Filler Injection Techniques

Introduction

The placement of soft tissue fillers can be likened to four-dimensional sculpture, with the fourth dimension representing dynamic movement. With this analogy in mind, rather than a hammer and chisel, an injector’s toolbox includes needles and cannulas. Both art forms involve a few basic techniques that can be combined to lead to a tailored result; instead of casting and modeling, filler injection hinges on techniques like threading and fanning. The artist injector must have a detailed knowledge of anatomical structures, as the appropriate “canvas” or injection plane, changes depending on the anatomic site, injectable material, injection instrument, and desired result. In this chapter, we discuss the instruments used for injection and the fundamental techniques commonly employed to deliver soft tissue filler.

General Injection Principles

Despite a myriad of stylistic approaches, safe and efficacious filler injection rests on a bedrock of good practice principles. Patient selection should ensure that the injection site is free from infection or recent procedures. Even a distant history of surgery, which can lead to vascular aberrancies, should indicate a pause in the procedure, especially in risk-prone sites like the nose. While patients may be fixated on a single fold or wrinkle, the clinician must determine if the requested injection will indeed add harmony to the patient’s appearance. The patient’s desired endpoint may require injection of a different anatomic site or be better achieved using a laser or energy-based modality. Once the patient is deemed an appropriate candidate and a mutual goal is shared by the patient and injector, enthusiastic written and verbal consent should be obtained. In addition to consent, pretreatment photographs not only are informative for the follow-up appointment but also serve as a safeguard in the case of medico-legal issues. The patient should be free of makeup and the skin cleansed with an appropriate antiseptic such as chlorhexidine, isopropyl alcohol, povidone-iodine, or hypochlorous acid solution. The patient should be positioned in a comfortable upright position, with lighting placed in a fashion that properly showcases the defect.

The syringe is often held near the barrel flange between the second and third fingers of the dominant hand, with the first digit in contact with the plunger thumb rest. Adducting the arms toward the trunk and resting the injecting hand on the nondominant hand minimize additional pivot points, so that movement is limited to the dexterous joints of the injecting hand ( Video 32.1 ). Sometimes, the skin surrounding the injecting site may need to be stretched or pressure must be applied to surrounding vascular structures, and in these situations, the extra hands of a trained assistant are invaluable.

Prior to filler injection, aspiration is a maneuver that involves retracting the plunger to around 0.2–0.3 mL, holding this position for a minimum of 5 to 8 seconds, and assessing for a flash of blood entering the syringe. The presence of this flash indicates that the needle has mistakenly been placed within a vessel, and the injector must withdraw and establish a different injection point. While specific, this safety checkpoint is not sensitive; the absence of a flash does not guarantee that the injection will be extravascular. Examples where a flash may not be observed include the use of highly viscous fillers and small needles, unintentionally pinning a vessel down to the supraperiosteal plane, or cases where the needle has inadvertently changed position. Due to the likelihood of false-negatives, the practice of aspiration is highly debated. Still, aspiration is advised in high-risk areas.

A recent study proposed a revised method for aspiration, where the needle is loaded with saline before being attached to the filler syringe. The authors hypothesized that aspirating with a saline-loaded needle would “open” a path of less resistance for blood to travel into the syringe. In vitro head-to-head testing of the traditional and saline-loaded aspiration techniques using 27- and 29-gauge needles with six different hyaluronic acid fillers found that traditional aspiration was positive only in a few trials with the 27-gauge needle and false in all 29-gauge needles. In contrast, aspiration with a saline-loaded needle resulted in positive aspiration with all needle sizes and fillers, along with exhibiting a significantly shorter time to flash. In addition to aspiration, some injectors may elect to use Doppler ultrasound or other imaging devices to help avoid intravascular injection. Still, no safeguard is totally reliable, nor do they replace an intimate knowledge of anatomy and injection technique.

Depending on filler viscosity, a degree of extrusion force must be applied to the plunger for the filler to plastically deform and begin to flow as a fluid. When injecting, it is important to use minimal force. Devastating vascular complications may involve retrograde flow of product through the arterial system, which requires a forceful injection that overcomes systolic blood pressure. It has been observed that typical injection pressures are fortunately lower than that required to cause propagation of filler intravascularly; however, the required force for intravascular propagation is only 50% to 75% the reserve strength of the fingertip and 5% to 10% that of the thenar eminence. Because the strength of the fingers could theoretically propagate a column of filler through an artery, injectors should never overcome met resistance by increasing injection force; rather, the injector should withdraw and reposition the instrument so that injection with minimal force can occur. Certain practices can help reduce extrusion forces. Analogous to the difference in fuel required to drive a car on an open road versus stop-and-go traffic, less force is required for continuous injection compared to injecting after every stop. Mixing fillers with lidocaine/epinephrine or normal saline reduces viscosity and thus lowers the required extrusion force. The addition of lidocaine/epinephrine can also obviate the need for additional anesthesia, and epinephrine may reduce the risk of bruising and vascular compromise.

The quantity of filler injected and rate of injection are additional variables related to successful injection. Even if a vessel is perforated, a slow injection will deliver a forward force less than the back pressure in the lacerated vessel, thus preventing introduction of filler into the lumen. Moreover, a slow injection rate allows tissue to equilibrate, which results in less pain. Limiting both the number of syringes per treatment and the amount of filler delivered per needlestick decreases the risk of intravascular and extravascular occlusion, along with the risk of biofilm formation. Generally, no more than 0.2 mL should be injected per individual thread or bolus. For example, if a 0.5 mL bolus of filler is desired to augment the lateral cheek, the injection should be divided into two smaller bolus injections. Too much filler, especially in areas like the tear trough, can lead to poor aesthetic outcomes such as the Tyndall effect and malar edema. It is better to undercorrect and follow up with a touch-up treatment several weeks after edema has resolved.

Because static rhytids form over underlying vasculature, such as the nasolabial crease over the angular artery and glabella lines over the supratrochlear and dorsal nasal artery anastomoses, rhytids can serve as a compass for needle placement. Needle placement parallel to rhytides increases the chance of residing within the arterial system compared to a perpendicular alignment. In contrast, parallel insertion with a blunt cannula is safer. A study examining different insertion angles of a 25-gauge cannula in relation to the superficial temporal artery found that perforation is most common when the cannula is aligned with a trajectory perpendicular to the neighboring artery. When injecting in high-risk areas such as the glabella or nasolabial folds, it is especially important to keep the injection instrument in constant movement. If blanching is observed or the patient reports pain, the injection must be immediately stopped and a prompt transition must be made to prevent or mitigate vascular compromise. Avoiding and managing vascular compromise are detailed in other chapters.