CPD: Exploring Bone Ageing

Exploring Bone Ageing

Mr James Olding details how facial bones change over time and provides considerations for dermal filler treatment

Contemporary concepts in facial aesthetics have shifted the focus only two thirds of the amount that women lose over their lifetimes, to rejuvenation through revolumisation and identifying age-related in addition to reaching peak bone mass later (around aged 30) and volume loss, with the objective of re-establishing the ideal or having a higher adult peak bone mass. 4 In women, in addition to previous facial dimensions. The facial skeleton provides the structural gradual progressive loss of cortical and trabecular bone from the third support for overlying soft tissues, and changes to facial appearance decade onwards, additional bone loss occurs precipitously within a manifesting as hollowing, folds, creases and rhytids, are usually year of the menopause; a process which is sex hormone linked and preceded by bony changes. attenuated by hormone replacement therapy. 9 The idea of selective It is therefore of great importance that any structural deficit is bone resorption alludes to the site-specific changes in certain areas addressed. Facial ageing follows a predictable process, with specific of the face, while resorption elsewhere is less pronounced or not areas of the facial skeleton undergoing resorption, resulting in the present at all. 1 appearance of some of the most common stigmata of ageing. The Despite being regulated by different growth factors, facial bone mid-face, the orbit and the mandible are three important areas of the undergoes a decrease in bone mineral density with age, similar to facial skeleton implicated in ageing, and the signs of bony changes axial bone. 2 In the adult facial skeleton, it has been observed that in these regions include under-eye hollowing, altered brow position, bone resorption occurs in a predictable manner, commonly affecting deepening facial folds, and the appearance of jowls. 1,2 the mid-face, orbit and mandible, though each area is not necessarily The biology of bone remodelling Differences in bone density are well reported between ethnicities Bone is a living tissue maintained through a delicate balance of and black individuals have been shown to experience less osteoid deposition by osteoblasts, and resorption by osteoclasts. pronounced dimensional changes to the face than white individuals Understanding bone biology and its clinical relevance requires an as they age. 10 It is not possible to fully assess the reasons underlying understanding of some important terms; namely, peak bone mass these observed differences between ethnicities, though genetics is (PBM) and bone mineral density (BMD). Bone mass will depend on likely to be central, in conjunction with other factors including body bone density and bone size. 3,4 Each individual has a bone mass mass, hormones and diet. 11 potential which is largely determined by genetics. 3 Within this genetic potential, the actual peak bone mass reached as an adult will depend The mid-face on lifestyle, hormonal and environmental factors. 5 Research has shown that even within a single area of the face, Differences between sexes are also notable, with the peak bone bone resorption is highly site specific. 1,2,12 The bony mid-face mass achieved by males being greater due to increased periosteum consists principally in the maxillary and the zygomatic bones, with a deposition on account of the fact of males having larger and longer predilection for age-related resorption at the maxilla, even in dentate bones in general. 6 Sex hormones and the IGF-1 system have been patients. 1,2 Maxillary bone resorption leads to reduced anterior implicated in this sexual dimorphism. 7 Bone mineral density is a measure of the inorganic mineral content of bone, and is a surrogate for measuring bone mass and strength. It can be measured as a snapshot using a DEXA scan Inferiorlateral to diagnose conditions such as osteoporosis. orbital It is important to understand that the peak Glabella angle adult bone mass achieved will influence the risk of sequelae arising from bone loss, Maxilla Pyriform angle including osteoporotic fractures, in adulthood. 6 Maxilliary angle Bone responds to mechanical stress, undergoing remodelling, which involves resorption followed by deposition, in what is Prejowl suculus of mandible known as a basic multicellular unit of bone remodelling (BMU). 5 The adult skeleton is entirely replaced in this way every 10 years. 8 Starting from the middle of the third decade, affected by the same pathophysiological process. 2,10 women lose 35% of their cortical bone and Figure 1: Areas of the facial skeleton prone to age-related bone resorption Figure 2: Age-related resorption has been analysed in longitudinal studies using CT, where the glabella, 50% of their trabecular bone. 4 Men lose pyriform, and maxillary angles are measured over time

projection, resulting in an undermining of the structural soft tissue support in this region. Geometrical analysis using CT in longitudinal studies have shown that the maxillary angle decreases with age secondary to localised resorption. 2,13 The pyriform and glabella angles also decrease, with localised bone loss in these areas contributing to the classical features of mid-facial ageing. 2,14 Overlying fat compartments in both the superficial and deep layers are affected by mid-face bone loss. 14,15,16 An example of a common process involves a loss of zygomaticomaxillary bone, which undermines the medial and lateral sub-orbicularis oculi fat (SOOF), resulting in infraorbital hollowing and loss of lower lid support. 13 A worsening of the palpebromalar sulcus may also be observed. It should be emphasised that maxillary and zygomatic bone resorption has wide-reaching effects, leading to soft tissue descent and lower face ageing, as well as geometrical alterations of the entire face in both vertical and horizontal dimensions. 13,14,17

The orbit The orbit has been shown to undergo greatest resorption in two key areas. 18 Firstly, selective reabsorption at the inferolateral quadrant of lid-cheek junction, as well as herniation of the infraorbital fat. These periorbital issues are common reasons for patients seeking aesthetic treatment. Secondly, resorption at the superomedial aspect of the orbit results in a comparative lift of the medial brow, with an associated lower position of the lateral brow. This resorption usually occurs later in life, around the fifth and sixth decades. 17,19 Importantly, we must recognise the effect of bone resorption as the primary event here, followed by the appearance of soft tissue changes involving the fat, muscle and skin. 19 Progressive enlargement of the orbit occurs with age, however there are important differences between ethnicities. One recent longitudinal study showed that while increased orbital dimensions occur in all black and Caucasian populations, these increases are notably reduced in black females, and do not occur to any significant degree at all in black males. 20 Between the sexes, a study using CT imaging found that orbital aperture area and width increased in males and females, with a significant increase between the young (mean age 30 years) and middle-aged (mean age 54 years) female groups. 19 This change occurred later and over a more protracted time period in males, with significant increase found between the young (mean age 33 years) and old (mean age 75 years) age groups.

The mandible Previously, the mandible was believed to increase in size with age, 2,12,21,22 however, recent longitudinal studies looking at linear measurements have shown that the process is more complex, with concurrent expansion and resorption occurring. 23,24 In both males and females, linear measurements of the bigonial width appear to remain relatively constant with age, while mandibular length and height decrease. 25 The effect of reduced mandibular anteroposterior and vertical dimensions, coupled with overlying soft tissue changes, will contribute to the progression of jowls, and an exacerbation of the pre-jowl sulcus. 25 With areas of isolated concavity such as the pre-jowl sulcus, linear measurements do not permit longitudinal analysis of changes. 25 Age-related bone resorption in an anteroposterior dimension, similar to congenital microgenia, may result in mentalis hyperactivity, submental changes, and reduced definition at the mandibular lower border. 26 A strategy to address jowls must include a geometrical analysis of the patient’s profile, as well as close attention to any mid-face volume deficit. The lower face requires particular attention, in that it can be adversely affected indirectly by mid-face bone changes, as well as directly by lower face bone and dental loss. The squaring out of the face that occurs with age, in conjunction with muscle and skin changes, can have a profound impact on how patients feel about their apperance. 25,27 There is clear evidence concerning the impact of tooth loss on alveolar bone resorption of the mandible. 27 Alveolar bone and the tooth support each other, and upon tooth loss, resorption can be profound, especially in the mandible, which has the fastest rate of bone turnover in the body. 3 In addition to the morphological changes directly resulting from dental issues, the indirect effects of tooth loss must also be considered, where loss of the mandibular bone itself occurs, in conjunction with reduced masticatory functional forces affecting the muscles of mastication, including the masseter. 26 Tooth

the orbit may occur in middle age, leading to a lengthening of the loss can result in reduced vertical occlusal dimension and a reduced lower facial third length, as well as leading to the appearance of perioral concavity and perioral lines. 28

Injectable product selection In view of bone loss being the key step in facial ageing, it follows that treatments must aim to revolumise in areas of deficiency. The product used must possess ideal properties to enable preperiosteal placement and to optimise revolumisation after bone loss. Rheological properties, cross-linking, elasticity and cohesivity are important to analyse. 29,30 In regard to hyaluronic acid (HA) based products, a higher HA concentration will result in more water uptake and a more volumising effect. 31 Cross-linked HA is commonplace, and this affects both the longevity and the cohesivity. 32 Cohesivity can be defined as resistance to vertical compression, 33 and refers to the ability of a product to be moulded or sculpted to create lift and shape. 33,34 Higher cohesivity products are better at creating contours and shapes. 33,35 Cohesivity depends on the degree of attraction between cross-linked HA units, through weak, noncovalent forces, and it is a function of both the concentration and cross-linking of the HA. Elasticity refers to the ability to resist shear deformation, and a product with greater elasticity will be better able to maintain its original form after pressure or strain, giving it greater lifting capacity. 33 Examples of technologies commonly used in contemporary aesthetics include Vycross and Cohesive Polydensified Matrix (CPM) gels, with others available. 34 Vycross technology mixes high amounts of low molecular weight HA chains (promotes crosslinking with reduced need for the crosslinking agent BDDE) with smaller amounts of high molecular weight fibres (promotes cohesivity). 34 CPM technology involves a processing step whereby additional HA chains are added after stretching the matrix in the first part of the process. These added chains aid in the crosslinking process, reducing the amount of BDDE that is required. 34 Based on our understanding of products and properties, an example of a product that is suitable for use in the mid-face would be Juvéderm Voluma, from the Juvéderm Vycross range, with a HA concentration of 20mg/ml, and relatively high cohesivity and elasticity. An alternative HA product would be Belotero Volume, using CPM technology, which has a similar longevity to Juvéderm Voluma, of around 18 months. Note that there are many other products available that are also suitable. Mid-face treatment strategies should account for any bone loss in the

Before

After

Figure 3: Mid and lower face revolumisation in a 52-year-old female patient. Zygomaticomaxillary and alveolar bone loss predominated here. Revolumisation was carried out with Juvedérm Voluma to the mid-face, Juvedérm Volbella to the infraorbital region and Juvéderm Volux to the lower face. Onabotulinumtoxin A to the upper face carried out at same time as dermal filler treatments – the positive effect on brow form and position can be seen.

anteromedial cheek, the zygomatic eminence, and on the zygomatic arch, and injections are delivered as boluses onto the periosteum. 34,36 It is my view that anchoring at the zygomatic arch is the most important step in any mid-face strategy, though exact volumes and areas injected will depend on individual patient assessment and treatment planning. Where new volume or contours are sought, such as in the lower face, in addition to possessing the above properties, the product must have a high level of cohesivity. 33 Juvedérm Volux is one example of a suitable product for this purpose, containing 25mg/ml of HA, and the highest cohesivity, elasticity and water-retaining ability of the Juvéderm Vycross range. 37 Restylane Volyme is an alternative product for use, with 20mg/ml HA, but others are also available. A strategy to volumise the lower face may involve pre-periosteal bolus injections onto the mandibular angle and at the pre-jowl sulcus. High cohesivity is key to enable the product to resist deformation and to provide the necessary support to overlying soft tissue in the lower face. 38 In the periorbital region, greater care must be taken when injecting dermal filler due to the rich periocular arterial anastomoses, which provide a route for an HA embolus to reach the ophthalmic artery and affect the vision. This is in addition to greater risk of bruising due to rich venous plexuses, and special challenges in correctly diagnosing and treating periorbital issues due to the complex anatomy involving superficial and deep fat, as well as issues affecting the muscle, skin and bone. 35 Pre-periosteal placement on the inferior orbital rim must be carried out using a product with low HA concentration to confer low waterretentive ability, and low elasticity to promote better flow properties and more homogenous tissue integration. 39 Under correction is also important to prevent hydrophilic HA fillers causing unwanted swelling which can affect aesthetics and lymphatics. 40 Injecting in this area may form part of a strategy to address a tear trough deformity, however it is important to assess the maxilla and zygoma, and to treat these areas before moving to the infraorbital region itself, in that zygomaticomaxillary bone loss precipitates and propagates loss of lower lid support, anterior cheek flattening and descent of the SOOF. 12 As such, bone loss must be treated directly (at the orbit) and indirectly (at the mid-face). Conclusion Bone loss is a key factor in facial ageing, occurring in specific areas and in a predictable pattern. The orbit, maxilla and mandible all undergo age-related resorption, and lifestyle factors, ethnicity and dentition play important roles. Understanding the relationship between the different layers and tissues of the face is fundamental to addressing our patients’ concerns, and bone changes must be considered at the outset of any facial assessment. Knowledge of when, how and which individuals are affected will enable you to pre-empt and treat this crucial initiating step in the process of facial ageing.

Mr James Olding is an aesthetic doctor and injectables trainer. He is also training in oral and maxillofacial surgery in the NHS. Mr Olding studied medicine at the University of Bristol, is a member of the Royal College of Surgeons, and is in his final year of studying dentistry (DPMG course) at King’s College London. Qual: MBChB (Hons), BSc (Hons), MRCS (England)

TO VIEW THE REFERENCES GO ONLINE AT WWW.AESTHETICSJOURNAL.COM

Test your knowledge! Question Possible answer

Selective bone resorption affects which part of the orbit first? A. Superolateral B. Superomedial C. Inferomedial D. Inferolateral

Peak bone mass attained by an individual is not dependent on which of the following? A. Eye colour B. Genetics C. Diet D. Hormonal factors

Mandibular tooth loss has no effect on which of the following? A. Reduced vertical occlusal dimension B. Maxillary alveolar bone C. Masticatory function D. Mandibular alveolar bone

In respect to hyaluronic acid-based products, which of the following is false regarding cohesivity?

Through bone remodelling, the adult skeleton is replaced in its entirety how frequently? A. It is related to the degree of HA cross-linking B. It refers to the ability to resist shear deformation C. It refers to the ability to resist vertical compression forces D. It is related to the HA concentration

A. Every 2 years B. Every 5 years C. Every 10 years D. Every 20 years

Answers: D, A, B, B, C