Non-ablative skin tightening
Non-ablative skin tightening modalities can be broadly divided into radiofrequency devices and ultrasound-based devices. Radiofrequency has been around for more than a decade and has a number of variations in terms of energy delivery and efficacy. Radiofrequency is based upon delivery of an electric current through charged particles flowing through a tissue of specific impedance (resistance). Energy output is thermal in origin and is dependent on the amount of current delivered, the length of time of delivery of this current, as well as the impedance (Lolis and Goldberg, 2012). Radiofrequency devices can be monopolar, bipolar or unipolar.
Monopolar radiofrequency devices consist of an electrode and a grounding pad attached to the patient. Some devices have a built in cooling spray around the electrode to prevent superficial heat damage and deliver heat specifically to the dermis initiating the processes of collagen denaturation, disruption of fibrous septae followed by neocollagenesis and shrinkage of fibrous septae. The electrodes disperse their energy in a uniform manner thanks to capacitance coupling. Exact temperatures vary across devices, but in general, the dermis heats up to around 65–75oC with the epidermis maintained at around 35–45o C thanks to the built-in cooling spray.
Zelickson et al examined punch biopsy samples of abdominal skin treated with monopolar radiofrequency (Thermacool, Thermage) immediately after treatment and at intervals of 3 weeks and 8 weeks (Zelickson et al, 2004). At 8 weeks, the authors identified collagen fibrils with a greater diameter, shortening of collagen fibres and an overall increase in collagen. El-Domyati et al replicated these results in the face through biopsy samples taken immediately after facial treatment with a monopolar radiofrequency device, as well as 3 months later (El-Domyati et al, 2011). Similarly, there was evidence of increased collagen formation, as well as a thickened epidermis (El-Domyati et al, 2011). Objective skin tightening effects of these histological changes were demonstrated through brow elevation achieved at intervals following forehead treatment with Thermacool. Recorded complications included short-term erythema and oedema, as well pain and discomfort during the procedure. Indeed, it was clearly noted that as the energy per pass increased, there was increased pain (El-Domyati et al, 2011).
Bipolar radiofrequency consists of two electrodes placed close to each other with an electric current passing between them. There is no grounding plate, and a cooling spray is not required. Bipolar radiofrequency results in heat energy that penetrates to a lower depth as compared with monopolar radiofrequency (El-Domyati et al, 2011). Indeed, the depth of penetration can be derived from half the distance between the electrodes (El-Domyati et al, 2011). However, there is better distribution of the energy, as well as less pain (El-Domyati et al, 2011).
Bipolar radiofrequency is sometimes combined with other forms of light energy, such as intense pulsed light (IPL). The net effect of this is that tissues are pre-treated with the light-based modality, resulting in photothermolysis and a reduction in tissue impedance. Subsequently, there is better absorption of the bipolar radiofrequency energy and hence improved effect (El-Domyati et al, 2011).
Sadick et al published the results of 188 patients treated with the Aurora (Syneron) system (bipolar radiofrequency), and demonstrated a skin laxity improvement of 62.9% (Sadick et al, 2005). Further histological analysis revealed an increase in epidermal thickness alongside a reduction in elastin and increase in collagen. One of the most well-known bipolar radiofrequency devices on the market is the VelaSmooth device (Syneron Candela), incorporating electro-optical synergy (ELOS) technology—a combination of infra-red light and bipolar radiofrequency energy with vacuum cups between the electrodes. This system was developed for the treatment of fibrodysplasia (cellulite). Khan et al (2010) demonstrated a statistically significant decrease in thigh circumference at 4 weeks post VelaSmooth treatment, alongside at least 50% improvement in cellulite at 8 weeks (Khan et al, 2010). A noticeable skin tightening effect was also recorded. Syneron Candela has now launched the VelaShape—a high power device (with 50 W of radiofrequency compared with VelaSmooth’s 20 W), which claims to enable quicker treatments and results.
Further innovation of radiofrequency-based devices has come in the form of fractionated bipolar devices incorporating a microneedle-type probe. Following treatment, columns of heat energy-treated tissue are separated by unaffected columns of tissue that are considered to act as a break between treated areas, as well as a reservoir of cells that promote and accelerate wound healing. This is a similar concept to fractionated ablative and non-ablative laser devices.
Ultrasound-based devices have developed alongside radiofrequency. Ultrasound based energy devices have a lipolytic effect, as well as a skin tightening effect, and this is dependent upon their depth of action. High intensity focused ultrasound (HIFU) and microfocused ultrasound (MFU) deliver thermal energy to the dermis and subdermal layers, resulting in a skin tightening effect. When delivered to depths below the subdermal layer and within the adipocytes themselves, they have a lipolytic effect and can result in fat reduction (Pritzker et al, 2014).
One example of a HIFU device, the Liposonix system (Valeant Pharmaceuticals), operates at a frequency of 2 MHz, delivering 1000 W/cm2 amounting to 100 J/cm2 of energy, resulting in heating to 55oC (Sklar et al, 2014). HIFU is specifically adept at fat reduction and results in fat necrosis with sparing of surrounding tissues treating to a depth of 1.3 cm (Sadick, 2016). With HIFU specifically, the mode of action is that the ultrasound is delivered to a focal point, which determines the depth of action, and therefore the outcome. The user therefore needs to have a thorough understanding of the anatomy of the treatment site to ensure that the energy is delivered to the appropriate depth by altering the focal point. Training is therefore essential.
MFU is more commonly used in skin tightening (MacGregor and Tanzi, 2013). MFU delivers thermal energy to a depth of 5 mm, resulting in temperatures of around 60oC and has been US Food and Drug Administration (FDA) approved as a skin tightening technique for the face, neck and décolletage. Ultrasound is delivered in short pulses and at a higher frequency in MFU treatment, amounting to 0.5–10 J/cm2 of energy to the more superficial dermal subdermal interface, as well as the fibrous septae (Sklar et al, 2014). One variation of MFU is MFU-V, in which visual ultrasound screening is combined with MFU to provide the user with visualisation of the subcutaneous structures to a depth of 8 mm.
Ulthera (Merz) is a MFU device that was specifically developed for skin tightening and lifting of submental tissues and the neck region. It has received FDA approval for this. Ulthera is able to target down to the superficial musculoaponeurotic system (SMAS) layer and creates a 1 mm zone of coagulation. White et al (2007) first demonstrated the formation of discrete and reproducible zones of thermal injury and collagen denaturation in the SMAS using the Ulthera device (White et al, 2007). They used two frequency settings of 9.5 MHz and 4.4 MHz at a fixed focal depth of 4.5 mm with an energy setting ranging from 0.5–8.0 J/cm2. They also identified that the higher the energy setting, the greater the degree of shrinkage; however, this had to be offset against increased amount of pain (White et al, 2007). Alam et al reported the results of Ulthera use in 35 patients (Alam et al, 2010). They reported an average brow elevation of 1.7 mm to 1.9 mm (comparable to reported results with monopolar and bipolar radiofrequency energy devices).
Saket et al (2017) conducted a retrospective review of 22 women, aged between 35 and 65 years of age, who received HIFU treatment to the face and neck for improved lift and skin tightening (Saket et al, 2017). They objectively assessed results using a specific skin laxity measuring tool and demonstrated an average improvement in skin laxity of 58–60%. This was alongside relatively few side effects (Saket et al, 2017). However, this modality causes fat loss and therefore should be used in caution on faces where volume loss is already contributing to an ageing effect. In this situation, fat reduction can cause further volume loss that is not necessarily compensated for by the relative improvement in skin laxity, giving a worse overall appearance. For this reason, effective patient selection is crucial.