This chapter focuses on comparing and analyzing randomized controlled studies to allow evidence-based knowledge about breast implants. In the field of plastic surgery, designing these studies is much more challenging than in other medical fields. Here, we analyze recent randomized controlled studies (RCT) in the field of aesthetic augmentation with breast implants tempting to provide a high-level evidence-based chapter. Despite the central role of aesthetic breast reconstruction, the best implants to use have rarely been studied in the context of large sample size RCTs. Though some RCTs have been performed representing the best evidence currently available34, they are often underpowered being inconsistent in their findings making conclusions difficult.
Breast augmentation is one of the most commonly performed aesthetic procedures with breast implants being a mainstay of modern medicine. The key to success of the perfect implant placement is careful preoperative patient selection, incision location, implant type and keeping the implant in the accurate position. Choosing implant shape and texture is one of the most essential yet controversial decisions in aesthetic breast augmentation.
Additionally, this chapter covers postoperative treatment methods, complications and surgical side infection as well as recommendations for the use of antibiotics (Figure 1). After aesthetic breast augmentation, up to 2.9% of women develop infection5.
For the first time, we will depict several RCTs about aesthetic breast augmentation with implants while our experts will debate about the outcome and practicability of these trials. This chapter will meta-analyze previous clinical trials to investigate the role of breast implants in augmentation patients and will provide optimized surgical procedures.

Breast augmentation is one of the most commonly performed aesthetic procedures with breast implants being a mainstay of modern medicine. 
There is ample evidence that inadequate breast appearance can adversely affect self-esteem and body image, and this can be improved with augmentation mammoplasty6. First of all, for aesthetic reasons, there is implant-based breast augmentation. Implants are classified in different types depending on shape, surface and consistence. Many surgeons choose implants based on personal experience or expert opinion. Cheng et al. and Hidalgo et al. independently performed meta-analyses and RCTs stating no aesthetic superiority of anatomical implants compared to round implants78. 
Regarding the surgical procedure, classifications depend on incisional technique, implant pocket placement and inframammary fold positioning. A Level of Evidence II study showed atrophy of the breast parenchyma after subglandular breast augmentation, but not following submuscular breast augmentation. In contrast, submuscular breast augmentation caused atrophy of the pectoralis major muscle9. Capsular fibrosis (CF) is the main long-term complication of breast implants. Combined data from previous RCTs suggest that the use of textured implants decreases the risk of this foreign body complications but (macro-)textured implants might be associated to an increased risk of breast implant–associated anaplastic large cell lymphoma (BIA-ALCL)1011. 
Recent retrospective long-term studies have demonstrated negligible difference between textured and smooth implants with regard to the occurrence of CF13. Randomized controlled trials are required for a definitive understanding of the efficacy of surface texturing as there are no existing randomized controlled trials of modern smooth vs textured implants in the last 20 years.After aesthetic breast augmentation, up to 2.9% of women develop infection, with an incidence rate of 1.7% for acute infections and 0.8% for late infections5. Guidelines by the Centers for Disease Control (CDC) recommend surgical wounds be covered with a sterile dressing for 24 to 48 hours. An RCT performed in 2018 emphasized application of postoperative dressings play a key role in risk reduction. 
In primary augmentation, a single dose of intravenous weight-based cefazolin given 60 min before skin incision appears to be adequate. Clindamycin or vancomycin are recommended for patients with β-lactam allergies. In secondary breast surgery, fluoroquinolones and vancomycin should be given 120 min before first incision (Figure 1). Using these principles of the 14-point plan by Adams et al. to minimize the bacterial load at the time of surgery, the development of subclinical infection and capsular fibrosis may be reduced significantly. No one approach suits every patient, and surgeons must be versed in many techniques to best serve individual variations in anatomy, surgeon and patient goals. The simple choice of implant size has been replaced with the objective measurement and planning of a detailed and patient-specific operation.

Breast augmentation (=augmentation mammoplasty) uses breast implants or fat transfer to increase the size, change the shape/volume, and alter the texture of females´ breasts. 

Most commercially available breast implants feature some degree of elastomer surface modifications to increase surface roughness. However, manufacturing processes of breast implants differ from company to company, including a differently used taxonomy, complicating valid scientific comparisons between breast implants of different companies.

Silicone gel implants vary in terms of gel cohesivity and form stability. Various degrees of gel cohesivity are obtained by varying the density of crosslinking between silicone polymers17. Less cohesive gels are less crosslinked, are more elastic, and have a softer feel while more cohesive gels more crosslinked, are less elastic, and have a firmer feel. Silicone gel filled implants have been improved since their introduction and nowadays fourth and fifth-generation gel devices are available1819.

One result of anatomically shaped breast implants combined with a more cohesive gel is that collapse and wrinkle formation of breast implants can be prevented.

Implant “profile” is not the same as implant projection. Implant projection is a quantifiable linear measurement of the anterior–posterior dimension of the implant, whereas implant “profile” is a vendor-driven assessment that currently lacks universal standardization. Until “profile” assessments are standardized across vendors, it behooves us to be cognizant of their limitations as primary variables used to guide implant selection.
The confusion between implant “profile” and projection arises from the occasional misuse of the 2 terms interchangeably. Commonly, implant “profile” is inadvertently referred to as its “projection” (i.e., calling a “high profile” implant a “high projection” implant). Implant projection is the linear measurement of the anterior–posterior dimension of an implant. It is a single, numerical dimension, whereas “profile” is a 3-dimensional descriptor of implant projection (and hence, volume) relative to its base diameter. In essence, “profile” encompasses a permutation of all 3 implant dimensions, whereas projection represents only a single dimension20.
Nowadays, we have an inconsistent use of “profile“ classifications, where multiple manufacturers have independent control over their implant classifications, what holds true for a high-profile implant from a certain vendor may not hold true for a similarly classified implant from another. Adding to the confusion is the variety of descriptors that have been added to the traditional profile types, such as low-plus, moderate-classic, moderate-plus, moderate-high, midrange, full, extra-full, and ultra-high profiles (Figure 3).

Surface texture of a breast implant influences tissue response and ultimately device performance. Smooth implants can move around within the capsule, but this does not cause a change in appearance the way textured implants do when they move. Texturing is considered a requirement to provide friction and reduce malposition. To mitigate the risk of capsular fibrosis (CF), the implant´s shells were textured based on the theory that an irregular shell surface would prevent the parallel alignment of collagen fibers thus, by extension, preventing CF21.  Preliminary studies supported this theory with an observed reduction in CF rates23 but recent implant studies have demonstrated negligible differences in contracture rates between textured and smooth styles1213.
Recent research has suggested a reproducible association between textured implants and the development of breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), a potentially fatal T-cell lymphoma (see section Complications: BIA-ALCL).
Conclusively, Polyurethane-coated implants (PU) have the highest surface area and were an attempt to reduce capsular fibrosis but were prone to degrade. Thus, resulting in a thin, pliable shell that was more susceptible to visible folds, rupture, silicone leakage and late presumably CF2425. 

Is there an ideal breast?
Beauty is in the eye of the beholder-this proverb is as old as it is true. 
The authors of this chapter can´t agree more, especially when it comes to the perfect aesthetic breast. 
There rarely have been objective data in the plastic surgical literature to define an aesthetically pleasing template for the ideal breast that everybody agrees upon.
Mallucci et al. propose that the perfect breast with universal appeal has an upper pole-to lower pole ratio of 45:55 (slightly fuller lower pole than upper pole), an upward pointing nipple (20-degree mean angle), a straight/mildly concave upper pole slope and a smooth lower pole convexity26 (Figure 5). The breasts’ overall aesthetic appeal is more important than their size.

Here, we try to identify some key parameters as the basis for the design of ideal breast proportions by combining recent studies that have tried to identify some key parameters that nearly everyone agrees upon and show our own best practice. The most important consideration when it comes to breast augmentation is the patient´s own personal goals for the procedure.

In the High Five System analysis28, variables are analyzed including implant volume, patient’s base width, implant base width, anterior pulled skin stretch, and nipple-to-fold distance under maximal stretch. Based on the selected implant, a reference chart provides the desired nipple-to-fold distance, which if longer than the measured distance, will require IMF lowering (Figure 7).

Based on our experience, we think that the best way to identify the new IMF is with patient’s arms lowered and secondly elevated (see above "IMF and Implant Volume"). But there are many different ways to identify the new IMF.

Dr. Bradley Calobrace for example recommends the following: “The true fold, the best predictor of where the fold will lie postoperatively, is assessed by autorotation of the breast inferiorly to identify the inferior extent of the fascial attachments at the fold.”29.

As always, there is no single unique and absolutely correct technique but each system contributes significant critical detail to the breast surgeon’s ability to provide reproducibly, beautiful and safe results.

The selection of the implant height should follow the patient’s breast implantation base, which is highly influenced by the body type. With this assumption, the “number Y” was developed30. It correlates the suprasternal notch-to-nipple distance with the thoracic perimeter and reveals the shape of the optimum breast implant base in the particular patient. The number Y can help to rationalize the selection of the implant height in breast augmentation.

Calculation according an average body-size woman with thorax circumference of about 75cm (Modified from Botti G et al.):

 If change of breast pocket is performed: see First Aesthetic Implantation of Breast Implants

Scandals concerning breast implants confuse patients, medical doctors and the public. Until now legally binding consequences are missing despite repeated requests. Since 2013 we have developed and implemented an own breast implant template for the daily clinic routine in Regensburg to increase the patient's safety and the assessment of implants in course of time31. The breast implant template optimizes the quality of surgical treatment and outcomes, quickly reveals complications, allows valuable tracing of breast implants and improves the consultation of patients.

Bottoming out and double-bubble represent common iatrogenic deformities for revision surgery in breast augmentation with breast implants. 
Both are a malposition of the implant. While bottoming out is an inferior implant displacement with a high riding nipple, resulting in the lower pole being longer than it should be, double bubble is clinically characterized by double convexity of the lower pole due to the visible indentation of the old inframammary fold (IMF) that sits in the middle of the two convexities. Several clinical studies have been done to face this complication.

Implant is below breast mound:

Salgarello et al. performed an anatomical and clinical study of women who underwent breast augmentation. They state that deformities can be avoided if an anatomical approach is used during pocket dissection at the level of the IMF, paying attention to avoid disrupting the superficial and deep attachments of the superficial pectoralis fascia at the IMF32.

Capsular fibrosis around breast implants is the most common long-term complication. This complex foreign body response will be discussed in detail in Chapter: Implant Diagnostic.

Symmastia is the migration of one or both implants across the midline, leaving (almost) no natural sinus. Symmastia can be the result of: 

Recent research has suggested a reproducible association between textured implants and the development of breast implant–associated anaplastic large cell lymphoma (BIA-ALCL), a possibly fatal T-cell lymphoma. Although rare, the presence of a textured breast implant is thought to increase the risk of developing breast ALCL by an estimated 67 to 421 times33. Late-onset seroma and periprosthetic effusion are a rather common presentation, and few patients present with a firm mass. Thus, any delayed seroma occurring more than one year after implantation not explainable by infection or trauma might potentially be associated with BIA-ALCL and should therefore be investigated through fine-needle aspiration, flow cytometry, and CD30/ALK immunohistochemistry3435. 
Concerns for causing malignancy in elective surgical patients have led the plastic surgery community to prioritize BIA-ALCL investigation, with numerous recent publications on the topic and the creation of a national registries in different countries313637383940. Since the first reported case in 199741, the incidence of patients with BIA-ALCL has been rapidly increasing, possibly due to an increased awareness. The U.S. Food and Drug Administration has been tracking and investigating ALCL and has released a report linking ALCL to textured implants42.
NCCN guidelines on BIA-ALCL have been recognized by the US Food and Drug Administration. Consensus guidelines have helped create a treatment standardization for BIA-ALCL at all stages of disease. NCCN guidelines are evidence-based where possible and utilize expert consensus opinion to fill in gaps that may exist. Recommendations focus on parameters for achieving reliable diagnosis and disease management and emphasize the critical role for complete surgical ablation. Suggestions for adjunct treatments and chemotherapy regimens are included for advanced BIA-ALCL with lymph node involvement.
Plastic surgeons must weigh many variables and consider all risks and benefits when selecting implants for each individual patient.

Since the introduction of the breast implants in 1962, breast augmentation has become one of the most frequently performed operations in plastic surgery. As we strive for perfect results, it is important to continue to gather and review data evaluating innovative techniques and devices43. Now we even have more options available for breast augmentation, whether we use them in combination or alone. By combining all of the available options (acellular dermal matrix products, silicone implant, fat grafting), "bioengineered breasts" can be created with high patient and surgeon satisfaction.
Biodegradable breast implants could be a novel and future approach for breast reconstruction using 3D-printed implants. Several companies are currently developing porous, biocompatible and absorbable breast scaffolds where absorbable polymer technology is used and after implantation, aims to enable regeneration of natural breast tissue. The scaffold aims to guide the growth of natural tissue with the use of patient's own body fat harvested via routinely practiced liposuction procedure and injected into the customized 3D-printed implant. Over time, this implant absorbs leaving solely the injected fat tissue in a naturally shaped breast form.

This video contains useful information how to perform individual preoperative planning and essential markings on a patient  (breast augmentation with breast implants).

This sheet will be useful for every surgeon to quickly check the most important landmarks when it comes to optimized breast implant selection. Use it as a sheet that easily fits in your doctor´s coat´s pocket (Figure 14).