Risk Of Leakage In Newer Cohesive Gel Silicone Breast Implants?

Silicone Gel-filled Breast Implant Failure Rate

A detailed answer to your questions deals with several factors including shell failure, capsular integrity, and silicone chemistry. I apologize a head of time if this bores you.

A very rough estimate of implant failure is about 1% per year. This estimate holds true for the earlier years, but since breast implants are not considered permanent medical devices, the failure rate does increase as the implant ages.

In June 2011 the FDA published a report entitled, FDA Update on the Safety of Silicone Gel-Filled Breast Implants, which served to provide an update of the clinical information about the silicone gel breast implants approved in November 2006.

As a condition of approval, the FDA required the implant manufactures to conduct several post-approval studies, including: (1) the Core Study, (2) the Large Study, (3) and a Device Failure Study. These studies also evaluated breast revision and reconstruction patients, but I have not included that material here.

The Core Study followed women with silicone gel-filled breast implants enrolled in “pre-approval” studies (conducted before the approval of gel implants), which involved follow-up clinical assessments of patients at 6 months, 1 year, and then annually for a total of 10 years. Participants were assigned to either an MRI group or a non-MRI group. Participants in the MRI group received MRIs on a specific schedule to screen for rupture, but the timing of the MRI assessments and the methods of assigning participants differed between the manufacturers. The cumulative incidence of rupture rates among Allergan implants in the MRI group 10 years after primary augmentation was 10.1% (7.4% - 13.7% at 95% confidence intervals). The cumulative incidence of rupture rates among Mentor implants at 8 years after primary augmentation was 13.6 % (7.6% - 23.6% at 95% confidence intervals).

The Large Study was started shortly after the FDA approved the use of silicone gel-filled breast implants in November 2006. The Large Study was designed to be large enough to address issues that the Core Studies could not answer, and to provide a real-world assessment of some outcomes of silicone gel-filled breast augmentation. The purpose of the Large Study is to determine the incidence of complications and other adverse outcomes - including local complications, rupture, connective tissue disease, cancer, effects on mammography, in addition to several others.

Allergan’s Large Study enrolled 41,342 women with silicone gel-filled breast implants, and a control group of 15,646 women with saline-filled breast implants. Allergan initiated patient enrollment in February 2007 and closed enrollment in March 2010. Two years after implantation, the participant follow-up rate was 60.5% for silicone gel-filled breast implant participants and 45.1% for saline breast implant participants. The latest published results are from 2010. The 2-year cumulative incidence of implant failure is 0.5% for silicone gel-filled breast implants and 2.5% for saline breast implants. Data collection is ongoing.

Mentor’s Large Study enrolled 41,975 women with silicone gel-filled breast implants and a control group of 1,030 women with saline-filled breast implants. Mentor initiated patient enrollment in February 2007, and closed enrollment in July 2009. Three years after implantation, the participant follow-up rate was 21.1% for silicone gel-filled breast implant participants and 9.6% for saline breast implant participants. The latest results are from 2010 and include data for all participants with 3 years of follow-up. The 3-year cumulative incidence of implant failure is 0.2% for primary augmentation patients. Data collection is ongoing. The results of both Large Studies are somewhat limited by a low follow-up rate. The FDA and manufacturers are working to encourage patients to continue their participation in these studies.

The purpose of the Device Failure Study is to evaluate silicone gel-filled breast implants that have been removed (for what ever reason) and returned to the manufacturers; the manufacturers are to document and record the mode of failure in hopes of improving implant design and surgical techniques for placement. Each manufacturer is required to conduct studies of all returned devices until both the Core Study and the Large Study are completed. Again, the data collection and analysis varies by manufacturer.

Allergan has evaluated 2,665 returned devices: 900 (33.8 %) had openings in the shell. Of the devices with an opening in the shell: 51 (1.9 %) devices had fold flaws; 26 devices (1 %) had manufacturing defects; 487 (18.3 %) had some sort of surgical-related damage; and 336 (12.6 %) had openings for which the cause could not be determined.

Mentor recorded their data differently. Among patients participating in the Mentor Large Study, 62 silicone gel-filled breast implants have been evaluated: 27 devices (43.5 %) had openings in the shell. Of the devices with an opening in the shell: 12 (19.4%) were damaged by sharp instruments; and 15 (24.2%) had openings of unknown cause. Among Core Study participants, 97 devices were returned to Mentor: 24 devices (24.7%) had openings in the shell. Of the devices with an opening in the shell: 8 (8.2%) were damaged by sharp instruments; 2 (2.1%) had partial delamination in the shell or patch junction; and 14 (14.4%) had openings of unknown cause.

These studies all deal with moderately cohesive silicone gel-filled breast implants, identical to the ones used today. Understanding and comparing failure rates is difficult because the two manufacturers conduct their studies differently, so it is often not an apples-to-apples comparison when reviewing the data. But this should give you some idea as to the incidence of failure, and its causes.

Silicones are polymerized chains that include the elements silicon (Si) and oxygen (O) in a repeating backbone, together with carbon and hydrogen. Because of the repeating (… -Si-O-Si-O-Si-O-Si-O- …) units, silicones are referred to more scientifically as polymerized siloxanes or polysiloxanes. The simplest and most common silicone/polysiloxane is linear polydimethylsiloxane (PDMS). Common forms of silicone (of different consistencies) include silicone oil, silicone grease, silicone rubber, and silicone resin.

Liquid silicones are comprised of short chains of PDMS with very little cross-linking between chains; they have the consistency of an oily fluid.  Silicone gels are composed of longer PDMS chains and some degree of cross-linking between chains. The viscosity and cohesiveness of a silicone gel increases as the PDMS chain length and degree of cross-linking increases.  The consistency of silicone gels vary widely from a soft, sticky gel with more fluid-like properties to a firm, cohesive gel exhibiting shape retention or form-stability.  Today, the silicone gel used to fill breast implants has a rather consistent polymer length with a rough average of 335 dimethylsiloxane units. The silicone gel filler in 2nd generation implants (prevalent in the 1980s) was comprised of some slightly shorter polymer chains, with less cross-linking between chains; this accounted for the thinner lower cohesive nature of this gel filler. As the silicone gel fillers have increased in viscosity and cohesiveness the degree of cross-linking has increased; the primary difference between a “moderately cohesive” 4th generation gel (currently approved) and a “form-stable” 5th generation gel (investigational, gummi bear) is the increased amount of cross-linking between the silicone polymer chains.

No one can give a specific answer about what exactly happens to the silicone gel when an implant shell fails. The rate and amount of gel exiting the lumen of the implant depends upon the mechanism of failure, the size of the hole in the implant shell, and the age of the failure. The gel matrix of the current (4th generation) silicone gel-filled implants is certainly more cohesive than that of the 2nd generation gel-filled implants used in the 1980s. Although the flow characteristics of these gels are difficult to describe, those older implants certainly had more of an ‘oozy’ consistency. I recognize that the word ‘ooze’ is perhaps not the best description, but it does help convey the consistency of this gel. History has shown that these 2nd generation implants have the highest failure rate of any silicone gel-filled device. When these implants have failed, at the time of surgical removal, there is often a significant amount of gel that has leaked outside the shell. It is easy to see that in a situation where capsular integrity is lost, this less cohesive gel will more easily travel (ooze) to an extracapsular location. The gel inside a current 4th generation implant has some structure due to the moderately cohesive nature this matrix; it is thicker, has a tendency to stick together and partially maintain its shape. In other words it has less of that ‘oozing’ consistency.

The inflammation associated with a long-standing silicone gel failure may lead to loss of capsular integrity and allow the gel to leak from the capsule. However, it is important to note that surgeon’s used to treat capsular contracture with a procedure called a closed capsulotomy. This is a rather barbaric technique where the women’s breast is squeezed with a significant amount of pressure to rupture the capsule. Since silicone gel failure can lead to capsular contracture, it is easy to understand that a closed capsulotomy may have been an easy way to inadvertently allow leaking gel to escape outside the capsule and enter surrounding tissues. From there gel could slowly migrate to numerous locations. Closed capsulotomies are no longer recommended.

The question of silicone traveling to other areas is therefore related to the integrity of the capsule surrounding the breast implant. As long as this capsule remains intact, any silicone gel outside the implant will not be able to escape to the surrounding tissues. Some consider the capsule to be rather protective in that manner, and failure of a silicone gel implant is not an emergency. Some physicians have different opinions about the urgency with which a failed silicone gel should be replaced. It is my recommendation that a failed silicone gel implant be replaced, sooner rather than later; and women are usually happy to follow these recommendations.

The current devices and surgical techniques have evolved. These improvements make the ‘horror stories’ you refer to much less likely. I hope this is helpful and puts things in perspective. Best wishes, Kenneth Dembny

Hi and thank you for your question. The concept of cohesiveness relates to the thickness or viscosity of the gel. Silicone is a wonderful substance that promotes hardly any reaction from the human body. It comes in a wide variety of viscosities, ranging from a water like substance to a hard plastic. This is due to the connections, or cross linking between silicone molecules. The more connections between the silicone molecules, the more viscous the silicone is. Implant manufacturers have taken advantage of this property and have created gummier implants. In fact, one of them created the “gummy bear” implant several years ago, claiming it was superior to all other implants. This resonated with the public and patients often request that I place gummy bear implants. The fact is, nearly all implants are cohesive, form stable silicone implants that are better that the fourth generation gummy bear implants. 

The old silicone was more like syrup and when the implant broke it leaked out like an egg yolk, and could be seen on regular mammogram. The new one are more cohesive and when they break they just sit there and when you do pull one of the new ones out, it has a tendency to come out in one big piece rather then strings of silicone. Much better but really only seen on MRI