20 HOW TO TREAT : HYALURONIC ACID TISSUE FILLERS
20 HOW TO TREAT : HYALURONIC ACID TISSUE FILLERS
2 JUNE 2023 ausdoc . com . au
CD44 and RHAMM ). 23 , 24 Through these receptors , HMWHA dampens down inflammatory activity , aids in cellular motility and , through the dermis , influences cellular growth and longevity . Injected HMWHA is assumed to exhibit some of these characteristics , including the anti-inflammatory effect .
HMWA is eventually nibbled down and degraded into shorter and shorter fragments by the body ’ s hyaluronidases and any local inflammation elaborating substances , such as reactive oxygen species .
Once low molecular – weight hyaluronic acid ( LMWHA ) is produced by this process , these fragments can be digested by cells , such as macrophages . These fragments are much lower in weight , 20kDa , considerably lighter than native HMWHA . LMWHA molecules are capable of being endocytosed by immune cells and actively entice these into the area to perform this function . LMWHA is thus pro-inflammatory as these fragments excite immune cells to perform the function of mopping them up ; LMWHAs do this by interacting with pro- inflammatory receptors — toll-like receptors 2 and 4 . 25
It has been postulated that this degradation pathway may partly explain one of the complications seen with filler injections : delayed tissue nodules .
This How to Treat focuses on hyaluronic acid and its role in aiding tissue structure . It aims to ensure that GPs understand when to refer a patient , recognise when adverse effects are occurring and are able to keep patient expectations within realistic bounds .
3 Biotech 2016 ; 15 Feb / CC BY 4.0 : bit . ly / 3FSLLrN
HYALURONIC ACID TISSUE FILLERS
MANY will use the terms ‘ HA filler ’ and ‘ dermal filler ’ interchangeably ; however , this is largely inaccurate as only the most superficial of filler injections are intradermal . Almost all filler injections are intended for deeper injection , into the subcutaneous tissue and deeper , to aid in tissue function and volume . ‘ Tissue filler ’ appears to be a more accurate term .
HA is a viscoelastic substance — namely , it has elements of springiness , like an elastic band ( elastic , stretchy and resilient ), and spreadability ( viscosity ). It requires these properties to allow for its compression as it progresses down the narrow needle or cannula and then its release into tissues , where it is less constrained and can expand in the new environment . This viscoelasticity allows for a spectrum of behaviour to be built into the technologies underpinning the filler ’ s performance in tissues .
The science surrounding the behaviour of fillers in tissues is termed rheology . It describes the way manufacturers of HA fillers can manipulate the different elements , such as crosslinking , concentration and the use of variable-length chain lengths of HA elements to exploit these qualities . These variables allow fillers to provide rigid support almost like bone , on one hand , or to spread superficially , like honey , and to act like the skin ’ s superficial layers , as well as everything between these extremes . Those fillers designed to have a more solid structure in tissue tend to be deposited deeply , whereas others are designed to sit higher in tissue and move with the facial muscles of expression .
Figure 1 . Hyaluronic acid .
Hyaluronic acid biosynthetic pathway in Streptococcus zooepidemicus . Glucose is first converted by hexokinase to form glucose-6-phosphate , which then enters one of the two distinct pathways to form UDP-glucuronic acid ( pgm , hasC and hasB ) or UDP-N-acetylglucosamine ( hasE , glmS , glmM and hasD ). These precursors are then bound together via the action of hyaluronic acid synthase or HAS ( encoded by hasA in S . zooepidemicus ) to form hyaluronic acid .
Fillers are injected via sharp needles — usually provided with the product — or blunt-tipped cannulae , with the depth of injecting dependent on the filler ’ s designated purpose .
Neither technique is as accurate as the practitioner believes , with both instruments capable of causing most of the complications discussed later .
ANATOMY OF THE FACE RELEVANT TO FILLERS
THE face may be divided into two basic segments : the anterior face and the lateral face . The anteriorly placed tissues contain the muscles of expression ( see figure 3 ) and their supportive structures that allow for communication and speech and that support the important functions of vision and respiration . The muscles of expression are largely distributed around the two large areas of holes in the skeletal structure : the orbit and the periorbital tissues , and the perioral and perinasal complex .
The lateral face contains the muscles of mastication — chewing / grinding and clenching , see figure 4 . The muscles of mastication have additional societal roles in the designation of gender identity and dimorphism — masculine versus feminine — the attractiveness of the facial shape and the appearance of ageing .
These two areas of the face may be targets for HA fillers to shape or project the face optimally and supplement areas that may be ageing .
The two areas operate independently and are bolted to each other by a series of retaining ligaments that firmly attach areas of the face to bone or fascia of deeper layers . 26
There are five horizontal layers to the face : skin ( epidermis and dermis ); the subcutaneous tissue layer , which is also termed the superficial fat pads ; the muscular layer , with its investment of fascia ( also called the superficial muscular aponeurotic system ); the deep fat plane , which is divided into a series of deep fat pads ; and the bone , with its attached periosteum .
The facial fat compartments — both superficial and deep — are separated into compartments by a series of multiple variable intervening ligaments . 27 Vessels and nerves find their way between layers usually in the intervening ligaments of these compartments .
These fat compartments are important to fillers and relate to their appearance , especially on movement and structure .
The depth of filler determines its appearance , particularly on movement . Filler injected deeply into the deep structures ( the deep fat pads or at the level of the periosteum ) will behave as if it is bone , enhancing that layer and adding to the support of the face ; it will act as a supplement to the bone , projecting the more superficial layers . In the central part of the face , where the muscles of expression ( mimetic muscles ) lie , injection of filler deep into these muscles will not appear to move on expression as it is below these mimetic muscles . These muscles , which produce everyday expressions , will continue to contract independently above the layer of filler deposition .
However , if the filler is implanted superficially in the central part of the face , it will move with the muscles of expression . This is sometimes intended to give substance to the subcutaneous tissue to disguise wrinkling produced on the skin surface by the mimetic muscles . This wrinkling becomes more obvious as one ages and the subcutaneous tissue in some areas attenuates , allowing the muscle attachments to the skin to be more easily seen as wrinkles deepen with ageing .
Certain characteristics are necessary for fillers to operate well in the chosen depth of injection .
Deeper injections require a filler that permits a degree of shape retention ( elasticity ) to allow it to vertically force the projection of the layers of tissue superficial to the injection .
Filler injected into more superficial layers needs to be horizontally spreadable ( viscous ), allowing it to supplement the superficial tissues and coat the underlying muscles so they move smoothly without bunching up or producing an artificial appearance on movement . PAGE 22