Keywords
pinch anatomy - fillers - dermal filler - filler injection - facial anatomy - injection anatomy - hyaluronic acid - filler complications - filler technique - forehead fillers
Soft tissue augmentation with fillers is a minimally invasive procedure that provides a quick and satisfying esthetic outcome with reasonably good predictability. Minimally invasive esthetic procedures, especially filler injections, have seen increasing popularity in the last decade. As per the statistics given by the American Society for Aesthetic Plastic Surgery (ASAPS) for the top five nonsurgical esthetic procedures performed in 2016, hyaluronic acid dermal fillers ranked second to botulinum toxin injections with 2.49 million procedures in the United States alone.[1] This exponential demand has necessitated that more injectors do this procedure and learn the injection skills.
During training for fillers, much emphasis is given on teaching the facial anatomy concerning injections, that is, the injection anatomy.[2] However, changes in the tissue layers’ anatomy due to their manipulation during filler injection have not been discussed in detail. The anatomical change of these tissue layers during pinching or pulling has been studied as “pinch anatomy.”[3]
[4]
The Concept of “Pinch Anatomy”
Various facial structures are shown in their natural, rested appearance in the images of cadaver dissections or medical illustrations. They are shown without any distortion caused by pinching or pinching with pulling. Commonly, clinicians perform filler injections with their dominant hand while pinching and pulling the skin fold with their nondominant hand. During pinching, the anatomy of tissue layers, known as “pinch anatomy,” becomes different from their natural appearance externally and internally.[5] While the external changes caused by pinching on the skin are visible on the skin surface, the injectors should be aware of the changes caused by these deformational forces in the deeper tissue layers. In understanding the concept of “pinch anatomy,” it is essential to know the terms like “pinch,” “pinch and pull,” and “gliding plane.”
A “pinch” can be described as a maneuver using the thumb and adjoining fingers to hold the tissue layers as a fold. As per the Oxford Dictionary, the word “Pinch” means “to grip (something, typically a person's flesh) tightly and sharply between finger and thumb.”
While pinching bunches up the skin in a fold, the potential space under the pinch is still limited. However, simultaneous “pinch and pull”[6] movement or a deep pinch can change this limited space into a much larger space between the layers at the level of the glide plane. The “pinch and pull” maneuver has also been described earlier as pinching or tenting[7] method for filler injection.
The term “glide plane” can be described as a plane between the tissue layers, allowing easy movement of superficial tissue layers over the deeper layers.[8] This plane is also important during the “pinch and pull” maneuver as the mobile superficial layers get pulled up over relatively fixed deeper layers. This plane is a potential space that gets increased during the pulling up of superficial tissue layers.
“Pinch Anatomy” of the Forehead Tissue Layers
The forehead consists of a thick layer of skin that overlies a subcutaneous fat layer to which it is firmly attached. Just deep to the subcutaneous fat layer is the galea aponeurosis. This layer of the forehead envelopes a pair of frontalis muscles. Deep to the galeal layer is the loose areolar tissue lying between the galeal layer and the pericranium. The musculoaponeurotic layer is attached to the skin by retinacular cutis fibers passing within the subcutaneous fat layer. The outer three layers are fused in a functional unit, separated from the periosteum, and bone by the loose areolar tissue layer.[9] With the frontalis muscle contraction, the three superficial layers of the forehead glide for short distances over the underlying periosteum with loose areolar tissue providing the glide plane.[10]
[11] This glide plane of galea moving over the periosteum influences the aging process and allows surgeons to rejuvenate the upper face by elevating the sagging soft tissues. The scalp flap can be easily dissected during plastic surgery procedures because the loose areolar tissue allows easy gliding movement of the composite scalp over the fixed layers underneath, that is, periosteum and bone.[12]
When the gentle pinch is applied to the tissue layers in the forehead, the skin and subcutaneous fat layer constitute the tissue layers in a pinch ([Fig. 1]). The frontal branch of superficial temporal artery (STA) and its transverse branch run on the superficial surface of the galea aponeurotica layer[13] ([Fig. 2]), and the layers in the gentle pinch are just superficial to these important vessels. This change is quite similar to the changes induced by gentle pinching in the temple. The supraorbital and supratrochlear vessels are found on the galeal surface of the upper two-thirds of the forehead after becoming superficial from their deep location in the lower one-third of the forehead. The deep pinch or “pinch and pull” maneuver in the upper two-thirds of the forehead pulls up the skin, subcutaneous fat, and galea layers along with the frontal branch of STA, supratrochlear (ST) artery, and supraorbital (SO) artery, with all of them running on the surface of the galea ([Fig. 3]). Loose areolar tissue provides a subgaleal glide plane to the mobile superficial tissue layers of the forehead for movement over the fixed tissue layer, that is, periosteum[14] ([Table 1]). By deep pinching/pinching and pulling, the potential space in the relatively avascular, loose areolar tissue layer in the forehead is increased ([Fig. 4]). This space can then be utilized for filler injection with needle/cannula in the forehead with minimum risk of vascular complications ([Figs. 5] and [6]; [Video 1] [available in the online version]).
Fig. 1 The picture shows the “gentle pinch” maneuver with the thumb and index finger in the forehead.
Fig. 2 The cadaver dissection showing the course of the frontal branch of STA on the surface of STF in the temple and galea in the forehead. It also indicates branches of SO and ST in the superficial plane in the upper two-thirds of the forehead (cadaver dissection image contributed by author K.M.K.). SO, supraorbital; ST, supratrochlear; STA, superficial temporal artery; STF, superficial temporal fascia; M, muscle; Br, branch.
Fig. 3 The picture showing the “deep pinch” or “pinch and pull” maneuver in the forehead, with thumb and index finger.
Fig. 4 The cadaver dissection showing “pinch anatomy” of the forehead with the superficial mobile layers gliding over the periosteum to bunch up, creating more space for the bevel of a needle during filler injection in the loose areolar tissue layer (cadaver dissection image contributed by author K.M.K.).
Fig. 5 The cadaver dissection showing “pinch anatomy” of forehead during a deep pinch, creating more space so that complete bevel of the needle is present in the relatively avascular, loose areolar tissue layer during filler injection (cadaver dissection image contributed by author K.M.K.).
Fig. 6 The cadaver dissection showing the location of filler material (green color) in the relatively avascular, loose areolar tissue layer on the periosteal layer of the forehead when a deep pinch is used to create more space in this layer (cadaver dissection image contributed by author K.M.K.).
Table 1
Table showing the summary of changes in pinch anatomy with “gentle pinch” and “deep pinch” in the forehead region
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Gentle pinch
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Deep pinch/pinch and pull
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Tissue layers involved
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It bunches up skin and subcutaneous fat with minimal movement of galeal layer
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It separates skin, subcutaneous fat, galea layers from the periosteum
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Vascular relation
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Frontal branch of STA, branches of SO/ST arteries run in a plane in the superficial part of Galea just deeper to the pinched tissue making it a no-go danger zone in the upper two-thirds of forehead
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Relatively avascular loose areolar tissue plane lies deeper to the pinched tissue creating more space in it for cannula or the needle bevel, the vessels being pulled up in the pinched tissue
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Injection advice
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This plane is ideal for superficial placement of skin rejuvenating fillers. The plane deeper to this pinch is a “No-Go zone” for filler injections in the upper two-thirds of the forehead
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The plane deeper to this pinch is ideal, safest plane for filler injection in upper two-thirds of forehead
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Abbreviations: SO, supraorbital; ST, supratrochlear; STA, superficial temporal artery.
Video 1 Showing injection of filler material (green color) in the relatively avascular, loose areolar tissue layer on the periosteal layer of the forehead when a deep pinch is used to create more space in this layer (cadaver dissection video contributed by author K.M.K.).
Discussion
Filler injections are minimally invasive in comparison to surgical procedures. The key advantages of the filler procedure are shorter procedure time, quick recovery, and theoretically lower possibility of complications. However, while performing the filler injections, one should be cautious not to inject in the blood vessels as significant complications, like skin necrosis[15]
[16] and vision loss,[17]
[18]
[19] have been reported with accidental intra-arterial injection. In addition, nonthrombotic pulmonary embolism has also been reported with accidental intravenous injection of fillers.[20]
Therefore to maximize the value of filler treatment, the aim should be to minimize the possibility of vascular complications by placing the fillers in the correct plane and away from arteries.[21] It is difficult to learn for injectors as consistently reaching the right injection plane with a needle or cannula is not easy. It requires training for injectors by imparting them the knowledge of arterial and tissue layer anatomy. The knowledge of the precise location and correct depth of major blood vessels, based on facial surface anatomy, is necessary for safe and effective filler injections. During cadaver training or as depicted in anatomy manuals, vital anatomical structures are shown in their natural, undistorted positions.[22] However, pinching and pulling with the nondominant hand during filler injection distorts the tissue anatomy.[5] The impact of pinching on the anatomy of the tissue is now being studied as “pinch anatomy.”[3]
[4]
During filler injections, there are two crucial factors to be considered. One is to avoid important arteries, and the other is the filler placement in the right plane.[23] With the knowledge of pinch anatomy, using different pinch methods and the relationship of the critical structures with the tissue layers pulled up in a pinch, clinicians can target specific planes for filler injection while avoiding the important vessels.
During the pinch procedure, consideration for the depth and course of major arteries in that region is essential. During the pinch procedure, it is crucial to learn which layers of the face get separated from deeper layers. During the “pinch and pull” procedure in an area, it is vital to know whether the blood vessels are pulled upward with the tissue layers or not. If the blood vessels are thought to be pulled up with a “pinch and pull” maneuver, injecting the filler in the deeper layer would be much safer. If the blood vessels are not pulled up with “pinch and pull,” injecting the filler in the superficial layers in a pinch would be safer.[3]
In a study on temporal fossa, the depth of the skin pinch was tested with a gentle pinch and a deep pinch. Skin from the pinched area was cut in both situations to determine if there was any difference in the movement of tissue layers, based on the strength of the pinch applied. It was found that when the cutting was done on the gentle pinch, only skin and the subcutaneous fat layer were cut with no damage to the superficial temporal fascia (STF) and STA. However, when the pinch was performed deeply with more pressure, the STF was found cut in addition to skin and subcutaneous fat, and the deep temporal fascia (DTF) was exposed. The exposed DTF was not damaged at all.[3]
Filler injection in the forehead is technically challenging. As filler injection in this area is a blind procedure, it is difficult to assess whether the needle or cannula is in the subcutaneous plane or has reached up to the periosteum. When a pinch of tissue layers is made, the superficial mobile tissue layers separate from the fixed deeper tissue layers before being pulled up. The risk of intra-arterial injection can be reduced by pinching/tenting the skin to provide more space in the avascular glide plane layer.[24]
The tissue layers behave similarly in the forehead, another anatomical area in the upper face for filler injections besides the temporal fossa. Based on the pinch anatomy, some conclusions can be drawn about the behavior of tissues in the forehead. With a gentle pinch in the forehead, only skin and subcutaneous fat layers are present in a pinch. However, when a deep pinch is applied on the forehead and tissue layers are pulled up (“pinch and pull”), the galea aponeurotica layer with the frontal muscle bellies gets separated from the periosteum. This separation happens at the level of the loose areolar tissue layer between the galea and periosteum. Like the temple, the loose areolar tissue layer acts as a glide plane in the forehead also.[25]
[26] Movement of the eyebrow is also facilitated by loose areolar tissue and galea fat pads under the frontalis muscle which forms a glide plane for reversible relative movement of superficial layers over deeper tissue.[27]
The “pinch and pull” maneuver lifts the superficial mobile tissue layers away from the fixed layer in depth, that is, the periosteum covering the bone. As the blood vessels in the upper two-thirds of the forehead are pulled up with a “pinch and pull” maneuver, injecting the filler in the deeper layer would be much safer. As the blood vessels, that is, SO artery and ST artery, in the lower one-third of forehead and brow region, are not pulled up with “pinch and pull” maneuver, injecting the filler in the deeper layer in the lower third would be dangerous, and superficial filler injection plane is preferred, especially in the brow region.
Fillers in the forehead are indicated for overtly concave appearance.[28] The popular method to inject the forehead is with a needle or cannula in the supraperiosteal plane.[29] In the forehead, the plane between the galea and periosteum provides a relatively avascular plane.[30] Injecting fillers in this plane can be a daunting task due to thin tissue layers in the forehead.[31]
[32] The concept of “pinch anatomy” can help in enhancing injection skills in the forehead region also. The important vessels in the forehead should be considered before filler injection. The frontal branch of the superficial temporal artery lies superficially on the surface of the galea.[33] The loose areolar tissue plane between the galea and periosteum has no major artery and is best suited for the forehead filler injection.[34] The “pinch and pull” maneuver in the forehead lifts the mobile tissue layers, that is, skin, subcutaneous fat, and galea, creating an injection space in the loose areolar tissue plane in the forehead. This simple maneuver with the nondominant hand creates a space in the loose areolar tissue layer of the forehead for safe filler injection. Another advantage of the injection with the “pinch and pull” technique is that the surface irregularities are less visible, and filler spreads easily in this plane after injection. Pinching or tenting the skin provides more space deeper to superficial branches of main arteries by pulling them away from the underlying safe plane.[35]
During the “pinch and pull” maneuver, the potential space in the loose areolar tissue plane increases. The bevel of the needle is more likely to be entirely in the loose areolar tissue due to an increase in space created by the “pinch and pull” maneuver ([Figs. 5] and [6]). The complication caused by the presence of bevel in multiple tissue layers[29] can be mitigated to a large extent by the “pinch and pull,” potentially providing more free space for the entire bevel of the needle to fit.
Conclusion
Using the nondominant hand to make a pinch or a “pinch and pull” maneuver can help reach the correct tissue plane. Knowing this change in the anatomy of tissue layers during the pinched state can help filler injection in the correct tissue plane of the forehead. Thus, “pinch anatomy” can act as an injection guide for filler injection and possibly help avoid an inadvertent injection in the blood vessels. Hence the knowledge of the pinch anatomy can potentially make a filler procedure safer, more precise, and effective in the temple and forehead regions.
