateral alar cartilage, the nasolabial fold, the temples and the concave surfaces of the anterior part of the auricles and of the retroauricular sulcus (Figure 6) [36].

In operative treatment of functional facial skin disorders, that is primarily of wounds, defects and scars with impairment of function (for example scar deformities) and of aesthetics, many aspects need to be observed and carefully planned.

3.2 Wound healing

Wound healing essentially occurs in three consecutive phases [37]:

Exudative phase (day 1 to 3)

A temporary fibrin matrix forms a "natural" dressing.

Neutrophil granulocytes and monocytes, activated by complement C5a and tumor necrosis factor-α, chemokines and interleukin 8, induce phagocytosis of bacteria and cell debris in the wound area. Activated monocytes are transformed into macrophages and synthesize tissue-degrading enzymes (elastase, glycosidase, matrix metalloproteinases) in order to provide space for repair.

Proliferative phase (day 4 to 7)

Keratinocytes, fibroblasts and angioblasts migrate from the wound edge through the temporary fibrin matrix into the center of the wound where they proliferate and differentiate. The fibrin matrix is then transformed and produces cell adhesion proteins (integrins) which enable the adhesion of cell clusters. Endothelial cells increase cell proliferation and vasopermeability through vascular endothelial growth factor (VEGF). Collagen synthesis of fibroblasts is mainly stimulated by thrombocyte growth factors. This whole system is subject to self-regulation through positive and negative feedback mechanisms. Granulation tissue is the result at the end of the proliferative phase.

Reparative phase (from day 8)

Fibroblasts synthesize type III collagen (vessels), type I collagen (skin, bones, tendons) as well as collagen types IV (basal membrane) and VII (for dermoepidermal adhesion). Some fibroblasts are converted into myofibroblasts which develop actin-myosin filaments (also referred to as cross-links) which contract longitudinally (wound contraction). In the mean time, reepithelialisation of the wound surface takes place as keratinocytes interconnect in a zip-like structure (free-edge effect). The phase of reconstruction is characterized by the functional balance of matrix metalloproteinases (MMP) and their inhibitors, tissue inhibitor of matrix metalloproteinases (TIMP).

After primary surgical closure, an uncontaminated skin wound shows postoperative epithelialisation already on the second day following the intervention and from day 4 it is protected against bacterial invasion [38]. Stability regarding tear-resistance develops from day 8 onwards (formation of cross-links and beginning of wound contraction) and stops increasing after three weeks. Due to good perfusion with low hydrostatic pressure in the venous and lymphatic system, conditions for wound healing in the face are favorable. Therefore, sutures can be removed as early as 5 to 7 days postoperative, especially if tension is controlled by subcutaneous sutures. In areas with a high density of sebaceous glands (for example tip of nose), removal of skin sutures should be carried out earlier in order to prevent epithelialized stitch scars. Special attention needs to be paid to the risk of hyperpigmentation of facial scars if exposed to sunlight which persists until approximately 60 days postoperative. In this period, the use of sunscreen with a high protection factor is recommended.

Bandages in the facial area are predominantly used for protection, compression to prevent swelling and for the promotion of wound healing. For this purpose, especially occlusive dressings are suitable. They promote quick epithelialisation, reduce wound pain, lower the infection rate, and may lead to better cosmetic results. In occluded wounds, the quantities of necrotic and fibrinous tissue are lower and increased humidity promotes angiogenesis as well as the interaction between growth factors and target cells. Consequently, the content of fibroblasts and inflammatory cells is reduced which can result in smaller scar dimensions [39]. In normal wound healing, a wound dressing is no longer needed from the fifth day postoperative at the latest.

Alloplastic tissue adhesion with arcylates is recommended for the treatment of smaller skin lesions especially in children. When applied to abrasions in spray form, these substances function like an occlusive dressing. In animal models these substances have been shown to have neither toxic effects on tissue nor to be detrimental to wound healing [40]. The use of percutaneous sutures lead to greater wound closure and wound stability, however, also tissue reaction and bacterial invasion was higher than following the use of acrylate glue. A study has shown that after seven days there was no difference in wound stability between wounds treated with tissue adhesives and wounds which were closed with primary sutures [41]. Wound healing can also be enhanced with allogenic fibrin glue especially in larger wounds that are treated with skin grafts. Animal tests have shown that this effect depends on the thickness of the applied fibrin layer. If an excessively thick fibrin film is used (more than 0.06 ml per cm2), this might even impair revitalization of the transplant [42].

3.3 Aesthetic units, creases and tension lines

Aesthetic units represent the areas of facial skin which are determined by the natural shape of the face which should, if possible, completely be replaced in defect treatment, even if the defect is smaller than the corresponding unit (Figure 3 [Fig. 3]). The final result should ideally be the reconstruction of an aesthetic unit as one complete surface without scar lines. The treatment of defects which affect several aesthetic units should be carried out for each unit individually. It is certainly not possible to respect these ideal recommended procedures in all circumstances depending on defect location, size and adjacent regions. Besides the aesthetic units of the face, subunits for certain regions, especially for nasal reconstructions, can be identified (Figure 4 a, b [Fig. 4]). However, the principle of aesthetic units not only applies to defect management but also to the region of excision for skin advancement. Also in this case, the aim should be an uninterrupted aesthetic unit.

Crease and tension lines (RSTL) are to be used as guidelines for excision of facial skin (Figure 5 [Fig. 5]). Along these lines, incisions are less conspicuous, the risk of gaping wound edges is lower, and wound closure causes minimal tension. Scars crossing these lines can at least partially be aligned parallel to the RSTL with Z-plasties or multiple W-plasties (Figure 6 [Fig. 6]) [43], [44].


4. Management of facial skin defects

In this presentation, only basic principles and special aspects to consider can be discussed. Detailed information can be obtained from surgical references or in the papers of the various associations of otolaryngology and head and neck surgery [45].

4.1 Defect management with free grafts

Free skin grafts require a recipient site with good perfusion at the wound edges and in the wound base. Split-skin grafts (with a thickness of 0.2 to 0.5 mm) provide favorable healing conditions and can be employed as mesh graft to cover larger wound areas. Disadvantages of this technique are strong contractive tendencies and poor cosmetic results. Therefore, split-skin grafts are not commonly used in the facial area.

Full skin grafts (with a thickness of 0.5 to 1 mm) comprise epidermis and dermis without subcutaneous fatty tissue. The risk of contraction is lower than in split skin, and because of its thickness, the transplant may also be used for treatment of deeper defects with significant wound bed granulation. Retroauricular and supraclavicular skin are the best-suited harvest sites, but also with this technique, cosmetic outcome is merely moderate in most cases. This procedure is appropriate for elderly patients who reject complex defect reconstruction in several sessions (Figure 7 a, b [Fig. 7]) [46].

Auricular skin/cartilage grafts (composite grafts) are suitable for surface reconstructions with remolding [47], [48]. These grafts show a low risk of contraction, however, healing is rather problematic. Nutrient supply is only possible via the graft edges because penetration of vessels from the wound bed trough the cartilage portion is not possible. Thus, the size of these skin/cartilage transplants is limited to a diameter of approximately 1.5 cm. These grafts are of limited suitability for skin surface reconstruction for cosmetic reasons. They are rather appropriate as interior lining in nasal ala reconstruction or as mucosal cartilage transplant from the nasal septum for tarsus-conjunctiva reconstruction.

Grafts with microvascular anastomosis are used for defect coverage in lager wound areas especially after preoperative irradiation [49], [50]. Fasciocutaneous forearm grafts display good malleability and can be employed as tandem flaps for the inner and outer lining of defects [51]. This method, however does not lead to satisfactory cosmetic results in de facial area. Musculocutaneous flaps for deeper defects and skin/bone grafts for reconstructions of the midfacial region or the mandible represent additional alternatives, especially in the creation of a vital wound bed for extaoral and intraoral implants. Drawbacks of this method are a time-consuming procedure, possible vascular complications, and complications at the donor site (for example wound healing disorders and scar contractions). Due to the texture and complexion of the grafted skin, aesthetic results are often unfavorable [52], [53], [54], [55].

4.2 Defect management through regional pedicle flaps

Local or regional flap plasties are the best way of treating defects in the facial area with respect to cosmetic outcome and function. These procedures, however, require precise planning and excellent knowledge of available treatment options. Nutrient supply to the transplanted skin occurs via the flap pedicle in two alternative ways:

1. Supply via a defined artery (axial pattern flap):

These flaps with a thin pedicle can be of considerable length. Examples of such flaps are the median or oblique forehead flap (Figure 8 [Fig. 8]) as well as the nasolabial flap with caudal pedicle (Figure 9 [Fig. 9]). A special form of this flap is the myocutaneous island flap in which the nutrient artery supplying the peripheral skin island is located inside the muscular pedicle. Characteristic examples are the myocutaneous island flap of the pectoralis major and the latissimus dorsi flap. Because of the large volume of flap pedicles and the differences in skin structure, myocutaneous flaps are only used in exceptional cases for deep defects in the facial area (for example in the treatment of parotid gland carcinoma with skin resection) [56], [57], [58].

2. Nutrient supply of random pattern flaps occurs via subcutaneous arteries in the ubiquitous subepidermal vascular plexus. Their statistical distribution allows for excision of skin flaps of limited size regarding the ratio of flap length and width. As skin in the facial area is usually well perfused, a length-width-ratio of 3:1 is considered to be suitable for random pattern flaps, however, particular circumstances need to be taken into account (age, smoking, previously existing scars) [59], [60].

According to the method of skin transfer, the following flap types are distinguished:

Advancement flap: This is a linear skin advancement which is frequently carried out in the treatment of gaping wound edges by undermining adjacent skin [61], [62], [63].

Transposition flap: The flap pivots about a point (90° or more) at the flap pedicle. In this procedure, raised tissue at the foot of the flap often requires correction or removal of the entire flap pedicle in a second session. Examples are defect management in the nasal area with forehead flaps of various lengths (Figure 10 a, b [Fig. 10]) [64].

Rotation flap: Rotation flaps are especially suitable for the facial area because they provide a one-stage procedure in which skin from the adjacent regions is transferred to the defect. Its complexion and texture matches that of the recipient site. Rotation flaps can be formed in every facial region. Special forms are rhomboid flaps according to Limberg or Dufourmentel as well as multilobed flaps [65], [66].

Bilobed flap: In a bilobed flap, the first flap servers as rotation flap for defect management and the second flap is used as transposition flap to close the donor area. This technique uses the fact that the second flap may be smaller than the first one and comes from a region with very mobile skin so that wound closure becomes possible [67], [68], [69]. Example: Defect coverage of the lateral slope of nose with an adjacent rotation flap and management of the harvest site with a glabellar transposition flap.

Island flap: Island flaps with subcutaneous pedicle consist of a skin island which is supplied via the pedicle of subcutaneous fatty tissue. The skin island is either directly advanced into a neighboring defect (subcutaneous sliding flap) or is pulled through a skin tunnel into a remote defect. This procedure is mostly carried out after excision of a composite graft from the concha of ear and less frequently in the facial area as the resulting scars (aesthetic unit) often lead to poor cosmetic outcome [70], [71]. If a subcutaneous pedicle island flap can be used, it may represent an alternative to full skin grafts (Figure 11 a, b [Fig. 11]).

In addition to required flap dimensions the aesthetic units of the donor and recipient sites, the resulting scars in both areas (RSTL) and tensions (line between the foot of the flap and the remotest defect edge) are important aspects to be observed when planning defect treatment with local or regional flaps. During flap transfer, distortion of the donor region has to be avoided (especially in the lower eyelid, nasal ala and lip areas) [72].

4.3 Skin expansion

With skin expansion in the donor area, graft surface can be enlarged and primary closure of the donor site defect becomes possible. Expanders in various sizes and shapes are frequently used in the forehead region because the frontal bone provides a stable base for expansion. The skin is usually filled through an implanted subcutaneous port system (PTE = prolonged tissue expansion) (Figure 12 a, b [Fig. 12]) [73], [74], [75].

Shifting of the hair line at the flap edges can be avoided and primary closure of the harvest site defect is possible especially when of forehead flaps are used. Histologically, expanded skin displays flattening of the reticular layers, an increased division rate of basal cells and an increase in fibroblast proliferation as well as lipocyte atrophy.

4.4 Treatment of facial skin defects through epithesis

Epitheses primarily serve shape reconstruction and are thus used to restore body integrity in extended defects. Furthermore, they can fulfill certain functions. Epitheses for the nose have a positive effect on moisturization of the nasal mucosa and reduce crust formation. An ear epithesis provides the possibility of wearing glasses.

Adhesive epitheses are attached with skin-friendly glue, however, they may lead to skin macerations. Adhesive epitheses are especially suitable for nose, orbit and auricle replacement.

Bone-anchored epitheses exploit osseointegration of titanium screws in vital bone. The screws, coated with titanium plasma, which are attached to bone, can bear functional strain. They may be used in conjunction with magnets, bridge constructions or three-dimensional carrier plates. After completion of the healing process they provide a secure anchorage, but this is a time-consuming, complex and costly procedure. Especially in tissues with preoperative irradiation there is a risk of implant loss. Indications for epithetic management are situations in which other surgical methods are too complex, unsafe (preoperative irradiation, scars) or not satisfactory from an aesthetic point of view (Figure 13 a, b [Fig. 13]) [76], [77], [78], [79].

4.5 Defect management in specific facial areas

Defect management of nose, eyelids, lips and cheeks comprises a range of surgical treatment options which are derived from the above mentioned principles and require careful planning as indicated. Further discussion of these procedures is beyond the scope of this paper. Details are described in the relevant literature [80], [81].


5. Other functional disorders of facial skin

5.1 Scars and keloids

Scars, hypertrophic scars, and keloids only develop if an injury or incision extends to the papillary layer of skin. Superficial lesions heal without leaving scars.

Hypertrophic scars are defined as excessive, uneven scars of red color which do not exceed the wound area and disappear within a few months or years. Keloid are characterized by strong cicatrisation which exceeds the original area of injury and affects healthy skin without disappearing [82]. Therefore, keloids clinically display properties of a benign tumor with a high probability of recurrence after excision.

There are several theories on keloid development:

• Myofibroblasts do not differentiate into fibrocytes which are normally subject to apoptosis. This causes disorders in the development of collagen fiber networks with unstructured deposition of fibers which then bind together due to high proteoglycan content [83].

• Lymphocytes remain in the wound region and produce angiogenetically active cytokins. These induce an intensification of angiogenesis with increased cellular metabolism. Furthermore, a limiting apoptotic process does not take place [84].

• Increased levels of the profibrotic cytokin transforming growth factor-β (TGF-β) with corresponding increase in the number of fibroblasts invoke synthesis of type-I and type-IV collagen. Higher TGF-β-levels might be caused by wound tension with impairment of feedback mechanisms [85].

The disorder is not limited to a certain phase of wound healing but affects several wound healing processes, especially at the cellular level, which entails increased collagen synthesis [86]. Hypertrophic scars can be avoided by preventing wound tension and placing incisions parallel to the RSTL. Suture material also plays a vital role; monofil sutures are preferable [87]. After one year, hypertrophic scars usually adapt to the skin surface.

For keloid prophylaxis, intralesional corticosteroid injection is recommended (Table 1 [Tab. 1]) [85].

Keloids mainly occur in the retroauricular region and are extremely rare in other areas of facial skin [88]. Excision without further treatment leads to extensive relapse within 2 years in 80% of the cases. Better results were obtained with intramarginal excision, if possible combined with intralesional corticoid injection every 3 months over a period of 2 years [89], and compression treatment.

Compression treatment for relapse prevention after keloid excision has the following effects [90]:

• reduced perfusion leads to a decrease in alpha II macroglobulin levels with an intensified collagen degradation by collagenase.

• low chondroitin-IV-sulfate levels also lead to increased collagen degradation.

• stabilization of mastocytes decreases angiogenesis and thus the production of extracellular matrix.

• hypoxia finally leads to fibroblast degeneration and collagen degradation.

Compression treatment over a period of several weeks is difficult with respect to patient compliance and should therefore only be considered for extended burn scars. In the auricular area, however, especially for ear lobes, this form of treatment can easily be used [91].

Today, radiation therapy is widely rejected due to the risk of secondary malignoma. Exceptions are elderly patients who cannot undergo surgery and suffer from keloids with significant functional impairments (very rare) [82].

New treatment approaches are currently being tested. With interferon (INF) a and β, collagen synthesis can be reduced. Administered in doses between 0.01 and 0.1 mg, a regression of keloids was observed and 1 out of 10 patients achieved complete remission [92]. On the whole, however, interferon treatment is uncertain, characterized by numerous side effects, and expensive. For this reason the substance is not yet used to a larger extent. In the future, the development of treatment options on the cellular level is to be expected.

5.2 Laser surgery of tumors, scars and other skin disorders

Various forms of laser with different wavelengths and energies are used for the treatment of skin alterations. For tumor management (for instance rhinophyma), tissue removal plays a predominant role whereas in vascular processes (hemangioma, teleangiectasies) the coagulant properties of laser are being used (Figure 14 a, b [Fig. 14]). Table 2 [Tab. 2] provides an overview of the characteristics of different laser types and the corresponding indications for the treatment of skin diseases [93], [94], [95], [96], [97], [98], [99], [100], [101].

5.3 Functional disorders in age-related skin changes

Age-related skin alterations mainly comprise formation of wrinkle lines in certain characteristic locations: perioral, periorbital, forehead, cheek, upper eyelid and nasolabial fold. Furthermore, aging skin loses its elasticity and decreased resilience leads to gravity-related slackness of facial skin.

Indications for skin resurfacing include prominent scars, lines, pigmentation changes, pachyderma and other skin alterations. According to findings, chemical peeling [102], abrasion (for example with a rotating brush or diamond) [103] or various laser procedures for removal or coagulation are recommended. For the treatment of atrophic scars, dermal and subcutaneous volume replacement with autogenous materials (for example fatty tissue) or non-biological tissues can be considered as an alternative for conventional methods such as surgical scar revision. Augmentation of deep lines or scars with alloplastic polymers is an additional option. Silicones (Silastic®) and ePTFE (expanded polytetrafluoroethylene), also known as Gore-Tex [104], are the most frequently utilized materials.

Especially acne scars can display various properties - from superficial macula and indented areas to multiple fistulae. The latter represent a special challenge in surgical treatment [105]. Today, surface laser treatment of skin scars is frequently used. Carbon dioxide laser and Er:YAG-laser can easily be applied because they are well absorbed in water, the main component of skin. The advantages of Er:YAG-laser are gentle removal of the keratin layer with thermic stress being lower than in carbon dioxide laser procedures. Penetration depth of Er:YAG-laser rays with (5 J/cm² with a diameter of 3 mm) is estimated to range between 5 and 15 µm. The effect of laser therapy was proven in histological studies: thermic energy in the adjacent tissues first induces skin contraction by dehydration, followed by an inflammatory process that entails angiogenesis and thus leads to an increase in fibroblast activity. Consequently, skin creases are filled with newly formed collagen and the skin surface becomes even [106]. Laser with ablation mode only, such as short-pulsed Er:YAG laser, are only suitable for superficial scars. Dual-mode Er:YAG laser and carbon dioxide laser have additional coagulation properties and can thus be employed for the management of deeper scars [107], [108], [109], [110], [111], [112]. There are contradictory opinions concerning laser surgery of deeper nasolabial folds as this method bears the risk of pigmentary alterations [113].

Meta-analysis of 27 publications on laser resurfacing for facial acne scars [114] has shown no evidence of the efficacy of laser treatment of atrophic or indented acne scars due to lack of data from randomized studies in which various laser types were compared.

Besides carbon dioxide and Er:YAG laser with ablation and coagulation mode, other nonablative laser treatments of facial skin are possible. Flash lamp pulsed dye laser [115], diode laser and Nd:YAG-Laser [116] are said to remodel dermal collagen. As only limited effects can be expected from these procedures, they are only considered for the treatment of minor skin defects such as lesions caused by light exposure or fine wrinkle lines.

Due to age-related decrease in skin elasticity, excess tissue from the fold of the upper eyelid may protrude over the eyelid rim with visual field impairment. In this process, several mechanisms are of importance:

The condition may be caused or accompanied by eyebrow ptosis which can be compensated to a certain degree by contraction of the frontal muscle (symptomatic development of horizontal forehead lines). In advanced stages of tissue laxity, however, this is no longer possible. Furthermore, excess skin from the eye lid protrudes over the eyelid rim (dermatochalasis), possibly accompanied by herniation of orbital fatty tissue due to tears in the muscular tissue. The protruding skin fold is frequently caused by lateral eyebrow ptosis. Often resection of excess skin and prolapsed fatty tissue (blepharoplasty) is not sufficient [117], [118].

In such cases, an additional eyebrow lift procedure is required which is either carried out endoscopically (without skin resection) or via a bicoronary approach (with skin resection), according to requirements. The operation is based on a subperiosteal removal of soft tissue with periosteum dissection at the supraorbital point as well as myotomies of Mm. depressor supercilii, corrugator supercilii, and procerus. During the intervention, is important that the supratrochlear and supraorbital vessel and nerve tract remain intact. Afterwards fixation of the mobilized frontal soft tissue complex in an elevated position is performed with sutures attached to bone screws [119].

While age-related alterations of the eyebrows usually become visible towards the end of the third decade, increased formation of skin creases on forehead, cheeks, chin and neck is only observed in the mid-forties or later. Following gravity, two vectors of force acting on the skin in den facial and neck area are distinguished: a central, perpendicular vector that changes the forehead skin and the skin of the periorbital region, and a lateral vector in oblique downward direction which especially affects the cheeks. To determine the indication for facelift procedures (rhytidectomy), subdivision of the face into the three following zones has proven useful: First zone: forehead with eyebrows, second zone: periorbita (upper and lower eyelids), third zone: cheeks. Face lifts (rejuvenation) are based on the augmentation of skin in the three zones, opposite to the direction of vector force (lateral and superomedial vector lift) [120]. Especially for correction of cheek skin several techniques have been successfully applied. For this purpose, the soft tissue portions of the face are divided into three layers: the superficial layer comprising skin and subcutis, the intermediate layer including the SMAS, the muscles of expression, intermuscular fatty tissue, as well as the motor and sensory facial nerves, and finally the deep layer of submuscular fat, periosteum, and the insertions of the sensory nerves [121]. A conventional surgical approach is the lifting of skin and subcutis towards the retroauricular region. Newer techniques utilize dissection of the SMAS-layer in order to lift the SMAS through doubling or for fixation to the fascia of the temporal muscle with slight tension after limited resection. In deep plane rhytidectomy, which represents an advanced form of SMAS lift procedure, the sub-SMAS layer on the fascia of M. masseter is dissected. The advantage of this procedure is that besides an SMAS lift an additional resection of buccal fatty tissue can be performed [122].

5.4 Hypertrophy of sebaceous glands (rhinophyma)

Rhinophyma is a tumor-like hypertrophy of sebaceous glands on the tip of the nose and nasal ala. Growth of bulbous structures can lead to obstruction of the nostrils and thus impair respiration [123], [124].

The aim of surgical interventions is the removal of excess tissue and remolding of skin contour. Reepithelialisation occurs from remaining parts of epithelium on the basis of the sebaceous glands which, however, it might also be the reason for relapse. All commonly utilized procedures are based on the same principles, the only difference resides in the method of tissue removal. Scalpels or shavers are most frequently used; fewer bleeding and thus better sight during intervention can be achieved with an electric knife or laser treatment [94], [125], [126]. It is important to limit resection to the skin without causing injuries in the subcutaneous tissue or even the alar cartilage.

5.5 Hair loss

Hair loss in the facial area especially plays a role in the eyebrow area (for example following burns or trauma). Sweat from the forehead region freely flows into the eyes and cause irritations. Missing eyebrows can either be replaced with transposition flaps from the scalp or via free hair grafts [127], [128].

In free hair graft procedures, individual hair is harvested mostly from the back of the head using a cylindrical punch with a diameter of 2-4 mm (punch grafts) and is then implanted into the recipient site with small stitches. When harvesting such skin-hair transplants, incisions need to be parallel to the hair shaft to prevent damage of hair follicles. Full-thickness skin cylinders comprise 6 to 8 hair follicles so in a single session, about 30 individual transfers can be performed [129], [130], [131].

If eyelashes are missing, a part of the eyebrows can be transplanted for reconstruction. The eyebrow graft is sutured to the margin of the eyelid with the hair facing in the desired direction [132].

Even vibrissae of the vestibulum nasi can serve as autologous eyelash replacement [133].

5.6 Hyperhidrosis (auriculotemporal syndrome)

Hyperactivity of sudoriferous glands in the facial area are especially relevant in auriculotemporal syndrome (also known as Frey's syndrome or gustatory sweating). This condition occurs after parotidectomy, however, it requires treatment in only 15% of the cases. Hyperhidrosis is caused by misdirected growth of dissected parasympathetic nerve fibers into sudoriferous glands of the skin (misdirected regeneration). Intraoperative interposition of temporoparietal fascia or sternocleidomastoid/platysma muscle transfer as well as splitting of N. auriculo-temporalis or plexus tympanicus have not shown significant success [134], [135], [136]. Transposition of an SMAS flap into the retromandibular fossa is said to be a more efficient treatment option. Following this procedure in 160 patients, no indication of hyperhidrosis could be found with iodine-starch test [137].

Intracutaneous botulinum toxin type A injection represents an alternative treatment option to surgical interpositions [138].

5.7 Operative treatment options for sensory disorders of skin

Sensory reinnervation by reconstruction of dissected nerves, for example of trigeminal branches (N. alveolaris inferior and N. lingualis) is very difficult. Attempts to repair continuity defects with Gore-Tex tubing or autologous veins have produced poor results. Only short lesions of the N. alveolaris inferior might be repaired successfully with autologous vein grafts because its position along the canalis alveolaris inferior is straight and the wound area is immobile. Due to anatomical conditions, N. lingualis does not meet these requirements, so that neural regeneration is impaired. As the vein conduit can act as a blocking membrane it is not considered to be useful in the reconstruction of longer neural defect zones. At present, this additional intraoperative procedure is viewed as being too complex for an uncertain clinical outcome and is thus not justified [139], [140].


6. Future developments

6.1 Biotechnological skin replacement

Surgical procedures for defect coverage are restricted to a certain defect size because of donor site limitations. An ideal scenario would be the utilization of free skin transplants of required size which match complexion and texture of the recipient site. One approach is the growth of a replacement dermis (Integra®, Johnson & Johnson WM). In this procedure, a two-layer polymer with a silicone surface and a porous network of collagen fibers as underlying structure is inserted into the defect. High biodegradability provides for physiologic wound healing and "neodermis" formation. The superficial silicone layer is removed after a few weeks in a surgical procedure and is replaced with full skin grafts [141], [142], [143].

Autologous skin cultivation is a widely utilized procedure for the treatment of patients with severe burns. For this method, 2 cm2 of axillary skin are brought into single-cell suspension and are then cultivated in several steps. After cultivation, the cells are applied to a gauze surface which is then placed on the prepared burn areas. Skin of originally 2 cm2 in size can be increased to a 10,000 times larger surface over a period of 3 to 4 weeks with about 60 to 80% of the cultivated skin showing accretion. This technique allows for reconstruction of more than half of the body surface [144], [145].

6.2 Stimulation of wound healing through growth factors

Growth factors enhance natural wound healing and thus may be used to support surgical treatment. The recognition of a recombinant growth factor as a product for promotion of wound healing by the Food and Drug Administration (FDA) in 1998 has marked the beginning of a new era in the treatment of chronic wounds [146]].

The main indication for application of recombinant growth factor PDGF-BB (platelet derived growth factor-BB) becaplermin (Regranex®) are chronic crural ulcers in diabetic patients. However, becaplermin can also be used in the facial area. For many other growth factors (transforming growth factor-β [TGF-β], insulin growth factor-1 [IGF-1], fibroblast growth factor-2 [FGF-2]), animal studies have been completed successfully, and additional studies are being prepared [147].

Instead of growth factors, their encoding genes can be introduced into target cells. This occurs via viral or nonviral vectors. Further options include direct intracellular injection of minute microspheres covered with DNA as well as electroporation. In this procedure, an electrode is applied intracutaneously or on the wound surface. Permeability of the cell membrane is increased through electrical current which allows for introduction of DNA from the intracellular area. At present, genetic codes for TGF-β (transforming growth factor-β), PDGF (platelet derived growth factor), and FGF (fibroblast growth factor) have been deciphered. Codes for TGF-α (transforming growth factor-α), VEGF (vascular endothelial growth factor) and IGF (Insulin Growth Factor) are being investigated. In the future, genetic therapy might be used pre-, intra- and postoperatively in order to stimulate respective growth factors in the different phases and at the correct point of time [148], [149], [150].


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