Radiofrequency Microneedling

Summary and Key Features

• Radiofrequency microneedling is a minimally invasive modality that creates perforations in the skin and delivers radiofrequency-generated thermal energy into the underlying tissue

• The perforations created by microneedles improve transcutaneous absorption of topical products and transcutaneous elimination of skin debris

• The mechanical and thermal effects of radiofrequency microneedling cause dermal coagulation, collagen remodeling, and neoelastogenesis via a wound-healing response

• Dermatologic conditions with numerous high-quality evidence supporting its use include skin rejuvenation, acne scars, acne vulgaris, and axillary hyperhidrosis

• Other potential dermatologic indications include striae, rosacea, androgenetic alopecia, cellulite, and melasma.

• Radiofrequency microneedling is a safe option with low risk of postinflammatory hyperpigmentation, even in individuals with darker skin phototypes

• Radiofrequency microneedling can be safely combined with several other therapeutic modalities to augment clinical outcomes without significant increase in risk of adverse events

Introduction

Radiofrequency devices have been used in the medical field for decades to achieve hemostasis, electrocoagulation, and endovenous closure. Within the realm of esthetic medicine, the first radiofrequency device (ThermaCool, Bausch Medical, Bothell, WA) was approved for the treatment of periocular rhytides in 2002, then facial rhytides in 2004, and subsequently extra-facial sites in 2006. Numerous radiofrequency devices for esthetic purposes have since been approved and utilize various methods of delivering radiofrequency energy to the underlying dermis and subcutis ( Table 12.1 ). Radiofrequency energy can be delivered to the underlying dermis and subcutis via noninvasive probe-based electrodes, or minimally invasive needle-based electrodes. This chapter will focus primarily on the needle-based method, also known as radiofrequency microneedling (RFMN).

Radiofrequency

Radiofrequency energy is within the electromagnetic spectrum with a frequency ranging from 3 kHz to 300 GHz. The typical frequencies used in esthetic medicine is between 0.3 and 10 MHz. Thermal energy is generated from the tissue’s intrinsic resistance, known as impedance, to the movement of electrons within the radiofrequency field. The amount of energy delivered is governed by Ohm’s law and is relative to the amount of current, exposure time and impedance of target tissue (see Box 7.2 ).

Various structures of the skin and the underlying tissue exhibit different impedance (see Table 7.2 ). Tissues with higher impedance, such as muscle, cartilage or wet skin, are more susceptible to heating compared to tissues with lower impedance, such as bone, fat and dry skin. The properties of an individual’s tissue (thickness of skin, fat and fibrous septa, the number and size of adnexal structures) all contribute to impedance, heat perception and total energy deposited. The tissue impedance is further affected by its current temperature and in general, decreases by 2% for every 1°C increase in temperature.

Polarity of Radiofrequency

Radiofrequency energy can be delivered via monopolar or bipolar configuration. In monopolar configuration, current passes from a single electrode in the handpiece to a grounding pad placed on a patient’s distal body part ( Fig. 12.1 ). Monopolar configuration creates a high density of power at the electrode’s surface and has the potential to heat deeper tissues such as the reticular dermis and fibroseptal network ( Fig. 12.2A ). In bipolar configuration, current passes between electrodes within the handpiece ( Fig. 12.2B ). This configuration allows for a more controlled distribution of radiofrequency at a higher energy level, but is more limited in the depth of penetration. Other factors affecting the depth of penetration include the frequency of the electrical current, as well as temperature and types of tissues present.

Collagen Remodeling

The optimal temperature to induce partial dermal collagen denaturation, neocollagenesis and neoelastogenesis is approximately 67°C. Dermal temperatures ≥69.5°C or ≤62°C result in suboptimal clinical efficacy due to overdenaturation and underdenaturation of collagen respectively. The amount of collagen denaturation is determined by a combination of temperature and exposure time ( Fig. 12.3 ). Studies have shown that temperatures ≥85°C are needed when shorter exposure times (<1 second) are used, or temperatures 60°C–65°C are needed when longer exposure times (≥1 second) are used. To achieve the optimal treatment outcome, temperature and impedance of the tissues being treated have to be monitored so that the RFMN device delivers the precise amount of energy. This monitoring occurs via feedback loops within the handpiece and provides real-time feedback to maintain the temperature during the exposure time.

Epidermal Protection

In contrast to the dermis, the critical heat threshold to avoid epidermal burns is 44°C. Therefore overly aggressive treatment of the deeper tissues without proper protection of the overlying epidermis can lead to epidermal burns and complications such as blistering, scarring, and postinflammatory hyperpigmentation (PIH).

Epidermal cooling, in the form of a cryogen spray or contact cooling plate, can be applied to protect the superficial layers of the skin while heating the deeper tissues ( Fig. 12.2A–C ). Epidermal cooling also increases tissue impedance and redirects radiofrequency away from the epidermis. Other methods of minimizing epidermal injury may include constant motion of the handpiece or using insulated microneedles. In RFMN using insulated microneedles, the proximal ends of the needles are insulated, and radiofrequency is delivered only at the distal ends that are embedded in the target tissue ( Figs. 12.2D and 12.4 ). The temperature of the epidermis and dermis can be monitored in real-time by sensors within the handpiece or through infrared cameras.

Radiofrequency Versus Lasers

RFMN differs from ablative lasers in several aspects. Lasers function on the theory of selective photothermolysis, whereby chromophores in the skin have different absorption peaks at different wavelengths of light. Ablative lasers selectively target water as the chromophore and creates a temperature gradient that tends to be highest at the epidermis and decreases as it penetrates the deeper layers of the skin. This thermal injury to the epidermis increases the risk of PIH, especially in patients with darker skin phototypes. In contrast, RFMN is dependent on impedance of the target tissue only and is strictly an electrothermal effect. It is not dependent on skin chromophores, thereby rendering RFMN a “color-blind” technology that is not affected by the amount of melanin present in the skin. Radiofrequency energy is directly delivered to the target depth through the microneedle electrodes, thus creating a temperature gradient that is highest in the deeper structures and cooler at the superficial structures. This results in less epidermal heating and reduces the risk of PIH. Compared to lasers, radiofrequency energy can also be delivered to deeper structures of the skin through increasing the depth of penetration or length of microneedle electrodes.

Characteristics of Microneedles in Radiofrequency Microneedling

The microneedles used in RFMN are wider at the proximal ends connected to the handpiece, and taper to sharp tips at the distal ends to allow for penetration of the skin. They are usually arranged in square arrays of 5 × 5, 6 × 6, or 7 × 7 microneedles, but many other arrangements also exist. The microneedles are delivered to the skin through either mechanical motors, solenoids, or manual operator applications. The length of microneedle and depth of penetration in most modern RFMN devices can be adjusted depending on the indication of treatment ( Fig. 12.5 ). This allows for a more precise targeting of the desired tissue, while avoiding injury to collateral structures. The adjustability is also important given that different anatomic sites have different epidermal and dermal thickness ( Figs. 12.6 and 12.7 ).

An important consideration when deciding on treatment parameters is to note that the desired depth of penetration may not always correspond to the actual depth. In general, the actual depth of penetration tends to be more superficial. Many factors can contribute to this inadvertent targeting of more superficial structures than desired: (1) operator-dependent factors, such as insufficient pressure applied or imprecise holding of the handpiece resulting non-perpendicular contact with the skin; (2) patient-dependent factors, such as thickened or scarred skin is more difficult to penetrate; (3) device-dependent factors, such as an underpowered motors or solenoids, or dull needles from poor manufacturing quality.

The microneedles can be noninsulated or semiinsulated. In RFMN using noninsulated microneedles, radiofrequency energy is delivered along the entire length of the microneedle electrode ( Fig. 12.8 Left). This results in both mechanical and thermal injuries to the epidermis and underlying structures. In RFMN using semiinsulated microneedles, radiofrequency energy is delivered only at the distal end of the microneedle electrode, bypassing the epidermis ( Fig. 12.8 Right). Hence, epidermal injury is limited only to the mechanical perforations and this reduces downtime and patient discomfort. When using more aggressive treatment settings however, some degree of heat can still permeate through the insulation.

In addition to radiofrequency-induced thermal injury, the mechanical effects of microneedles creating perforations in the skin also allow for improved transcutaneous absorption and elimination of topical products and skin debris respectively, and further stimulates the wound-healing response and secretion of growth factors that lead to migration and proliferation of fibroblasts for collagen remodeling, neocollagenesis and neoelastogenesis.

Indications

The most common indications for RFMN are skin rejuvenation, acne scars, acne vulgaris, and axillary hyperhidrosis. Other conditions which may also respond to RFMN include rosacea, male-pattern androgenetic alopecia, and striae. Although RFMN has been successfully used for the treatment of melasma and cellulite, there is still limited evidence to support its use in these conditions.