In order better to understand how a breast implant will interact with the overlying soft tissue cover, it is helpful to have a basic understanding of how an implant is made. Very simply, there are two basic components which become important in breast implant construction: the shape of the outer shell and the nature of the material used to fill the implant to give it volume.

The outer shell is made of a silicone rubber that is cured onto a form called a mandril. The mandril is specifically constructed to create an implant of a specific size and shape. For a given implant design, there are generally whole families of mandrils which maintain the basic shape but exhibit a wide range of graduated dimensions and volumes. Either the mandrils are dipped into liquid silicone or the silicone is sprayed on to apply a thin coat of the material to the mandril. This thin layer of liquid silicone is allowed to dry and the mandril is then dipped again. After a series of dips, the silicone layer that is now attached to the mandril has a uniform thickness sufficient to hold reliably a given volume, the configuration of which is determined by the shape and dimensions of the mandril that made the shell. The flexible silicone shell is cut free from the dipping rod attached to the mandril and the elastic form is stretched and pulled off. For saline implants, the circular defect created by freeing the shell from the mandril is patched and a small fill valve is inset into the patch to complete the construction of the shell. For silicone gel implants, the shell is filled with a prescribed volume of the chosen gel and the defect is then patched to seal the gel inside the shell (Figure 3.3 A–E).

Figure 3.3 (A) Appearance of an anatomically shaped mandril attached to a dipping rod just after it has been submerged into a vat of liquid silicone. The excess silicone can be seen running off the most dependent portion of the mandril. Once the excess silicone has been removed, a thin silicone layer is left to dry around the mandril. After several ‘dips’, a shell of uniform thickness is created around the mandril. (B) After the silicone rubber in the shell has cured, the shell is cut free from the dipping rod and pulled off the mandril. The elastic nature of the rubber allows this to be performed without damaging the shell. (C) Appearance of the fully formed shell after it has been removed from the anatomically shaped mandril. (D) A patching process is utilized to repair the circular defect created in the back of the shell by cutting the shell free from the mandril. (E) Appearance of the final breast implant after filling the anatomically shaped shell with a cohesive silicone gel. Courtesy of mentor Corporation ©

Although there are many variables involved in the design of a breast implant, the two that most directly influence how the implant will perform in a patient are the inherent shape of the outer shell as determined by the mandril and the volume and consistency of the filling material that is added to the elastic shell. How these two variables interact with each other directly affects how well the implant will function. In simple terms, the eventual shape of the implant is governed by the laws of physics as they apply to the act of adding volume to a confined space. This can be best understood by considering how an implant shape changes as it goes from being completely empty to being slightly overfilled.

When an implant shell is completely empty, the outer shell is wrinkled and the shape of the device is correspondingly distorted. As volume is added to the implant, the wrinkles are filled out and the shape progressively improves until, eventually, a volume is reached where the shell is completely filled and, without any other outside influences, the shape of the implant exactly approximates the shape of the mandril that made the device. However, because the outer silicone rubber shell is elastic, it is possible to continue to fill the implant to a point beyond the fill volume determined by the mandril. As a result, the surface area of the implant expands slightly and the intraluminal pressure of the device increases (Figure 3.4). It is at this point that the physics-based relationships between surface area and volume become important. Very simply, for a given volume, the smallest surface area that can contain that volume assumes the shape of a sphere. Put another way, a sphere describes a surface area to volume relationship that is maximally efficient. This explains why breast implants appear rounded when they are subjected to the forces of capsular contracture. Because the volume of the device is fixed, as the surface area of the capsule decreases due to the contracture, the relationship between the surface area of the capsule and the volume of the implant becomes more efficient and gradually assumes the shape of a sphere (Figure 3.5 A,B). Therefore, with a perfectly spherical implant shell, overfilling would result in an increased intraluminal pressure and a symmetrically realized increase in the surface area of the implant with no distortion in the shape of the device (Figure 3.6). Essentially, all that would result would be a slightly bigger sphere that felt a little firmer. However, breast implants are not spherical in shape and it is very important to realize that what are commonly referred to as round implants are round only in two dimensions. Typically, in the horizontal and vertical planes, the devices are symmetric. However, in the sagittal plane, the dimensions of the implant are different and, in that regard, what is typically referred to as a round implant is actually shaped (Figure 3.7). Although this typical ‘round’ implant does not approach the degree of shape that the more standard ‘anatomical’ implant does, it is shaped nonetheless as it has asymmetrical dimensions in one plane and therefore functions as an asymmetric device. This asymmetry in shell design has implications in how the implant responds to filling. As the implant proceeds from an empty state to one of progressive inflation, the shape will improve until that point is reached where the exact volume that corresponds to that of the mandril is reached. This is the optimal fill volume for the implant. As this optimal fill volume is exceeded and the implant becomes overfilled, the surface area of the device increases slightly and the pressure inside the device increases. As continued filling proceeds, the ability of the outer shell to stretch to accommodate the increasing volume becomes overwhelmed and the increase in the surface area of the implant tails off rapidly such that the surface area measurement becomes more or less fixed. At this point, the laws of surface area to volume physics become applied and the device gradually becomes more spherical and the projection in the sagittal plane increases and the vertical height and horizontal width diminish. Because the contour of the radius of the device is more aggressively shaped as compared to the smoother dome-like contour of the front and back of the implant, the ability of the elastomer in this part of the shell to stretch smoothly to re-accommodate the increasing volume of the implant is limited. Therefore, as the projection of the implant increases, the change in the shape of the device cannot be smoothly accommodated along the radius of the device and stress risers form at the implant edge. This is a well-recognized phenomenon noted particularly in saline implants and this edge distortion is known as ‘scalloping’ (Figures 3.8–3.10, (uDVD clip 1.05)). As the implant is overfilled even further and becomes more spherical, the edge scalloping becomes more severe. Recalling the example of capsular contracture, where the volume remains fixed and the surface area gradually decreases, here in the case of an overfilled implant, it is the surface area which becomes more or less fixed and the volume which increases. In either instance, it is the physics of adding of fluid to a confined space that ultimately governs the resulting shape of a breast implant.

Figure 3.4 Schematic diagram depicting the course of events that occurs as a breast implant is filled. Initially, the implant begins as an empty shell devoid of any shape. As fluid is added to the device, the shape gradually improves until the maximum volume of fluid is added to the device as dictated by the volume associated with the mandril that made the shell. It is at this point that the shape of the implant most directly corresponds to the shape dictated by the mandril. Because the outer silicone rubber shell is elastic it is possible to overfill the implant beyond the optimal fill volume. When this occurs, the surface area of the device expands slightly and the pressure inside the implant increases.

Figure 3.5 (A) Appearance of the operative specimen after bilateral complete capsulectomy in a patient with severe capsular contracture after breast augmentation. In each breast, the implant and the surrounding capsule were removed en masse. Note that each breast implant has been forced into a rounded shape as the fixed volume of the device was constrained by the contracted capsule. This phenomenon is predicted by the laws of physics as the fixed volume of the implant becomes encased in the smallest surface area possible as a result of the contracted capsule, the shape of which approaches that of a sphere. (B)After the capsule is removed, the implant is allowed to relax and the surface area of the shell effectively increases. As a result, the implant readily assumes the shape dictated by the mandril that made the shell.

Figure 3.6 Schematic diagram depicting the overfilling of a spherical-shaped shell. As fluid volume is added to a point beyond the maximal fill volume, a progressive increase in the surface area of the shell is evenly distributed over the entire surface area of the sphere, in association with an increase in the intraluminal pressure of the device.

Figure 3.7 Schematic diagram illustrating that what is commonly referred to as a ‘round’ breast implant is a misnomer as such a device is actually shaped due to the fact that it is asymmetrically constructed in the sagittal plane.

Figure 3.8 Schematic diagram demonstrating the effect of overfilling a ‘round’ breast implant. Because of the design asymmetry present along the radius of the device, stress risers develop along the peripheral edge of the implant as it is gradually overfilled. The subsequent deformation that develops along the radius of the shell of the implant is referred to as ‘edge scalloping’.

Figure 3.9 (A) Lateral view of a smooth round saline implant that is underfilled relative to the optimal fill volume. (B) As the implant is filled to the optimal fill volume, the projection increases and the overall shape of the shell is smooth with no irregularities. (C) As the implant becomes overfilled, the projection increases as the device becomes more spherical, resulting in the development of prominent edge scalloping along the radius of the device.

Figure 3.10 (A) The same underfilled smooth round saline implant viewed from the top. Note the central depression in the shell indicative of the fact that the implant is filled to a point that falls short of the optimal fill volume. (B) When the implant is filled to the optimal fill volume the central depression disappears. (C) When the implant is overfilled, prominent edge scalloping can be readily identified.

By applying these concepts, it is possible to gain a better understanding of implant behavior with regard to, in particular, saline implants. Figure 3.11 represents a stylized graph showing implant shape on the Y axis and degree of implant fill on the X axis. Initially, the implant is empty and the shape is an unfilled shell. Then, as fluid is added to the device, the wrinkles in the device are filled out and the shape gradually improves until the optimal fill volume, or the fill volume determined by the implant mandril, is reached. As further filling proceeds, scallops develop at the edge of the implant and the shape begins to deteriorate. Therefore, with the optimal fill volume as the apex of the desired shape, there is a small window of fill volume variability either side of which will still allow an acceptable shape to be created in the implant. Falling too far short of the optimal fill volume will result in progressively prominent wrinkling in the shell and exceeding the optimal fill volume by too great a degree will result in scalloping of the implant edge (Figure 3.11). This fill volume window has long been recognized by plastic surgeons and manufacturers and it is generally accepted that the optimal fill volume of a saline implant can be exceeded by roughly 10% without creating an obvious shape distortion. Such flexibility in implant filling is one of the advantages afforded by the use of saline implants. By differentially filling an implant of the same basic size and dimension without causing a significant distortion in the shape of the device, patients who present with mild asymmetries in breast size can be treated effectively without the potentially troubling need to resort to implants of different base diameters.

Figure 3.11 Schematic diagram illustrating how the shape of a saline implant changes in relation to the fill volume. As fluid is added to the device, the shape gradually improves until the optimal fill volume is reached. Filling the implant to a point just short of the optimal mark or, conversely, overfilling just beyond defines the fill volume range for the device that will still create an appropriate implant shape. Falling too far short of this mark will result in wrinkling in the implant shell and overfilling too aggressively will create edge scalloping.

These principles are equally applicable to ‘round’ silicone gel implants. However, when comparing the characteristics of saline versus silicone gel implants, it is important to recognize two major differences. First, the volume of a silicone gel implant is fixed, a feature that actually simplifies the use of these devices to a certain extent. Second, every silicone gel implant, whether it be a moderate-, moderate plus- or high-profile device, is underfilled relative to the optimal implant volume created by the mandril. This mismatch in fill volume relative to the available surface area of the device, along with the thicker consistency of the gel, results in an implant which has a decidedly softer feel than a properly filled saline implant. When a silicone gel implant is placed on a flat surface, the degree to which it is underfilled can be assessed by noting the variable degree of collapse of the central part of the shell in the middle of the device (Figure 3.12 A,B). This central shell collapse can be temporarily corrected by gently placing an evenly applied force to the surface of the implant. The implant then assumes a properly filled appearance without deformation. A similar phenomenon occurs when the implant is placed upright 90 degrees. The underfilled device will collapse in the upper pole, sometimes markedly, and this collapse can be partially overcome by applying force to the anterior surface of the device (Figure 3.13 A,B). In situ, this external force is applied to the implant by the surrounding soft tissue framework of the breast. Therefore, the outward appearance of a breast augmented with an underfilled fixed-volume silicone gel implant will depend upon the degree of underfilling of the device as modified by the nature of the external forces applied by the soft tissue framework of the breast.

Figure 3.12 (A) Lateral view of a moderate-profile smooth-walled silicone gel implant. A prominent area of central collapse is noted, indicating that the implant is underfilled relative to the optimal fill volume created for this particular shell by the mandril. (B) Lateral view of a high-profile smooth-walled silicone gel implant. The central collapse is less prominent, indicating that this device, although slightly underfilled, more closely approximates the volume of the mandril that made the shell. For this reason, high-profile devices are less likely to form prominent wrinkles in situ as they do not undergo the same degree of positional deformation that moderate-profile implants sometimes demonstrate.

Figure 3.13 (A) When a silicone gel implant is placed upright 90 degrees, the upper pole of the device collapses as, under the influence of gravity, the gel preferentially fills the lower pole of the implant. (B) When a counterbalancing force is applied to the lower pole, some of the gel is forced back up into the upper pole such that the degree of deformation in the upper pole becomes less. Clinically, this can be observed when the soft tissue framework of the breast is somewhat tight. The lower pole of the implant is not allowed to expand unchecked and the degree of upper pole collapse is reduced.

Given these variables, it can be deduced that saline-filled devices must be filled to a level at or near the optimal fill volume of the device lest the resulting surface irregularities which would develop, either wrinkles or scallops, become visible through the breast. These surface irregularities become even more pronounced when what appears to be a properly filled saline implant is placed upright 90 degrees. In this position, the pressure of the saline falling to the lower pole of the breast creates collapse of the upper pole with pronounced folding and wrinkling being the result (Figure 3.14). Applying force to the surface of the device, as happens with a relatively constricted soft tissue envelope, will counteract the tendency for the saline to fall to the bottom of the shell and upper pole distortion will tend to be corrected. However, in a lax skin envelope, if the soft tissue cover is thin enough, these irregularities develop unchecked and implant distortion with visible contour irregularities in the breast can potentially be seen. Silicone gel implants are under less severe constraints and can be underfilled without causing the same degree of potential surface irregularity. This is due to the fact that the denser consistency of the gel and the softer elasticity of a silicone gel implant shell combine to form softer wrinkles, which create edges which are less sharp than in saline devices. As a result, a fixed-volume, underfilled, silicone gel implant can settle to the bottom of a breast pocket and can fold and wrinkle according to the dictates of the overlying soft tissue framework to assume a shape other than that imparted to the shell by the shape of the mandril. Simply stated, the wrinkles associated with a standard round silicone gel implant tend to be much softer than those which form in saline devices and result in visible surface irregularities only in the thinnest of patients. In actuality, this shape is variably and at times markedly anatomical, a fact which has been documented in supine, prone and most importantly upright magnetic resonance imaging (MRI) evaluations of patients with fixed-volume silicone gel implants in place (Figure 3.15 A–G). When the soft tissue envelope is sufficiently lax, the underfilled gel device settles to the bottom of the pocket and forms folds and wrinkles in a patient-specific fashion to create, along with the overlying breast tissue, the final shape of the resulting augmented breast. This is actually a very powerful way to use a breast implant as each device is molded into a custom-made shape specific for each patient. When the volume and eventual configuration of the round gel implant complements the native breast well, very aesthetic results can be reliably and consistently obtained in breast augmentation.

Figure 3.14 Because saline is a much more free-flowing filler than silicone gel, the degree of upper pole collapse seen in an upright saline implant tends to be more pronounced than that seen in gel implants.

Figure 3.15 (A) View of a patient seated in an upright .6 Tesla MRI scanner. (B) A specialized breast coil is placed on the patient to allow upright imaging of the implant. (C, D) AP and lateral views of a patient after undergoing an augmentation mastopexy using a 325 cc smooth, round, moderate-profile silicone gel implant placed in the subglandular plane. (E) In the prone position, a prominent fold is noted in the anterior portion of the implant shell. (F) In the supine position, the breast and the underlying implant rotate superiorly, resulting in a smoothing out of the shell of the implant. (G) In the upright position, the takeoff point of the apex of the device forms an acute angle, which in a sense, creates an anatomic implant shape. Also, the folds return to the anterior surface of the implant. These findings demonstrate that the underfilled moderate-profile device is molded by the soft tissue framework of the breast into a patient-specific shape that, together with the existing breast volume, combines to create an aesthetic breast contour. This strategy of using an underfilled device that is shaped by the overlying breast is a very versatile and powerful method of optimizing the result in breast augmentation.

However, in assessing the shape of an in situ breast implant, the presence of wrinkles in the implant shell and what effect these wrinkles might have in both the short and the long term must be carefully considered. As long as these wrinkles form softly enough to allow the implant to settle into a smooth anatomic shape and cannot be seen through the soft tissue cover of the breast, they are well tolerated. However, over time, wrinkles eventually create weak points in the implant shell and may well be the major etiologic cause of ultimate implant failure (Figure 3.16 A,B). It is here that the anatomically shaped implant concept offers particular advantage. Because most of the mass of an anatomic implant is centered in the lower part of the device, when the implant is placed upright, the magnitude of the distorting forces across the peripheral upper edge of the implant is minimized. As a result, anatomically shaped implants are inherently less likely to wrinkle or otherwise develop a shape distortion than ‘round’ devices, a fact that can afford the surgeon a greater ability to control the shape of the upper pole of the breast (Figure 3.17 A–F). This tendency to maintain shape when placed upright is further enhanced when the fill material has enough structural integrity to support the implant shell. Both saline and standard viscosity gel do not tend to provide strong enough support to the upper pole of an anatomically shaped implant shell and wrinkles and folds can form when these devices are placed under a lax skin envelope. As such, these types of devices are subject to potential fold flaw failure with rupture over time. However, with the newer cohesive gels, which have an enhanced level of viscosity, strong structural support is provided to the entire implant shell and these devices do maintain their shape well, even when placed upright under a lax skin envelope (Figure 3.18 A,B). To support the outer shell further, anatomically shaped cohesive gel devices are filled to a level which much more closely approximates the optimal fill volume determined by the anatomically shaped mandril which made the device. As a result, these types of anatomically shaped cohesive gel devices are very resistant to wrinkle or fold formation and therefore are associated with very low rupture rates (Figure 3.19 A–C).

Figure 3.16 (A, B) Appearance of a spontaneously ruptured semi-cohesive, textured, anatomically shaped silicone gel implant after explantation. A mild capsular contracture created sharp folds in the implant, which resulted in a stress-related crack in the shell with eventual failure of the device.

Figure 3.17 (A, B) Front and side upright views of a textured, anatomically shaped, cohesive silicone gel implant. As a result of both the anatomically shaped shell as well as the firm support provided by the stiffer cohesive gel, the magnitude of the distorting forces that are present about the upper pole of the device are minimized and the implant maintains an anatomic shape without wrinkling even in the upright position. (C) Side view of an upright cohesive anatomic implant as compared to an upright round silicone gel device, demonstrating the marked degree of upper pole collapse that occurs in the round as compared to the anatomic implant. (D) Similar observations can made comparing the anatomic device to an upright saline implant. (E, F) Schematic demonstration illustrating the positive effect that the use of a cohesive anatomic implant is postulated to have on the contour of the upper pole of the breast. Because the anatomic implant maintains its shape in the upright position, better control of the upper pole contour of the breast can be afforded with the shaped device.

Figure 3.18 (A, B) Cutaway view of an anatomically shaped cohesive gel implant, demonstrating the enhanced support the gel provides for the implant shell, even in the upright position.

Figure 3.19 (A, B) AP and lateral views of a patient after undergoing breast augmentation with a 280cc cohesive, textured, anatomic silicone gel implant placed in the subglandular plane. (C) The upright MRI demonstrates that the implant maintains the anatomic configuration in the upright position without the formation of any wrinkles or folds in the shell of the device.

Figure 3.20 represents a graphical summary of these concepts. The quality of the aesthetic result is represented on the Y axis and the percentage of filling of the implant relative to the optimal fill volume is represented on the X axis. The left side of the graph demonstrates that the result provided by a relatively underfilled round gel implant with a less cohesive gel consistency which falls to the bottom of the pocket and assumes an anatomic shape is generally very aesthetic. Thinking about it another way, it is the breast that shapes the implant, which is a very versatile and powerful way to use a device. At the other end of the graph is the result provided by a completely filled, anatomically shaped cohesive gel implant, which can also provide a very aesthetic result. In this instance, it is most decidedly the implant which is shaping the breast, which is also an excellent strategy for using a breast implant. It must be noted, however, that when using the anatomically shaped, cohesive gel devices, a premium is placed on accurately matching an implant of the proper dimensions to the basic measurements obtained from the patient. Because the implant does not conform at all to pressure from the overlying skin envelope, it must be matched well to the existing soft tissue framework to provide the best result. For this reason, anatomically shaped cohesive gel devices are generally less forgiving with regard to sizing errors than their smooth round gel counterparts.

Figure 3.20 Schematic diagram illustrating the two main strategies that can be effectively used in aesthetic breast surgery. The left side of the diagram represents the use of an underfilled silicone gel implant that folds and wrinkles under the breast as dictated by the nature of the overlying soft tissue cover. In essence, it is the breast that shapes the implant. This is a very versatile and effective way to use a breast implant. Conversely, the right side of the diagram represents the use of a fully filled silicone gel or saline implant. Here it is the implant that is shaping the breast. When this is done using an anatomically shaped cohesive gel device, very consistent and aesthetic results can be obtained.

Special note must be made regarding the center portion of the graph. Here, the aesthetic quality of the result has been denoted as being less favorable as compared with the results obtained using the devices noted on either end. The reason for this is related to both the fluid characteristics of the filling material and the shape of the implant shell. As noted earlier, underfilled round implants will form wrinkles when placed upright under the breast. When the implant is a silicone gel device made with a gel that has a soft consistency, the wrinkles tend to fold smoothly and are much less likely to create a visible surface irregularity. Therefore, although the potential for fold flaw failure in these devices is present, experience has shown that these implants can last for decades without rupturing. However, with saline implants, the wrinkles that form tend to be more sharply demarcated and create a sharper edge in the implant shell. The same is true for any type of round or anatomically shaped cohesive gel device that is underfilled. If the stiffness of the gel is not sufficient to support the shell, very sharply demarcated folds will form particularly across the upper pole. Not only does this pose a risk for potentially creating a visible contour deformity in the breast, but the folded shell edge will weaken over time, ultimately leading to implant rupture. One strategy that can be utilized to combat this tendency for a saline implant to wrinkle in the upper pole is to overfill it slightly to help ensure that the volume of the upper pole will be maintained when the device is placed upright (Figure 3.21 A–C). Caution must be used in these circumstances, however, as, while this strategy may help reduce the tendency for the implant to demonstrate upper pole wrinkling, it also tends to create a rounded appearance that might become objectionable in thinner patients.

Figure 3.21 (A, B) AP and lateral views of a patient after undergoing breast augmentation with a 310 cc high-profile, smooth, round saline implant filled to 350 cc in the subglandular plane. (C) The upright MRI demonstrates that the modestly overfilled implant remains fully inflated in the upright position with no wrinkling being evident in the implant shell. Despite the use of a high-profile saline implant in the subglandular plane, a complementary interaction between the implant and the soft tissues has resulted in an aesthetic breast contour.

It was not long after the introduction of the very first generation of silicone gel implants that an anatomically shaped version became available. Intuitively it made sense, even in those early days of implant experience, that if the device was anatomically shaped, a more aesthetic result could be created using such a device. The problem of rotation was recognized early on and one of the first anatomically shaped devices available for general use was manufactured with a series of dacron patches attached to the back. These patches incited a tenacious tissue ingrowth response which locked the device into position and prevented rotation. Unfortunately, these implants were also associated with a capsular contracture rate which approached 100%. The dacron patch was thought to be at least partially responsible for this unacceptably high capsular contracture rate and this device fell from favor (Figure 3.22 A–D). During this time period from the late 1960s and into the 1970s, other design modifications were investigated including the development of saline devices, double-chambered devices and various types of gel implants, most with a ‘round’ shape, and the concept of an anatomically shaped implant became a distant concern. Ultimately, an implant coated with a thin layer of polyurethane foam was developed in an attempt to alter the surface interaction of the device with the surrounding capsule (Figure 3.23 A–C). The resulting capsular contracture rate associated with these devices was very low and ultimately several different designs became available including a round version known as the Meme implant and an anatomic version known as the Replicon (Figure 3.23 D,E). Since that time, several other manufacturers have developed similar devices. This was a critical moment in implant design as it represented one of the first attempts to merge the concept of a using a shaped device with a textured surface that promoted capsular ingrowth. By using this strategy, the shaped device becomes locked into position such that it cannot rotate postoperatively, a critical factor in effectively using a shaped implant. The early shaped polyurethane-coated devices were only mildly anatomic and still maintained a fair amount of upper pole fullness. As a result, early efforts to improve the anatomic shape provided by the devices included a technique of implant ‘stacking’. This involved using a round polyurethane-coated base implant and then positioning, or ‘stacking’, a smaller round polyurethane-coated device on the lower pole of the base implant in an attempt to increase the overall lower pole projection of the breast. The friction provided by the polyurethane coating, along with the tissue ingrowth which occurred along the surface of the devices, tended to maintain the position of the two implants on top of one another to create an overall anatomic appearance.

Figure 3.22 (A, B, C) AP, lateral and posterior views of one of the early shaped silicone gel implants manufactured with five separate dacron patches on the back. These patches were designed to help hold the anatomic device in the proper orientation. (D) Appearance of the capsule after complete capsulectomy. Note the mirror image dacron patch imprints made in the capsule. These patches functioned solidly to bond the patch to the posterior capsule.

Figure 3.23 (A) A polyurethane foam-covered implant. Here the thin layer of foam has been partially freed from the surface of the device to reveal the underlying implant. (B, C) Scanning electron micrograph of the foam structure reveals an open lattice network that allows ingrowth of the capsule into the foam. (D) The Meme implant manufactured by Surgitek combined the polyurethane foam covering with a round silicone gel implant. (E) The Replicon implant, also manufactured by Surgitek, combined an anatomically shaped gel implant with the polyurethane foam covering. (F) Appearance of a Meme implant that has been removed along with the investing capsule. (G) After cutting the capsule free, the dimensions of the implant are restored. The foam has been completely broken down over time, leaving behind the silicone gel implant.

The mechanism of action for the reduced rate of capsular contracture associated with the use of polyurethane-coated implants was eagerly investigated. It had been demonstrated previously that the polyurethane foam lattice network of the polyurethane foam-coated implant underwent gradual degradation over time and that, histologically, multinucleated giant cells could be identified in microscopic sections of capsules from patients augmented or reconstructed with polyurethane foam-coated devices. Small defects could be seen in the foam structure indicative of this gradual degradation. Eventually, over a span of up to 20 years, it has been demonstrated that the foam covering is completely digested away, converting the device into a smooth-walled silicone gel implant (see Figure 3.23 F,G). Coincident with this complete removal of the foam covering has been the development of a contracture in some patients. As a result, it is generally accepted that this mild chronic inflammatory response was either responsible for, or indicative of, a process which prevented the capsule from contracting. Once this foam lattice network was completely removed, the device became simply a smooth round gel implant with an associated rate of capsular contracture indicative of any smooth round gel device. As a by-product of investigation into this process of gradual foam degradation, claims were made that certain breakdown products of the metabolism of the foam were carcinogenic. Although later shown to be of no significant consequence, the results of these claims led to the discontinuation of polyurethane foam-coated implants from production, at least in the USA. Also, the design and use of anatomically shaped implants was sharply curtailed due to the loss of the ability to ensure the devices would maintain their proper orientation.

With the loss of polyurethane foam as an interface between the shell of the implant and the surrounding capsule, efforts were made to replicate in other ways the polyurethane effect. As a result, several different types of surface texturing of standard silicone breast implant shells were developed, each attempting to break up the linear deposition of collagen in the capsule that eventually forms around the implant. Essentially, two different types of surface textures have persisted and are commonly used today in both implants and expanders.

Biocell

This surface texture is manufactured by layering salt granules into a tacky implant shell and then washing them out once the shell has completely cured. The result is an open pore lattice network that creates a roughened surface to the device (Figure 3.24 A–C). Because this is the most aggressive of the textures, actual ingrowth of the capsule can occasionally be demonstrated, particularly when used with tissue expanders, which creates an interesting Velcro-like effect once the device is removed and the capsule is forcibly separated away from the textured surface (Figure 3.24 D). Although the effect of textured surfaces on the rate of capsular contracture remains controversial, there is no doubt that, when textured ingrowth of the capsule occurs, the device is locked into position and cannot rotate. This finding greatly facilitated the subsequent development of a new generation of anatomically shaped tissue expanders and implants and was perhaps one of the most important advances in implant technology in the modern era. Unfortunately, ingrowth of the capsule into the Biocell textured surface is an unpredictable occurrence. Certainly with the anatomically shaped tissue expanders used today, as the device is expanded, the shell of the expander is forced into the capsule as the pressure in the expander increases with each inflation. As a result, it is very common to be able to demonstrate textured ingrowth into the surface of the device when the expander is removed and replaced with the permanent implant. Even here, however, ingrowth is very often incomplete and portions of the surface of the expander do not demonstrate any ingrowth. But there is usually enough to stabilize the anatomic expander in position and nearly every tissue expander manufactured today has some type of textured surface to help stabilize expander position and orientation. With anatomically shaped implants, however, the compressive forces around the implant are invariably less vigorous and there is less impetus for the capsule to grow into the Biocell textured surface. As a result, textured ingrowth is found much less commonly in both round and anatomically shaped implants.

Figure 3.24 (A) Gross appearance of the Biocell textured surface. (B, C) Scanning electron microscope (SEM) appearance of the Biocell surface, revealing the open pore lattice network. (D) Adherence of a portion of the capsule to the textured surface.

One interesting observation noted with Biocell textured devices is the occasional formation of a ‘double capsule’ around the implant. Inside the capsule that forms in association with the surrounding soft tissue of the pocket is a second pseudocapsule that becomes densely adherent to the textured surface of the device (Figure 3.25 A). This inner capsule has a smooth outer surface and demonstrates solid ingrowth into the textured surface that must be peeled away from the implant to be effectively removed. Histologically, this tissue is characterized by a multi­laminate scaffold of collagen within which is interspersed a sparse population of fibroblasts (Figure 3.25 B). This is an extremely interesting finding given that the inner capsule is a separate tissue layer that maintains no direct link to the surrounding capsule and therefore has no apparent source of vascular supply. It can be postulated that these cells have a very low metabolic requirement and are surviving on diffusional sources of oxygen and energy alone. One possible etiology for the formation of the inner capsule may be related to seroma formation in the pocket around the implant, although exactly how the fibroblasts are able to populate the surface of the device and then proliferate enough to form a distinct fibrous layer remains unknown. In most instances, the development of an inner capsule is a benign occurrence that only partially involves the surface of the implant and, as such, simply represents an area where the outer capsule cannot grow into the textured surface of the device (Figure 3.25 C). Occasionally, however, the implant becomes completely surrounded by the fibrous layer of the inner capsule and since the interspace between the two very smooth capsules is mildly lubricated, the implant can rotate and flip in the pocket with ease. As a result, when double capsule formation occurs in association with a shaped implant, the risk of undesirable implant rotation becomes greater (Figure 3.25 D,E).

Figure 3.25 (A) Appearance of the inner pseudocapsule attached to the Biocell textured implant. (B) Histologic appearance of the inner capsule reveals a sparse population of fibroblasts in association with a multilaminate layered collagen matrix. Small reractile bodies are present in the surface and represent small pieces of silicone rubber from the textured surface that were broken off when the capsule was peeled away from the implant. (C) Appearance of the posterior surface of a Biocell textured implant, demonstrating partial coverage of the posterior portion of the device with an inner pseudocapsule. (D) Appearance of a Biocell textured anatomically shaped cohesive gel implant along with the capsule that surrounded it. The implant is completely coated with an inner pseudocapsule. (E) Appearance of the implant after the pseudocapsule is peeled away from the implant.

Siltex

This surface texture is manufactured by pressing a layer of polyurethane foam into a thin tacky sheet of silicone rubber which has been affixed to the shell of an otherwise smooth implant. In this fashion, an imprint of the irregular polyurethane foam surface is reproduced on the surface of the textured device. This design was meant to duplicate the pore size of the interstices of the native polyurethane foam and thus, theoretically, duplicate the positive effect polyurethane has on reducing the rate of capsular contracture. The net effect of this technique is a less aggressive texture which does not promote tissue ingrowth (Figure 3.26 A–C). The effect of this texture, and also, the Biocell texture when ingrowth does not occur, is to provide a rough surface that tends to stabilize the implant and inhibit sliding of the implant across the smooth surface of the capsule. It is analogous to the effect the ridges present in fingertips have on grasping ability. By creating a rough surface on the device, sufficient friction is created to inhibit implant rotation and, along with other factors such as pocket dimensions, help keep an anatomically shaped tissue expander or implant properly oriented.

Figure 3.26 (A) Gross appearance of the Siltex textured surface.(B, C) SEM appearance of the Siltex textured surface.

At first glance, breast implants appear to be simple devices. However, designing, manufacturing, using and understanding breast implants can be a surprisingly difficult task. For patients who have a thick soft tissue layer over the chest wall, these decisions are not so hard and basically any type of implant will provide variably excellent results. Where the difficulty arises is in just those patients who tend to present for breast augmentation, namely women who have a small breast, who are thin and who do not have an adequate soft tissue layer to mask the deficiencies associated with a poorly chosen implant. Here, all these variables come together and a premium is placed on proper implant selection to provide the best result possible.

From my perspective, after having used all of the devices discussed in this chapter, there are several general conclusions I believe to be valid and these conclusions continue to guide my implant selection process today:

In this chapter, I have attempted to outline the various physical factors that govern how an implant will perform once it is filled to a certain volume and then placed under the soft tissue framework of the breast. Understanding and applying these concepts to maximum advantage is vital in order to obtain the best results possible in aesthetic breast surgery.