By Amber Luong, MD/PhD
Once sought in secrecy, cosmetic procedures are enjoying greater public acceptance. Reported by the American Academy of Facial Plastics and Reconstructive Surgery (AAFPRS), there have been a 60 percent increase in men and a 30 percent increase in women undergoing cosmetic procedures since 2000 (AAFPRS, 2006). Although facelift procedures continue to be popular, less invasive techniques addressing wrinkles such as laser resurfacing, chemical peels and Botox injections have seen continued increase in numbers.
Important Anatomy
Skin Anatomy
The skin is the largest organ of the human body and serves as the primary barrier from the environment. It consists of two layers, the epidermis and the dermis layer, which lie on the subcutaneous fatty tissue. The epidermis is the outer layer and is a stratified squamous epithelium. Its thickness ranges from 0.05 mm over the eyelid to 1.5 mm over the palms and soles.
The epidermis consists of 5 layers, each layer characterized by keratinocytes at different stages of differentiation. The inner most layer, the stratum basale is formed by a single layer of keratinocytes that are attached to the basement membrane by hemidesmosomes. This layer also contains the melanocytes that make melanin. Newly created keratinocytes differentiate and move from inner to outer layers. In this same orientation, the layers are stratum spinosum, stratum granulosum and stratum corneum. The flattened, fully differentiated keratinocytes, which make up the stratum corneum, are devoid of a nucleus and ultimately are shedded.
In addition to the keratinocytes, other specialized cells are also found within the epidermis. Langerhan cells are antigen-presenting cells and are found thoughout the epidemis. Melanocytes, found primarily in the stratum basale, are responsible for the melanin production. Finally, Merkel cells are located in this layer. Derived from neural crest cells, Merkel cells function in light tough perception.
The dermis lies deep to the epidermis and ranges in thickness from 0.3mm on the eyelid to 3.0mm on the back. Although consisting of only 2 layers, the dermis is more complex than the epidermis. The more superficial and thinner layer, the papillary dermis and is composed of loosely organized collagen, elastin fibers, reticular fibers and capillaries. Deep to this layer resides the reticular dermis that consists of collagen arranged in bundles parallel to the surface, tightly interlaced elastic fibers and large vessels. In addition, the dermis includes lymphatics, mast cells, nerve endings and epidermal appendages. The dermis provides the support for the overlying epidermis.
Superficial Musculoaponeurotic System (SMAS)
The superficial musculoaponeurotic system (SMAS) is a fibromuscular layer which envelopes the mimetic muscles of the face and neck. Described by Mitz and Peyronie in 1976, the SMAS inferiorly it is contiguous with the playsma and superiorly with the galea and the superficial layer of the temporalis fascia (Mitz and Peyronie, 1976). The superficial layer of the temporalis fascia is also referred to as the temporofascial layer. At the zygomatic arch, the SMAS is continuous with the periosteum. Medially, the SMAS thins into the nasolabial fold and has cutaneous attachments. It lies just superficial to the parotid fascia. It is a critical structure to understand because of its role in rhytidectomy.
Facial Nerve
The facial nerve exits the stylomastoid foramen and courses superiorly to enter the parotid gland. Within the gland, the nerve divides into the temporofascial and the cervicofacial branches. These main branches ultimately arborize into 5 named branches: cervical, marginal mandibular, zygomatic, buccal, and temporal. The nerve divides the gland into a superifical and deep lobe. For the most part, the nerve is deep to the SMAS layer. However, medial to the anterior edge of the parotid gland, the branches of the nerve emerge from the gland, putting them at risk to injury.
Retaining Ligaments
The retaining ligaments of the face serve to anchor the skin to the underlying bony structure. Furnas described 4 retaining ligaments (Furnas, 1989). Two important osteocutaneous ligaments are the mandibular and the zygomatic ligaments. They support the facial structures and skin against the gravitational pull. The other two ligaments, the platysma-cutaneous and platysma-auricular ligaments are aponeurotic condensations attaching the platysma to the overlying dermis. These ligaments have to be released during rhytidectomy in order to mobilize and to resuspend the facial structures.
Histologic and Facial Characteristic Changes in the Aging Face
Effects of Aging on Facial Skin
Aging ultimately is a process resulting in atrophy and disorganization of both the epidermal and dermal layers. Specifically, the number of melanocytes decreases with age resulting in hypopigmetation. The rete ridges flatten within the dermal-epidermal junction, which results in fragility of the skin. The proliferative capacity of the keratinocytes and fibroblast decreases resulting in thinning of the epidermal and dermal layers. The production of collagen and the ratio of Type I to Type III collagen decreases, both causing a disorganized and weakened dermal layer. In addition, the connective tissue supporting the blood vessels weakens, that leads to the ease of bruising in the older population. Ultimately, aging results in atrophy and weakening of the skin.
Sun Exposure Effect on Facial Skin
Although both aging and sun exposure cause undesired changes to the skin, the histological changes from photo damage is unique from aging. In general, rather tan causing atrophy, sun damage results in formation of excess, poorly elastic, thickened skin. The denaturization of cutaneous elastin proteins causes deposition of nonelastic tangled masses, which result in poorly elastic excess skin. Ultraviolet wavelengths also cause actinic damage and dermal elastosis. This results in the thickened, leather-hide like skin. In addition, sun exposure results in proliferation of melanocytes and hyperpigmenation.
Both aging and environmental stresses, with sun exposure being the most common damaging agent, cumulatively result in formation of rhytids and ptosis of facial skin. A common area of concern is the submental region with loss of the cervicomental angle as a result of laxity of the platysma and the submental skin. Jowling is another concern as the buccal fat and malar skin descend below the mandible. This descend also creates an undesired prominence of the mesolabial fold. A number of facial rejuvenation techniques have been described to address these signs of aging. This paper will only discuss rhytidectomy, chemical peels, dermabrasion and laser resurfacing.
Rhytidectomy
Face-lifts or rhytidectomy are indicated for ptosis of deep anatomical facial structures. Lexar in 1916 is credited with promoting the first traditional rhytidectomy, which consisted of elevating the skin in the subcutaneous plane, lifting the skin taut vertically and excising the excess amount. Long-term results were limited and this surgical approach prevented significant changes in the mid face. In 1968, Skoog began elevating the platysma and the skin superficial to this level (Skoog, 1969). Mitz and Peyronie (1976) detailed this significant advancement by defining the SMAS layer (Mitz and Peyronie, 1976). This fundamental change was heralded with improvement in long-term changes and minimizing the stigmata of face-lift surgery.
The SMAS rhytidectomy entails an incision that starts in the temporal region paralleling the hairline. As the incision proceeds inferiorly, it is placed in the preauricular crease. In females, this incision is often placed behind the tragus. Then, the incision follows the lobule margin posteriorly and continues post-auricular superiorly within the posterior sulcus. The incision is often taken into the hairline and then curves posteriorly onto the mastoid. A subcutaneous flap is elevated creating a 4-5 centimeter flap, exposing the SMAS. The SMAS is then suspended in a vertical and lateral vector with sutures.
Despite the improved results, the midface remained poorly affected by the SMAS rhytidectomy. Deepening of the mesolabial folds, associated with the aging face, results from ptosis of the malar fat pad. As the malar fat is attached to the underlying zygomatic muscles that are tethered to the bony structure, suspension of the overlying SMAS and skin understandably has minimal short-lived effects on the midface. To address this shortcoming, Hamra proposed the deep-plane rhytidectomy to focus on the melolabial fold and malar region (Hamra, 1990). This surgical technique involves the traditional elevation of a subcutaneous flap first, which again exposes the SMAS. In the deep-plane rhytidectomy, the deep plane dissection is entered just anterior to the line extending from the angle of the mandible and the junction of the zygomatic arch and the malar eminence. The dissection continues medially past the nasolabial fold just on the superficial aspect of the underlying facial muscles, completely releasing all the SMAS attachments. The resulting flap contains the platysma, the skin and most importantly the malar fat pad. The deep-plane rhytidectomy aims to address the midface and mesolabial fold. Theoretically, the disadvantage with this approach is increase risk of injury to the branches of the facial nerve as they emerge from the protection of the parotid gland. However, Hamra reports that the complication rate is comparable to that of the SMAS rhytidectomy.
For comparison, the SMAS rhytidectomy that preceded the deep-plane rhytidectomy suspends the SMAS and platysma but does not include dissecting to the mesolabial fold. In a study by Kamer and Frankel (Kamer and Frankel, 1998), the deep-plane rhytidectomy was objectively compared with the SMAS rhytidectomy in terms of need for a revision tuck procedure. They found that patients undergoing the SMAS rhytidectomy had a significantly higher incidence of tuck procedures (11%) as compared to patients who underwent the deep-plane rhytidectomy (3%). However, in 2004, Becker and Bassichis subjectively compared the SMAS and the deep-plane rhytidectomy. Using 4 facial plastic surgeons to rate the post-operative pictures of patients undergoing one of the above approaches, they found that for patients under the age of 70 had more post-operative results rated as "excellent" when undergoing a SMAS approach versus a deep-plane approach. The deep-plane approach had better results as compared to the SMAS approach in only a select small group of patients older than 70 years of age (Becker and Bassichis, 2004).
Given the variations in patients' desired results and the number of different facial surgical zones, a number of different techniques have been introduced. The composite rhytidectomy was introduced as a combination of the deep-plane rhytidectomy with a component to address ptosis of lower orbicularis region. Another approach, the subperiosteal rhytidectomy consists of a plane of dissection deep to the mimetic facial muscles, releasing them from the underlying bony attachment. These different techniques claim more dramatic effects and improved attention to areas such as the midface that are not affected significantly by the traditional rhytidectomy.
Complications
The most common complication from a rhytidectomy is a hematoma, approximately 10% rate. It presents as rapidly enlarging swelling of the face associated with pain. This is a significant complication that can cause necrosis of the facial flap if not evacuated in a timely fashion.
Damage to nerves can be a devastating complication, with sensory nerves more often injured than motor nerves. The most common sensory nerve injured is the greater auricular nerve. The most common motor nerve injured is the marginal mandibular nerve.
Another common complication of rhytidectomies is necrosis of the retroauricular skin flap. This can be avoided by keeping a broad base on the retroauricular skin flap.
Some uncommon complications to be aware of are severe edema, infection and skin changes such as scaring or hyperpigmentation.
Chemical Peels
The use of chemical peels for facial rejuvenation dates back to the Egyptian times. Used by Cleopatra for her skin regimen, lactic acid was the original chemoexfoliant. This practice was continued into the Middle Ages where sour milk was the source of the lactic acid. In the 1920s, Sir Harold Gillies used pure carbolic acid to correct the eyelid laxity. Croton oil, which is a component of Baker's solution used in deep peels, was isolated from croton resin in 1935. In the 1940's, the lay peelers popularized chemical peels starting with a mixture of resorcinol and salicylic acid for superficial exfoliation. Additional experimentation with formulations generated the mixture currently known as the Baker's solution for deep peels, which includes phenol, septisol and croton oil. Chemical peels are classified by the depth of the peel. Superficial peels are limited to the epidermis. A number of agents are available for superficial peels including the family of alpha hydroxy acids and salicylic acids. Driven by the interest in skin rejuvenation, many cosmetic products contain one of these chemoexfoliant agents.
Alphy hydroxy acids (AHA) include lactic acid, glycolic acid and pyruvic acid. These are naturally occurring weak acids that are naturally found in foods. For peels, concentrations typically range between 50 and 70 percent. Applied topically, AHA cause epidermolysis by chelating calcium ions that are important in desmosome function. The interruption of cell-cell tight junctions results in the sloughing of keratinocytes, which stimulates production of new cells at the basal layer in the basal cells (Wang, 1999). The advantages of AHA are minimal "downtime" and little effect on daily activities, no requirement of sedation or anesthesia, and low cost. However, the effects are less dramatic compared to the deeper peels. In addition, multiple applications are required for effect.
Salicylic acid is another common agent for superficial peels. Used at 20-30% concentration, salicylic acid is lipophilic which enhances penetration. Salicylic acid also has anti-inflammatory properties. These two characteristics have been utilized for treatment of comedones. Salicylic acid is combined with resorcinol and lactic acid to form Jessner's solution, which is commonly used in superficial peels.
Trichloroacetic acid (TCA) is a keratocoagulant used for intermediate to deep peels. Concentrations used range from 20 to 50 percent, with the higher concentrations resulting in a deeper penetration and peel. The incited wound healing results in increased amounts of type I and III collagen and elastic fibers. In addition, there is significant increase in the thickness of the epidermal layer (El-Domyati et al., 2004). Once used as a single agent for deep peels, 50% TCA as a single agent has been replaced with combination therapy coupled with 35% TCA. The primary disadvantage of TCA at this high concentration is risk of scarring. One such combined therapy is solid CO2 applied prior to application of 35% TCA. The solid CO2 appears to weaken the epidermal layer allowing more effective penetration of the TCA with the decrease risk of scarring (Brody, 1989).
Deep peels are characterized by penetration to the reticular dermis. As a result, deep peels are more effective than the superficial peels at treating deep rhytids and actinic damage. However, there is an associated increase risk of scarring, especially for Fitzpatrick IV-V skins. Phenol is the primary agent used in deep peels, either as a single agent or in a solution such as the Baker-Gordon formula. Concentrations used for deep peels ranges from 50% to 88%. Clinical experience with phenol established the long held dogma that the lower concentrations result in a deeper peel. The higher concentrations result in immediate coagulation of epidermal proteins creating a barrier to penetration. Hetter (2000) challenged this dogma recently by showing that phenol without croton oil resulted in a skin reaction without epidermolysis. Rather, the depth of peel was dependent on the concentration of the croton oil. He suggested that the dogma was established by erroneously assuming that the phenol was the peeling agent. He argues that phenol acts as the carrier agent for the croton oil (Hetter, 2000).
Cardiac toxicity is the primary concern with the use of phenol. Phenol is metabolized by the liver and excreted through the kidneys. Toxicity can result in arrhythmias and myocardial irritability. Consequently, to minimize risk of cardiac toxicity, the face should be divided into quadrants and treated in segments. In each segment, less than 25% of the face should be treated with each treatment segment separated by 15 to 20 minutes. In addition, intravenous hydration should be given prior to and during the procedure. Finally, telemetry monitoring is important during and after the procedure.
Complications associated with chemical peels can often be avoided by selecting the appropriate depth of peel for the skin type. Fitzpatrick skin types IV through VI are prone to pigmentary changes after chemical peels. Therefore, these skin types should be counseled about the risk with chemical peels and deep peels should be avoided. Also, patients with a history of scaring or keloids should not undergo medium or deep peels. The appropriate selection of chemical peel depth for each skin type can prevent many complications.
Laser Resurfacing
Laser resurfacing was introduced in the 1963 by Goldman when he applied lasers for cosmetic procedures. The most common laser used initially was the CO2 laser. Since then, the erbium:Yttrium-aluminum-garnet (Er:YAG) laser has been introduced and is now widely used for laser resurfacing. Both these lasers are categorized as ablative lasers because they incite damage and exfoliation of the epidermis. Clinically, patients experience erythema of the skin, which require several days to heal. On the other hand, a new class of lasers has been introduced that are classified as non-ablative. These lasers (e.g., visible light lasers) are absorbed by specific molecules within the skin rather than directly damaging the epidermis. As a result, the healing time is significantly lessened with these non-ablative lasers.
The CO2 laser has a wavelength of 10600 nm. It was initially delivered as a continuous wave but this delivery system resulted in significant wound healing time. The delivery was revised to a high-powered pulsed system. The pulsed CO2 laser shows similar dramatic facial changes with more controlled and less epidermal damage as compared to the continuous CO2 laser. The extent of tissue ablation is 50 to 100 µm with a 30 to 50 µm of thermal conduction to the surrounding tissue. Subsequent passes may increase the extent of tissue ablation up to 200 µm, but the area of thermal conduction also increases up to 150 µm. Re-epithelialization takes 10 to 14 days with residual erythema lasting 3 to 6 months. This length of healing time is the primary disadvantage of the CO2 laser.
The Er:YAG emits a wavelength of 2940 nm which is absorbed more readily by water than that of the CO2 laser. This clinically translates into more superficial penetration. In addition, each pass of the Er:YAG laser causes tissue ablation of 10 to 40 µm but only a 10 to 20 µm zone of thermal conduction. Unlike the CO2 laser, an additional pass with the Er:YAG laser does not increase the area of thermal conduction. Consequently, the time of re-epithelialization is reduced to 4 to 7 days and erythema resolves within 2 to 4 weeks. Compared to the CO2 laser, the Er:YAG causes less thermal damage but has less tissue penetration.
The slight differences in the Er:YAG and CO2 laser have been explored. With the greater tissue penetration, the CO2 laser results in more dramatic clinical changes than the Er:YAG. It is hypothesized that the facial rejuvenation results from the laser disrupting collagen bonds resulting in remodeling of preexisting collagen and deposition of new organized collagen (Rostan, 2005). Millman and Mannor (1999) argued that the combination of the two lasers provided better tissue penetration than Er:YAG laser alone while minimizing the extent of surrounding thermal damage (Millman and Mannor, 1999). There is no consensus as to which laser is more effective and hence both are widely used.
With the healing time associated with ablative lasers, the use of nonablative lasers has increased significantly. There are a number of nonablative lasers available and a discussion of these lasers are outside the realm of this article. Examples of nonablative lasers include the 1320-nm Nd:YAG, 1064-nm Nd:YAG, 1450-nm diode and pulsed-dye laser. The clinical effects are less dramatic than the ablative lasers, but are effective for mild rhytids, mild acne and vascular lesions. The primary advantage of these nonablative lasers is the reduced healing time.
The availability of ablative and nonablative lasers and the more controlled degree of penetration over chemical peels makes laser resurfacing an attractive alternative to patients seeking facial rejuvenation.
Dermabrasion
Dermabrasion is a technique of mechanical removal of the epidermal and part of the dermal layer to incite wound healing. A result of initiating the cascade of wound healing is deposition of new elastin and collagen within the dermal layer. A hand-held motorized device with an abrading end piece is passed horizontally over the treated skin. A number of end pieces are available including a serrated wheel, a diamond fraise or a wire brush. The fraises come in a variety of shapes to accommodate different contours of the face. In addition, different grades of coarseness are available to optimize the degree of penetration. The wire brush requires a spray refrigerant to create a firm frozen surface because it tends to grab loose skin and free edges. The wire brush imparts less thermal injury to the treated skin than the diamond fraise. Dermabrasion is effective in treating uneven scars and removing benign lesions.
Preoperative considerations are similar to those for chemical peels. Antivirals must be initiated prior to the procedure to prevent herpetic outbreaks. In addition, tretinoin cream is started several weeks preoperatively to decrease the time for reepithelization.
The depth of abrasion should not go beyond the dermal layer. Ideally, the abrasion should involve the superficial papillary dermis. Surgically, this layer is characterized by cornrow punctuated bleeding. The deep reticular dermis bleeding is associated with larger punctum and white parallel lines of collagen. Abrading deeper that the dermal layer is associated with scarring.
Unlike chemical peels and laser resurfacing, dermabrasion is not ideal for large surface areas. However, it provides an excellent solution for treatment of uneven scars or small lesions.
Conclusion
There are a number of techniques available for facial rejuvenation. Each has their advantages and disadvantages. Knowledge of these techniques provides a rich armamentarium for facial rejuvenation.
References
American Academy of Facial Plastic and Reconstructive Surgery (2006). 2005 Membership Survey: Trends in Facial Plastics Surgery. http://www.aafprs.org/media/stats_polls/aafprsMedia2006.pdf
Becker, F. F. & Bassichis, B. A. (2004). Deep-plane face-lift vs superficial musculoaponeurotic system plication face-lift: a comparative study. Arch Facial Plast Surg, 6(1), 8-13.
Brody, H. J. (1989). Variations and comparisons in medium-depth chemical peeling. J Dermatol Surg Oncol, 15(9), 953-63.
El-Domyati, M. B., Attia, S. K., Saleh, F. Y., Ahmad, H. M., & Uitto, J. J. (2004). Trichloroacetic acid peeling versus dermabrasion: a histometric, immunohistochemical, and ultrastructural comparison. Dermatol Surg, 30(2 Pt 1), 179-88.
Furnas, D.W. (1989). The retaining ligaments of the cheek. Plast Reconstr Surg, 83(1), 11-16.
Hamra, S. T. (1990). The deep-plane rhytidectomy. Plast Reconstr Surg, 86(1), 53-61; discussion 62-3.
Hetter, G. P. (2000). An examination of the phenol-croton oil peel: part IV. Face peel results with different concentrations of phenol and croton oil. Plast Reconstr Surg, 105(3), 1061-83; discussion 1084-7.
Kamer, F. M. & Frankel, A. S. (1998). SMAS rhytidectomy versus deep plane rhytidectomy: an objective comparison. Plast Reconstr Surg, 102(3), 878-81.
Millman, A. L. & Mannor, G. E. (1999). Combined erbium:YAG and carbon dioxide laser skin resurfacing. Arch Facial Plast Surg, 1(2), 112-6; discussion 117.
Mitz, V. and Peyronie, M. (1976). The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg, 58(1), 80-88.
Rostan, E. F. (2005). Laser treatment of photodamaged skin. Facial Plast Surg, 21(2), 99-109.
Skoog, T. (1969). Useful techniques in facelifting. Paper presented at the Meeting of the American Association of Plastic Surgeons, San Francisco.
Wang, X. (1999). A theory for the mechanism of action of the alpha-hydroxy acids applied to the skin. Med Hypotheses, 53(5), 380-82.
