 They were introduced in the 1970’s.
They are covered with polyurethane foam.
The incidence of capsular contraction is dramatically lower compared to either smooth or textured implants. The literature quotes 8-9 % compared to 1-2 % with a 15 year follow up.
Capsules are thought to be caused by inflammation, possibly by a staphylococcus epidermidis (from the skin or breast ducts), haematoma, radiotherapy (100%), bacteraemia (with infection elsewhere) or it may be multi-factorial.
Non polyurethane implants elicit a relatively short-lived, avascular and acellular inflammatory response. Collagen fibres are deposited in a parallel, linear array. As contraction occurs, the parallel orientation predisposes to linear contracture, resulting in spherical deformity and firmness of the implant.
When polyurethane is implanted it causes an intense foreign body reaction with neo-vascularisation and infiltration of large numbers of histiocytes and foreign body giant cells. Collagen fibres are deposited in a configuration that mirrors the open cell architecture of the foam. This results in a unique sponge like scar tissue capsule.
“This discovery perhaps explains the absence of capsular contraction amongst most polyurethane covered mammary implants”. (Brand. K. Gerard. Plastic Reconstr. Surg. 1984).
This does occasionally cause an allergic skin rash (1-2%). It generally begins within 2 weeks of surgery and is characterised by diffuse erythematous (redness) rash and pruritis (itching) and subsides spontaneously within 2 – 4 weeks. It can be treated with anti-histamines.
Rippling occurs mostly in the superior pole of the breasts and along the inferior edge. This has the same incidence in all implants. Ripples are the result of the combination of tight pouches with insufficient tissue cover. A sub-muscular plane may help prevent this phenomenon. The sub muscular plane is also used as it is thought to decrease the incidence of capsular contraction. A major benefit of polyurethane implants is being able to use the natural result of the sub glandular plane without the fear of increasing the rate of capsular contracture. This does therefore lead to a greater flexibility in the choices that can be made pre-operatively.
All the other local complications are the same as smooth or textured implants
i.e.
- infection (less than 1%)
- haematomas (0.9 – 2.3 %)
- implant rupture (0.3 – 1.4%)
There is less rotation as the porous implant surface sticks to the fibrotic capsule like Velcro. Polyurethane foam used as a coating undergoes gradual chemical degradation. Chemical analysis using gas chromatography has confirmed the presence of small amounts of 2, 4 – toluenediamine in the urine but it has not been detected in serum (blood). It is thought that the quantity released is not carcinogenic in humans (2,4-TDA is a known rodent carcinogen).
The FDA, the North American Food and Drug Administration Agency, said “based on the very small quantities of TDA found in urine, the potential risk of cancer, if any, is probably negligible”. The FDA estimates that the excessive risk of cancer as a result of exposure to TDA is around one in a million in a woman’s lifetime.
There is historical evidence to support the safety of polyurethane foam in medical devices. Polyurethanes have been implanted for decades in pacemaker connectors, haemodialysis tubing, percutaneous shunts, vascular patches and grafts.
In conclusion, the capsular contraction rate after all types of breast surgery is lower with polyurethane foam covered implants. This benefit persists long term, at least ten years after implantation.
“One particular feature is that the implant remains behind the breast and follows it in all its natural movements instead of displacing itself freely throughout the capsular space”. (Vasquez M.D. Pg 334)
“There is nothing in the experimental literature to suggest that polyurethane foam, or its in vivo breakdown products, pose a threat to the health or safety of patients”. (Handel, N M.D. Pg 272)
Sources
- Brand, K.G. Polyurethane coated silicon implants and questions on capsular contraction. Plast. Reconstr. Surg. 1984.)
- Handel, N, M.D. Long term safety and efficiency of polyurethane foam covered breast implants. Aesth. Surg. 2006. 265 – 274)
- Vàsquez, G, M.D. and Pellòn, A, M.D. Polyurethane Coated Silicon Gel Breast Implants used for 18 years. Aesth. Plast. Surg. 31: 330-336, 2007.
- Forum on polyurethane mammary implants. Brazilian Plastic Surgery Society. July 30th & 31st,2007.
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