Acceleration of capsule formation around silicone implants by infection in a guinea pig model.

Fibrous capsules surrounding silicone implants were investigated in a new guinea pig model to delineate some of the factors leading to capsular contracture. Both the implant surfaces and tissue capsules were examined by light and scanning transmission electron microscopy (STEM + SEM) with x-ray energy spectroscopy (XES). The capsular tissues were qualitatively similar to those recovered clinically, showing dense parallel collagen deposits, fibroblasts, myofibroblasts, macrophages, and foreign-body giant cells. Silicone was positively identified within intercellular vacuoles and the rough endoplasmic reticulum of macrophages by XES. Tissue recovered from the capsules that surrounded implants that were contaminated with S. aureus presented a qualitatively similar histologic spectrum. The contaminated specimens did show an accelerated response. SEM showed a cellular invasion of the silicone envelopes. We conclude that the model accurately simulates the clinical situation and suggests that immune mechanisms may play a key role in capsular contracture.