From Theory to Technical Excellence: Implementing Microinjections and Cannula Injections into Practice
To see the full video demonstration or to access the slide presentation and additional resources, please visit ReachMD.com/AestheticInjections.
Changes associated with aging skin lead to changes in appearance that cause distress to many women and men, and lead them to seek aesthetic treatment. Fortunately, an increased understanding of the underlying pathophysiologic changes has led to development of aesthetic agents that target underlying mechanisms and injection techniques that result in a natural, balanced, and pleasing appearance.
The aims of this article are to summarize best practices for product selection and injection of hyaluronic acid fillers to optimize aesthetic outcomes and minimize the risk for adverse events. The faculty for the program includes experts in advanced aesthetic techniques. This educational program will review key information about facial and vascular anatomy, selection of the most appropriate hyaluronic acid product based on rheology and physical properties, and advanced injection techniques using both a needle and a blunt-tip cannula.
The goals of treatment with hyaluronic acid
The goals of treatment are to increase the skin elasticity, to create a positive impact on skin surface roughness, and to enhance biosynthesis of new dermal compounds. [Kerscher 2008; Landau 2015]
Hyaluronic acid is a naturally occurring substance that is found in the skin. When injected as a dermal filler, hyaluronic acid stimulates cellular and molecular changes in the skin. A recent study in an animal model showed that hyaluronic acid fillers resulted in a consistent increase in dermal thickness over a 12-week period and the effects lasted up to 24 months. [Kerscher 2008; Landau 2015; Paliwal 2014] In the animal model, the hyaluronic filler was incorporated into the collagen matrix, leading to growth of both smooth compact collagen and loose fibrils, incorporating into the areas of filler placement. Elastin was also present in the location where the hyaluronic acid was injected. [Paliwal 2014]
Hyaluronic acid can be injected using microinjection or blunt cannula techniques. When performing microinjection or blunt cannula injections, best practices include careful attention to facial anatomy, musculature, and neurovascular bundles; selection of product and injection technique; and incorporation of anesthesia and sterile measures. A careful facial analysis is critical to determine realistic treatment goals and to develop a comprehensive treatment approach, including selection of the most appropriate hyaluronic acid formulations based on product characteristics and patient factors. For example, in the lower face, the key to optimizing outcomes is maintaining balance. Facial balance should be considered from the anterior and frontal views as well as the lateral view and chin, which are often ignored. [de Maio 2017a; de Maio 2017b]
Selecting the right product for the right indication is critical for optimal results and it also minimizes the risk for complications. In addition to patient goals, the location of the injection and skin quality should be considered. The most appropriate hyaluronic acid product can then be selected based on rheology and physical properties. It is particularly important to consider the hardness of the gel, referred to as the G-complex, the elastic modulus or G prime, which is the ability of a gel to resist deformation, and also other factors such as the cohesive nature of the gel, the hyaluronic acid concentration, and the degree of crosslinking. Another way to think of G prime is in the context of the elasticity of the filler. For example, a high G prime product is very firm, resistant, and good at lifting. In contrast, a hyaluronic acid filler that has a higher G double prime, the viscous modulus, will be more viscous in nature and therefore is appropriately placed more superficially to “meld” into superficial wrinkles. [Pierre 2015] Other factors to consider include the density, the duration of activity, and the indications approved by the United States Food and Drug Administration. [Landau 2015; Signorini 2016; Costa 2016; US FDA]
Adapted from Costa CR, et al. Plast Reconstr Surg. 2016;138:233e; Bogdan Allemann A, et al. Clin Interv Aging. 2008;3(4):629-634; US Food and Drug Administration. Approved Dermal Fillers; Available at: https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/CosmeticDevices/WrinkleFillers/ucm227749.htm#approved; Bloom M and Palm M. 2018 personal communication.
Only one agent is currently FDA approved for blunt-tip cannula injection. It is small particle hyaluronic acid with lidocaine filler, specifically indicated for lip injection. In the pivotal trial, investigators and subjects reported improvement in lip fullness using the Global Aesthetic Improvement Scale (GAIS) and the Medicis Lip Fullness Scale (MLFS) at 4 and 12 weeks. Importantly, treatment-emergent adverse events were mild and transient, and included injection site swelling (13.3%), injection site bruising (6.7%), and injection site pain (1.7%). There were no serious adverse events following treatment. [Chopra 2018]
Considerations with blunt-tip cannulas
Use of a blunt-tip microcannula is an advanced technique that allows clinicians to achieve the best outcomes with the least amount of trauma for their patients. Sharp needle injections are more likely associated with intravascular embolization. The hypothesis is that direct injection of a needle provides a path of least resistance where the filler can backflow through the entrance point. As the needle advances to the periosteum, it hits the artery, pushing it down to the bone, and penetrates the arterial wall. In contrast, a cannula has more of a sloped angle, creating a more difficult path for the filler to follow to extravasate and be distributed outside the desired area. Other advantages of using cannulas for aesthetic injections include [van Loghem 2016; Fulton 2012]:
A single point of entry allows injection of multiple different areas of the face
Shearing of the cannula through the tissue stimulates fibroblasts to produce collagen
Less pain and virtually no bruising
Minimal patient downtime
Lower risk for intravascular injection and a reduced risk for associated adverse events
In addition, blunt-tip cannula injections lead to more precise placement of the product in targeted anatomical compartments. A recent cadaver study compared needle injection with blunt-tip cannula injection of a yellow dye for temporal hollow and tear trough. Dissection after needle injection showed periosteal and super-periosteal dye as expected; however, dye was present in all tissue layers, including intramuscular and subcutaneous layers. With a cannula, the filler was placed precisely in the desired location with none present in the subcutaneous or intramuscular spaces. Precise filler placement is important, specifically for the tear trough area, which is a challenging area for even the most advanced injectors. The product should be placed deep underneath the orbicularis muscle in order to act as padding so it is not visible superficially. [van Loghem 2016]
Choosing the most appropriate cannula for the chosen product and area to be injected must be given careful consideration. Delicate tissues (ie, lips and the tear troughs), require a smaller cannula (eg, a 27-gauge cannula). More robust tissues, such as the midface, melolabial folds, nasolabial folds, and hands, require a larger-gauge cannula (eg, a 25-gauge, 1.5 inch long cannula) in order to accommodate products with higher viscosity and allow for threading through thicker tissues.
Injection techniques and location of injections compared with the vascular and neurovascular anatomy are of paramount importance to minimize adverse events.
When performing microinjections, injection techniques include linear threading, crosshatching, fanning, serial puncture, or even a combination of several of them, depending on expected results, in order to receive an optimal result. [Landau 2015] NOTE: It is very important to watch the videos demonstrating the injection techniques – the best practices for each injection area are summarized below. Although the demonstrations were performed using the non-animal stabilized hyaluronic acid (NASHA) line of products, one can use any FDA-approved product with similar physical properties (Table A).
Cannula injection of the tear trough: The ideal filler has a low level of hyaluronic acid crosslinking. Create an entry port with a 25-gauge sharp needle based on a diagonal line at a point on the anterior cheek. Use a 27-gauge, 1.5-inch cannula. Insert the cannula below the level of the orbicularis oculi muscle, advancing the cannula perpendicular to the tissue.
Cannula injection of the mid-face and cheek: Ideal fillers are a combination of a hyaluronic acid with a high G prime (eg, a large particle hyaluronic acid) and a different product with a good combination of support and flexibility. Create a pilot hole with a 23-gauge sharp needle and use a 25-gauge, 1.5-inch microcannula for the injections, using a lift and tack or layered lifting technique. Inject about 2/3 of the product onto the periosteum of the midface and about 1/3 of each aliquot coming up through the deep fat pads and into the superficial fat pads. Create another pilot hole in the area that was previously injected and use a 25-gauge, 1.5-inch microcannula for the midface volumization, using a radial threading technique to treat the anterior midface.
Cannula injection of the lips: A small particle hyaluronic acid filler with lidocaine is the only FDA-approved product for injection in the lip area with a microcannula. Four important factors to consider are: 1) the definition of the vermillion border; 2) the fullness of the lips; 3) the pout; and 4) the proportion of the top and lower lips. Create a pilot opening at the corner of the mouth with a 25-gauge needle to be used with a 27-gauge, 1.5-inch microcannula. Inject 0.1 to 0.2 mL of filler in each of the four quadrants (pillows) of the lip. Next, angle the cannula into the top lip in the submucosal plane to inject first into the dry red lip, then aim into the mouth at the wet-dry border and even more posterior or lingual to that in order to push or roll the lip out. Repeat this technique for the other side. Use the sharp needle to give more definition to the top lip at the vermilion border in the lateral Cupid’s bow. One can complete this area by injecting the marionette area with a 30-gauge needle. Begin with the pillar of the marionette area and inject very slowly using very small quantities of product, working from the jaw line up to the oral commissure.
Microinjection of the forehead: The filler (small particle hyaluronic acid with lidocaine) is mixed with 0.3 to 0.5 cc of 0.5% lidocaine with epinephrine buffered with bicarbonate in a 0.3 cc syringe, and is ideal for the forehead as it provides a thinner product that is more easily molded into thinner tissues. Inject at least 1 cm above the orbital rim because it is a safe place that is super-periosteal on top of bone and below the area where important vessels are located. Inject down to bone on the super-periosteum and march over laterally going very slowly and using small aliquots. Finish laterally, injecting perpendicular to the surface of the skin.
Microinjection of the neck: The filler is mixed with 0.5% lidocaine with epinephrine buffered with bicarbonate for vasoconstrictive effect and to minimize the degree of swelling and bruising. A sharp needle is the only appropriate approach for placing filler in the neckline. Bending the needle allows for a tangential approach while working from the right side of the neck. Inject in an anterograde and retrograde linear threading pattern to subcise and fill the neck lines.
Minimizing adverse events
When performing microinjections or blunt cannula injection of hyaluronic acid, prevention and management of adverse events must always be top of mind. Safety techniques include aspiration after insertion to ensure the needle/cannula is not in a vessel and injection of small, precise aliquots at a slow rate. If resistance is encountered and/or the patient experiences pain, the injector should stop and reposition the cannula or needle prior to injecting more filler. [Signorini 2016; Beleznay 2015]. Interaction between the hyaluronic acid fillers and the tissues may cause immune-mediated and delayed-type hypersensitivity reactions. Patient monitoring after the injection (blanching or other warning signs) can facilitate prompt management.
A safety kit containing hyaluronidase should always be available to treat emergent vascular complications. The central part of the face, including the nose and mid-cheeks, is particularly important because of the anastomosis between internal and external carotid vasculature; accidental injection of hyaluronic acid in these vessels may lead to necrosis or blindness, which is the most feared complication of hyaluronic acid filler injection. A recent worldwide review of 98 cases of blindness over the past several decades revealed that the majority occurred in the central face. Although most cases were related to autologous fat injection, every filler product that is currently FDA approved was represented in the study. Most cases of blindness are permanent, although there are emergent cases that have reversal and restoration of visual acuity and include retrobulbar injections or pulsed intra-arterial hyaluronidase injections. [Beleznay 2015]
Full correction requires several sessions. After results are achieved, patients should be reassessed every 3-6 months. Treatment touch-ups usually occur at a frequency of about every 6-9 months.
Hyaluronic acid fillers have gained popularity in recent years. To achieve naturally appearing results and minimize the risk for adverse events, it is important to gain mutual agreement on realistic treatment goals, select the most appropriate fillers based on an understanding of physical properties and rheologic characteristics, and follow meticulous advanced injection techniques. Patient education to clearly set expectations about post-injection care, timelines required to see optimal results, and the need for repeat injections is also important to optimize patient satisfaction, safety, and outcomes.
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Chopra J, et al. J Drugs Dermatol. 2018;17(1):10-16.
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Fulton J, et al. J Drugs Dermatol. 2012;11(9):1098-1103.
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US Food and Drug Administration. Approved Dermal Fillers. Available at: https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/CosmeticDevices/WrinkleFillers/ucm227749.htm#approved. Accessed April 9, 2018.
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